How to apply fungicide?

Fungicides

Fungicides are pesticides that kill or prevent the growth of fungi and their spores. They can be used to control fungi that damage plants, including rusts, mildews and blights. They might also be used to control mold and mildew in other settings. Fungicides work in a variety of ways, but most of them damage fungal cell membranes or interfere with energy production within fungal cells.

Keep these tips in mind when using fungicides:

  • A fungal disease in plants can be misdiagnosed easily. Check with your local county extension office for help identifying plant disease. They may also be able to recommend a treatment strategy for your lawn or garden.
  • Often, plant diseases are transmitted when leaves are wet. Ground level watering and good air circulation can be used to keep leaves dry.
  • Many fungicides remain on the surface of plant tissues and do not spread throughout the plant. Others penetrate the cuticle and circulate through plant tissues.
  • Pruning shears and other tools can carry plant diseases from one plant to another. Learn about garden sanitation to prevent spreading fungal pathogens yourself.
  • Although they can slow or stop the development of new symptoms, many fungicides are designed only to prevent disease. These are not highly effective after symptoms have developed.

Additional Resources:

Last updated August 02, 2019

Fungicide

Fungicide, also called antimycotic, any toxic substance used to kill or inhibit the growth of fungi. Fungicides are generally used to control parasitic fungi that either cause economic damage to crop or ornamental plants or endanger the health of domestic animals or humans. Most agricultural and horticultural fungicides are applied as sprays or dusts. Seed fungicides are applied as a protective covering before germination. Systemic fungicides, or chemotherapeutants, are applied to plants, where they become distributed throughout the tissue and act to eradicate existing disease or to protect against possible disease. In human and veterinary medicine, pharmaceutical fungicides are commonly applied as topical antifungal creams or are given as oral medications.

powdery mildewPowdery mildew on pumpkin leaves.Jeff KubinaRead More on This Topic surface coating: Fungicides, bactericides, and other specialty additives In order to stabilize aqueous latex coatings for long-term storage, bactericides are often added. Similarly, latex coatings for exterior…

Bordeaux mixture, a liquid composed of hydrated lime, copper sulfate, and water, was one of the earliest fungicides. Bordeaux mixture and Burgundy mixture, a similar composition, are still widely used to treat orchard trees. Copper compounds and sulfur have been used on plants separately and as combinations, and some are considered suitable for organic farming. Other organic fungicides include neem oil, horticultural oil, and bicarbonates. Synthetic organic compounds are more commonly used because they give protection and control over many types of fungi and are specialized in application.

Cadmium chloride and cadmium succinate are used to control turfgrass diseases. Mercury(II) chloride, or corrosive sublimate, is sometimes used as a dip to treat bulbs and tubers; it is highly toxic to humans. Strobilurin compounds are used in industrial agriculture to kill various types of mildews, molds, and rusts. Other substances occasionally used to kill fungi include chloropicrin, methyl bromide, and formaldehyde, though the use of these fungicides is regulated or banned in many countries. Many antifungal substances occur naturally in plant tissues. Creosote, obtained from wood tar or coal tar, is used to prevent dry rot in wood.

Fungicides kill pathogenic or parasitic fungi by disrupting their critical cellular processes. For example, many fungicides bind with specific enzymes to interrupt the metabolic pathways involved with cellular respiration. However, as with herbicides, insecticides, and antibiotics, the overuse of fungicides has led to the evolution of resistance in certain fungal species. Fungicide resistance, in which a fungal population displays decreased sensitivity to a given fungicide, can occur rapidly, as a single fungus may produce millions of spores.

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Fungicide: Modes of Action and Possible Impact on Nontarget Microorganisms

Abstract

Fungicides have been used widely in order to control fungal diseases and increase crop production. However, the effects of fungicides on microorganisms other than fungi remain unclear. The modes of action of fungicides were never well classified and presented, making difficult to estimate their possible nontarget effects. In this paper, the action modes and effects of fungicides targeting cell membrane components, protein synthesis, signal transduction, respiration, cell mitosis, and nucleic acid synthesis were classified, and their effects on nontarget microorganisms were reviewed. Modes of action and potential non-target effects on soil microorganisms should be considered in the selection of fungicide in order to protect the biological functions of soil and optimize the benefits derived from fungicide use in agricultural systems.

1. Introduction

Soil is arguably the most important resource for food production. It is a very complex system whose functions not only depend on its physical properties, but also on its biological components. In particular, soil microorganisms are essential players in the cycling of several elements essential to life, including C, N, and P .

Understanding the effect of fungicides on the beneficial activities of microorganisms is important to assess the hazards associated with fungicide used in agriculture. Crop productivity and economic returns will be maximized with the use of products controlling well fungal pathogens, but preserving beneficial organisms. Different organisms may possess identical or similar mechanisms and constituents, and fungicides targeting nonspecific binding sites can directly affect nontarget organisms. For example, the toxicity of carboxylic acid fungicides is derived from the ability of these chemicals to bind on DNA topoisomerase II, as common enzyme that unwind, and wind, DNA to allow protein synthesis and DNA replication. This enzyme is found in fungi but also in prokaryotic cells . Some glucopyranosyl antibiotic fungicides are toxic to bacteria, in which they may inhibit the synthesis of amino acids . These fungicides are also toxic to certain nonfungal higher eukaryotic organisms .

Indirect nontarget effects are also possible. Microorganisms are either functionally or nutritionally connected with each others, and changes in a component of a microbial community may influence the structure of the whole community. This is particularly true for plant-associated microorganisms, which influence on and are influenced by the plant metabolic status .

In order to establish a proper regulation for the use of the many fungicidal substances promoted by industry in sustainable agriculture, fungicide action modes and possible side effects on nonfungal microorganisms must urgently be clarified. Fungicide action modes have never been well classified, and the side effects of these important chemicals are not fully understood. Therefore, fungicide use may have negative impacts that are difficult to predict . In this paper, current knowledge on the action modes of fungicides impacting membranes, nucleic acids and protein synthesis, signal transduction, respiration, mitosis and cell division, and Multisite activity, as well as on their side effects on nontarget organisms will be summarized and organized. The framework emerging from this analysis sheds a much needed light on the possible side effects of the numerous fungicidal products in use and facilitates the assessment of the risks associated with their use. The information summarized here will support the development of efficient agroecosystems where the contribution of naturally occurring bioresources is preserved.

2. Modes of Action and Side Effects of Fungicide Groups

2.1. Effects on the Synthesis of Lipids, Sterol, and Other Membrane Components

The cell membrane is a selectively-permeable wall that separates the cell content from the outside environment. Membranes perform many biological functions in all living cells. They preclude the passage of large molecules, provide the shape of the cell, maintain cell water potentials, and are involved in signal transduction . Negative impacts of fungicide on the membrane of microorganisms were found to alter the structure and function of soil microbial communities.

The structure of lipids, the basic components of cell membranes, was modified by fungicides of the Aromatic Hydrocarbons (AH) group, impacting the functionality of microbial membrane systems. For instance, Dicloran (2,6-dichloro-4-nitroaniline)—an AH fungicide registered in North America, Europe, and South Africa since 1975 for the control of Basidiomycetes, Deuteromycetes, and Rhizopus species —is phototoxic. The cell membranes of treated fungi become sensitive to solar radiation, which then destroys the structure of linoleic acid, a common membrane lipid. Another active AH fungicide ingredient, etridiazole (5-ethoxy-3(trichloromethyl)-1,2,4-thiadiazole), causes the hydrolysis of cell membrane phospholipids into free fatty acids and lysophosphatides , leading to the lysis of membranes, in fungi. Previous research proved that these fungicides have side effects on other soil microorganisms. Dicloran can cause mutation in Salmonella typhimurium by disturbing hydrophobic interactions within the membrane . Etridiazole also reduced the nitrification rate of ammonium-oxidizing bacteria in soil , with possible effect on this component of the soil microbial community and ramifications on its structure and function.

Some fungicides target fungal intracellular membrane systems and their biological functions. A widely used fungicidal compound, acriflavine (3,6-diamino-10-methylacridin-10-ium chloride), increases mitochondrial permeability and releases cytochrome c in fungal cells, repressing plasma membrane receptor activation, disordering proton stream and collapsing the electrochemical proton gradient across mitochondrial membranes . As a consequence, ATP synthesis is decreased leading to cell death. It was also shown that acriflavine could thickened both the peripheral and cross cell wall of the gram-negative bacteria Staphylococcus aureus , suggesting the possibility of nontarget effects of acriflavine on bacterial growth (Table 1).

Action mode Fungicide chemical group Common name Nontarget effects
Lipid, sterol, and other membrane components Lipid Aromatic hydrocarbons Dicloran Mutagen to Salmonella typhimurium
Etridiazole Retards nitrification by affecting ammonium oxidizers
Sterol     Triazoles Triadimefon Long-term inhibiting effects on soil bacterial community
Triticonazole Increases total number of bacteria in soil
Cinnamic acid amide Dimethomorph Impacts nitrifying and ammonifying bacterial activities in sandy soils
Triazole Hexaconazole Impacts bacterial activities related to N cycling
Morpholine Fenpropimorph Inhibit general bacterial activity in wetland
Triazole Propiconazole
Tebuconazole May retard plant-growth-promoting effects of Azospirillum brasilense on its hostplant
Intracellular membrane components Hydrochloride Acriflavine Thickens peripheral and cross cell wall of Staphylococcus aureus
Amino acid and protein synthesis        Glucopyranosyl antibiotic Streptomycin Inhibits amino acid synthesis in bacteria and is neurotoxic to amphibian
Tetracycline antibiotic Oxytetracycline Also used as bactericide
Signal transduction       Phenylpyrroles Fludioxonil Toxic to algae and potential risk to prokaryotes
Dicarboximides Iprodione Affects signal transduction in bacteria
Vinclozolin Inhibits total bacterial growth
Respiration NADH oxido-reductase (Complex I) inhibitors Pyrimidinamines Diflumetorim Unknown
Succinate-dehydrogenase (Complex II) inhibitors Pyridine carboxamides Boscalid May affect growth of prokaryotes
Benzamides Flutolanil
Gxathiin carboxamides Carboxin Inhibits denitrifying bacterial activity in wetland sediment
Oxidative phosphorylation uncouplers 2,6-dinitroanilines Fluazinam Have a potential risk to environmental microorganisms
Dinitrophenyl crotonate Dinocap Inhibits ammonifying bacterial activity and stimulate general bacterial respiration in soil
Mitosis and cell division Inhibitor of spindle microtubules assembly Methyl benzimidazole carbamate Benomyl May affect nitrifying bacteria and arbuscular mycorrhizal fungi
Carbendazim Reduces the diversity of soil bacteria
Phenylurea Pencycuron May affect metabolically activated soil bacteria in short term
Nucleic acids synthesis RNA polymerase I inhibitors Acylalanines Metalaxyl Affects activities of ammonifying and nitrifying bacteria in soil
Oxazolidinones Oxadixyl Unknown
Adenosin-deaminase inhibitors Hydroxypyrimidines Ethirimol Unknown
Phthalonitrile Chlorothalonil Impacts bacterial activities related to N cycling
Multisite activity Dithiocarbamate Mancozeb Impacts bacterial activities related to nitrogen cycling and carbon cycling in soils
Phthalimide Captan Inhibits denitrifying bacterial activity
Dithiocarbamate Thiram
Anthraquinone Dithianon Reduces bacterial diversity in soil
Copper Copper sulfate Reduces the number of bacteria and streptomycetes in sandy soil

Table 1 Action mode and possible nontarget effects of fungicides.

2.2. Effects on Amino Acids and Protein Synthesis

Proteins are the most important building blocks in living organisms. They have various important biological functions such as making up the cytoskeleton, delivering signals among cells, and catalyzing biochemical reactions . Proteins are made of amino acids. Several fungicides interfere with the biosynthesis of amino acids and proteins, affecting the biological functions of impacted organisms.

Streptomycin (5-(2,4-diguanidino-3,5,6-trihydroxy-cyclohexoxy)-4-oxy-3-hydroxy-2-methyl-tetrahydrofuran-3-carbaldehyde), an antibiotic produced by Streptomyces griseus that has long been used as a fungicide , also has bactericidal activity. Streptomycin interferes with amino acid synthesis. In Escherichia coli, application of streptomycin caused misincorporation of an isoleucine molecule in the phenylalanine polypeptide chain associated with 70S ribosomes . Another research with a thermus thermophilus mutant strain suggested that misreading of the genes coding for amino acid synthesis explains the negative effect of streptomycin on bacteria . Furthermore, Perez et al. found that streptomycin could also be a nonselective excitatory amino acid (EAA) receptor antagonist. This antibiotic selectively blocked amino acid receptors in the anterior vestibular nerve fibers of Ambystoma tigrinum, a salamander, suggesting that it could also be toxic to eukaryotes, in addition to fungi and bacteria.

Oxytetracycline ((2Z,4S,4aR,5S,5aR,6S,12aS)-2–4-(dimethylamino)-5,6, 10,11, 12a-pentahydroxy-6-methyl-4,4a,5,5a-tetrahydrotetracene-1,3,12-trione) is widely used in agriculture because of its broad-spectrum antibiotic activity. It is also registered as fungicide in New Zealand and VietNam, according to the information provided by Pesticide Action Network of North America (http://www.pesticideinfo.org/Detail_ChemReg.jsp?Rec_Id=PC38140). Previous research reported inhibitory effects of oxytetracycline on protein synthesis in bacteria through interference with the ternary amino-acyl-tRNA complex binding to the acceptor site of ribosomes , leading to retarded bacterial growth, disordered microbial community structure, and limited microbial ectoenzyme activity in the soil system . Therefore, caution must be taken with the application of oxytetracycline to control fungal diseases, as it is antibiotic and impacts bacteria.

2.3. Effects on Signal Transduction

The fungicide affecting microbial membranes or proteins, as we discussed above, may affect signal transduction, which takes place at the level of membranes and involves the function of certain proteins.

Phenylpyrrole fungicidal ingredient fludioxonil (4-(2,2-difluoro-1,3-benzodioxol-4-yl)-1H-pyrrole-3-carbonitrile), is a nonsymtemic fungicide, also known to interfere with the signal transduction pathways of target fungi . The work of Rosslenbroich and Stuebler revealed inhibition of spore germination, germ tube elongation, and mycelium growth in Botrytis cinerea, by fludioxonil-related interference in the osmoregulatory signal transmission pathway of this fungus. This finding was supported by Ochiai et al. who found that fludioxonil can disturb the CANIKI/COSI signal transduction pathway, leading to the dysfunction of glycerol synthesis and inhibition of hyphae formation in Candida albicans. Recently, Hagiwara et al. reported the inhibiting effect of fludioxonil on a large number of genes involved in a two-component signal transduction system, in filamentous fungi. Impact on this system suggests that fludioxonil may have a nontarget effect on bacteria, as this dualistic signal transduction mechanisms is also reported in prokaryotes .

Effects on signal transduction are also found in dicarboximide fungicides. Iprodione (3-(3,5-dichlorophenyl)-N-isopropyl-2,4-dioxoimidazolidine-1-carboxamide), a contact dicarboximide fungicide widely used in a variety of crops, inhibits glycerol synthesis and hyphal development by cutting off signal transduction , as does fludioxonil. Iprodione can modify the structure of the soil bacterial community, as reported in a recent research . Interference with signal transduction by dicarboximide fungicide vinclozolin ((RS)-3-(3,5-dichlorophenyl)-5-methyl-5-vinyl-1,3-oxazolidine-2,4-dione) caused low growth rate, abnormality, and changes in the productions of hexoses and chitin in treated B. cinerea . Vinclozolin also had inhibiting effects on soil bacterial growth and nitrogen metabolism, in soil systems . The metabolite of this fungicidal compound, 3,5-dichloroaniline, is also toxic and persistent , further suggesting possible impacts of the fungicide vinclozolin on nontarget soil organisms.

2.4. Effects on Respiration

Several fungicides with different modes of action were reported to inhibit microbial respiration. Some are NADH oxidoreductase (Complex I) inhibitors, others are succinate-dehydrogenase (Complex II) inhibitors, cytochrome bc1 (Complex III) inhibitors, and oxidative phosphorylation uncouplers.

Only few fungicides were reported so far to inhibit respiration by affecting Complex I system in fungal mitochondria. Diflumetorim ((RS)-5-chloro-N-{1-propyl}-6-methylpyrimidin-4-ylamine), first registered in Japan in 1997 to control powdery mildew and rust in ornamental plants , inhibits NADH oxido-reductase activity leading to fungal death . Very limited research has investigated the mode of action mode of Complex I inhibitors, which remains poorly understood.

Three widely used Complex II inhibitors, boscalid (2-chloro-N-(4′-chlorobiphenyl-2-yl) nicotinamide), carboxin (5,6-dihydro-2-methyl-1,4-oxathiine-3-carboxanilide), and flutolanil(α,α,α-trifluoro-3′-isopropoxy-o-toluanilide), cause dysfunction of succinate dehydrogenase (SDH) in the tricarboxylic cycle and mitochondrial electron transport chain, inhibiting the activity of Complex II and respiration in fungal cells . Significant yield increases were reported with the use of these fungicides, indicating their effectiveness in the control of fungal diseases . Since Complex II is a common enzyme complex system existing in many eukaryotic and prokaryotic organisms , nontarget effects of Complex II inhibitors on soil bacteria were repeatedly reported , suggesting that cautions must be used with these chemicals.

Whereas some fungicides affect fungal respiration at the level of the enzyme complex system, other fungicides may impact respiration through other targets. Fluazinam (3-chloro-N-(3-chloro-5-trifluoromethyl-2-pyridyl)-α,α,α-trifluoro-2,6-dinitro-p-toluidine) triggers very unusual uncoupling activity in target cells. The metabolic state of their mitochondria was found to be inhibited after exposure to fluazinam, which may be caused by the conjugation of the chemical with glutathione, in mitochondria . Consequently, ATP production is inhibited and downstream cellular metabolisms is interrupted. In fact, the uncoupling activity of eight fluazinam derivatives was recognized , which suggests that fluazinam has complicated ramifications on fungal metabolic pathways and may be toxic in the environment . Another fungicide dinocap (RS)-2,6-dinitro-4-octylphenyl crotonates and (RS)-2,4-dinitro-6-octylphenyl) showed similar action mode to fluazinam, which inhibited ammonifying bacterial activity , suggesting side effects of this fungicide group on bacteria growth.

2.5. Effects on Mitosis and Cell Division

The methyl benzimidazole carbamate (MBC) fungicides are known to impact mitosis and cell division in target fungi . Previous research revealed the inhibitory effects of these fungicides on the polymerization of tubulin into microtubules. These MBC fungicides bind on β-tubulin in microtubules inhibiting their proliferation and suppressing their dynamic instability . Microtubules are the cytoskeletal polymers in eukaryotic cells and, thus, play a vital role in many cellular functions. The application of MBC fungicides suppresses the assembly of spindle microtubules, disturbs the chromosomal alignment at the metaphase plate and microtubule-kinetochore interacions causing chromatid loss, chromosome loss or nondisjunction in target cells , which may also yield side effects on other microorganisms as described below.

Benomyl (methyl 1-(butylcarbamoyl) benzimidazol-2-ylcarbamate) and carbendazim (methyl benzimidazol-2-ylcarbamate), two very popular MBC fungicides widely used in crop production, inhibit mitosis in fungi. They can also influence the beneficial arbuscular mycorrhiza fungi (AMF) and mammalian cells . Although no evidence of a direct effects of MBC fungicides on soil bacteria was reported yet, some research has associated these fungicides to the inhibition of nitrification in soil, a microbially mediated process . The effect of MBC fungicides on bacteria and other soil organisms remains to be clarified.

2.6. Effects on Nucleic Acids Synthesis

Phenylamides (PA) fungicides affect nucleic acids synthesis by inhibiting the activity of the RNA polymerase I system. For example, metalaxyl (methyl N-(methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate), a widely used PA fungicide, inhibits uridine incorporation into the RNA chain . It interferes with nucleic acid synthesis through inhibition of RNA polymerase I activity thus blocking rRNA synthesis at the level of uridine transcription . PA fungicide applications can increase the prevalence of fungicide resistance in pathogen population and yield more fungicide-resistant isolates, as shown by a recent study using AFLP (amplified fragment length polymorphism) and SSR (simple sequence repeats) markers . Fungicides in the PA group must be used with caution, as the side effect of this fungicide on N cycling associated bacteria was reported .

Hydroxypyrimidines fungicides were also reported for their inhibiting effects on adenosine-deaminase. As an example, ethirimol (5-butyl-2-ethylamino-6-methylpyrimidin-4-ol) was reported for its effects on several metabolites such as inosine and adenine nucleotides in barley powdery mildew (Erysiphe graminis f.sp. hordei.) . Ethirimol caused overexpression of adenine phosphoribosyltransferase, which may further break down the balance of the nucleotide pool. Besides, ADAase, which catalyzes the hydrolytic deamination of adenosine, was inhibited by ethirimol. Consequently, production of inosine was ceased, and synthesis of nucleic acid was impaired. The gene responsible for resistance to ethirimol, ethIS, was reported later in Erysiphe graminis f.sp. hordei ; therefore, caution must be taken with the application of hydroxypyrimidines fungicide as fungicide resistance in target populations could be developed by repeatedly fungicide application.

2.7. Fungicides with Multisite Activity

Multisite activity fungicides are widely used in agronomic activities due to the broad spectrum of disease control activity, but may have side effects on other microorganisms due to their multiple biochemical sites impacts. Chlorothalonil (tetrachloroisophthalonitrile), a widely used phthalonitrile fungicide, can block the transformation of alternative special structure of glutathione and reduce enzymes activities which used special conformation of glutathione as their reaction centers. Previous research found that chlorothalonil can influence bacterial growth in soil, which may have ecological consequences on N cycling . Mancozeb (manganese ethylenebis(dithiocarbamate) (polymeric) complex with zinc salt), another Multisite activity fungicide impacting metabolism in target cells, can also affect bacteria involved in both C and N cycling in soil . Other Multisite activity fungicides such as captan (N-cyclohex(trichloromethylthio)-4-ene-1,2-dicarboximide) and thiram (bis(dimethylthiocarbamoyl) disulfide) inhibited the growth of denitrifying bacteria , perhaps due to their nonspecific effects on biochemical compounds which contain thiol in target cells. Besides, copper-based Multisite activity fungicide, such as copper sulfate (copper(II) tetraoxosulfate), inhibited bacteria and streptomycetes growth in soil and may have nontarget effects on other soil microorganisms.

3. Conclusion

Fungicidal compounds may have side effects and impact nontarget soil microorganism. The effects of fungicides on soil microorganisms can be important, as the feedback of the soil microbial community can affect crops growth and production in cropping systems. The relationships existing between fungicides, the soil microorganisms, and other environmental factors are complex and difficult to predict. On the other hand, the multiplicity of fungicides’ modes of action increases the difficulty of evaluating the risks associated with fungicide use. Since it is desirable to optimize the benefit of natural soil biological functions to crop production, understanding fungicides mode of action and impact on metabolism could help us using fungicide more wisely in agriculture.

Acknowledgments

The authors gratefully acknowledge the financial support of Novozymes, Saskatchewan Pulse Growers, and Agriculture and Agri-Food Canada Matching Investment Initiative.

The term biofungicide can have several different meanings, but it is most frequently used to refer to fungicides that contain a microorganism (usually a bacterium or fungus) as the active ingredient. Powdery mildew in roses can be managed with foliar applications of the biofungicide Bacillus subtilis. These microbially-based biofungicides are the focus of this article. Biofungicides can control many different kinds of fungi and water molds, although each separate active ingredient controls only certain pathogens. Some also control bacterial diseases. Virtually all of the organisms used in biofungicides on the market today occur naturally in soil or on plant surfaces, and most are approved for use in organic production.

Advances in fermentation technology have allowed mass production of highly specialized microbes that previously could only be grown in small batches on highly specific substrates, such as on roots infected with pathogens. Consumer demand for organically certifiable pesticides and increased regulatory pressure on older synthetic pesticides, especially in Europe, has Black spot on rose can also be managed with foliar applications of Bacillus subtilis. fostered increased commercial interest in the production of living organisms that can suppress or kill pathogens. For these reasons and also because as natural products biofungicides generally have few negative impacts on health and the environment, the number available will likely continue to increase.

Since microbial biofungicides contain living organisms, their modes of action differ from those of synthetic fungicides. Some of these mechanisms include:

  • Competition: The biocontrol agent is more effective than the pathogen at gathering critical nutrients or space and, therefore, must be in place before disease onset.
  • Antibiosis: The biocontrol agent produces a chemical compound of some type (antibiotic or toxin) that acts against the pathogen.
  • Predation or parasitism: The biocontrol agent directly attacks the pathogen.
  • Induction of host plant resistance: The biocontrol agent triggers a defensive response in the host plant that limits the ability of the pathogen to invade the plant.

Most biofungicides use one or more of the above mechanisms to target only one or a few specific pests. As such, applicators should both read the label and diagnose the problem carefully to insure that the product will be effective. Biofungicides work best when applied preventively. Application after a plant is already infected has little chance of significantly altering the course of the disease for that plant, although it may decrease the ability of the pathogen to move from that plant to other plants, especially if the pathogen has to move through the soil to do so. Thus, an application of biofungicide is not likely to cure an infected plant; but it may protect other nearby plants in the field.

Biofungicides containing Streptomyces or Trichoderma can be used to prevent infection of plants with damping off or root or seed rot pathogens such as Pythium. Although independent testing by university researchers and others has verified some manufacturer claims made for these products, efficacy data for many other products against pathogens on ornamentals is unavailable. For instance, as of early 2014, independent testing has not demonstrated adequate field efficacy of any biofungicide for landscape or agricultural use against Armillaria root rot (otherwise known as oak root rot). However, a number of biologicals have been found effective for control of Pythium, Phytophthora, Verticillium, and other pathogens on a variety of plant hosts. With these types of products, eradication of the pathogen is not the goal and is probably never achieved. Instead, biofungicides rely on a core tenet of the IPM philosophy: keeping pest levels below damaging thresholds and using biofungicides (when necessary) in combination with cultural practices that promote healthy plant growth.

Biofungicides cannot take the place of proper cultural care. They are a valuable tool for keeping a strong plant healthy, but they cannot forestall the inevitable. If your client’s Japanese maples are routinely drowned, allowed to wilt, and then drowned again, adding a biofungicide will not prevent them from contracting Phytophthora if it is present in the soil.

If biofungicides are a useful and environmentally friendly tool in the landscape, why aren’t they more widely used? One reason is that these fungicides rely on living organisms for efficacy, so they must be stored appropriately in order to retain their fungicidal properties over time. However, a more commonly cited reason is that the personal protective equipment needed to apply them is more involved than for some other compounds. Routine exposure to the proteins found in the spray mists of some biofungicides can result in the development of allergic reactions. To keep commercial applicators safe, they must wear NIOSH approved respirators when mixing, loading, or applying biofungicides in agricultural or landscape settings. This may not be immediately obvious when reading the labels, as a quick scan often only shows the following required personal protective equipment (PPE):

  • Long sleeved shirt and long pants
  • Shoes plus socks
  • Waterproof gloves

The respirator requirement is only evident when reading the text following the list. Biofungicides are safe to use as long as mixer/loaders and applicators have and use a respirator as part of their PPE. However, a NIOSH approved respirator requires proper training and fitting in order to be effective.

When used properly and with forethought, biofungicides can be an important part of an IPM program to prevent or mitigate problems with plant pathogens in the landscape. However, nothing can ultimately take the place of proper plant selection and care.

This article was originally published in the April 2014 issue of the UC IPM Green Bulletin. See this and other articles at http://www.ipm.ucdavis.edu/greenbulletin/index.html. /span>

Fungicides for Disease Management in the Home Landscape

Many fungicides are registered for use on commercially produced plants, but only a few are readily available to home gardeners. Most fungicides are not restricted in use or categorized as highly toxic. Yet many of these fungicides are difficult for the average home gardener to obtain in small quantities. Several companies cater to the backyard grower by packaging in small quantities and selling through local variety stores or garden centers. Some of these labels, however, do not specify for “home owners only” and therefore cannot be recommended by Washington master gardeners. These products can still be used by home gardeners. In the Host and Disease Descriptions section of this book, materials available in homeowner formulations and packaging are identified with the symbol H.

Some of the fungicides, such as the sulfur and copper-based products, can be used for growing organic produce. Others, such as captan, tebuconazole, and chlorothalonil, are synthetically produced and not used for organic gardening.

Fungicide names can be very confusing at first. Plant pathologists usually refer to them by their general or common name such as chlorothalonil. Manufacturers and retailers use trade names. For example, chlorothalonil is packaged as Fung-onil, or Multi-Purpose Fungicide for the home market, and as Bravo or Exotherm Termil for commercial markets. The differences are in the formulation (such as a liquid or powder), in how much active ingredient there is per unit of weight (10%, 50%, etc.) and in how it is used (as a spray or drench, for example). Some products, such as a generic flower or fruit spray, may contain more than one type of chemical, usually an insecticide and a fungicide together. The ingredient list on the label will tell you what is in the product.

The label is the law. No matter what anyone else says, always follow label directions. To do otherwise is against the law. However, there are some specific exceptions. If the label says to use a certain amount of product, you cannot use more of it. You can use less, but only if it is still effective at the lower rate. Sometimes a rate range is given so use the higher rate when disease pressure is high and the lower rate when you expect disease pressure to be low. Never use a product on a plant that is not listed on the label. You can use a product to control a disease that is not listed on the label as long as it is effective and the plant is on the label.

Some fungicides work better (stay on the plant longer or spread over the leaf surface) if a spreader sticker is mixed with the solution. It is usually a good idea to add these materials to powders or dusts to be sprayed on plants. Liquid fungicide formulations usually already include such compounds.

Understanding the disease cycle, proper timing, coverage and selection of the right fungicide are needed to get good control using fungicides. Many fungicides work by protecting healthy plant tissues. Captan, copper-based products, chlorothalonil, and sulfurs must be present before fungi begin the infection process. Although myclobutanil and tebuconazole are locally systemic, they must be applied soon after (or before) infection for maximum benefit. None of these fungicides can revive heavily diseased plants.

The following chemicals are listed first by their common name, then by trade names used for the homeowner market. The chemical and its uses are then described.

Captan (Hi-Yield Captan Fungicide, Bonide Captan Fruit and Ornamental)—One of the best all-around, general-purpose fungicides to manage a huge variety of plant diseases, but it is not very good against powdery mildews and rusts. Captan is labeled for ornamentals, lawns, vegetables, and fruit, sometimes alone or in mixes with other pesticides. It works well to manage leaf spots, blights, and fruit and vegetable rots. It is compatible with many other fungicides but cannot be mixed with oils, lime, or strongly alkaline (soapy-feeling) materials. If you use the powdered formulation you will need to agitate (shake, swirl, etc.) the tank to keep it mixed up.

Chlorothalonil (Ortho MAX Garden Disease Control, Bonide Fung-onil, GardenTech Daconil)—This is another good, general-purpose fungicide for many fungal diseases. It is best as a foliar treatment as it breaks down rapidly in soil. It is one of the longer lasting fungicides available so you do not have to spray as often as with other products. Some people are allergic to it and may develop skin rashes if repeatedly exposed. It is labeled for vegetables, fruits, and many ornamentals including shade trees.

Copper-based compounds (Monterey Liqui-Cop and many other names with the word copper in them)—There are many copper products available including copper sulfate, copper octanoate, and copper-ammonium complex. Bordeaux mixture, made by adding copper sulfate and calcium hydroxide to water, was the first fungicide. It still is used in France to manage downy mildew on grapes. It is a highly effective fungicide that stays on the plant surface even after several rains. Usually it is used as a dormant spray as it may burn young tissues. The copper-based products most commonly obtained for the home are labeled for use on many fruits, nuts, ornamentals, and a few vegetables. It controls many fungal and bacterial cankers, galls, blights, and leaf spots.

DMI-type fungicides such as myclobutanil (Spectracide Immunox), propiconazole (ferti-lome Systemic Fungicide, Infuse Systemic Disease Control), and tebuconazole (Bayer Advanced Disease Control)—These products are labeled for use on several ornamental plants and have been used for years to manage all of the important rose diseases. They are very effective against powdery mildews, rusts and many leaf spots. Best used when green foliage is on the plant since they move into plant tissues. Be careful not to overuse these materials as fungi can develop resistance resulting in poor disease control. You may also find other active ingredients in this same class mixed with insecticides (Amdro Rose and Flower Care or Ortho Rose and Flower Insect and Disease Control).

Horticultural and Botanical Oils (Neem Oils such as R-T-U Year-Round Spray Oil)—Some of these are petroleum derived oils while others are from plants. These are effective when powdery mildew has gotten away on you. These products are good eradicants of the fungus if you get excellent coverage of the plant surfaces. Do not use when plants are wet from rain, irrigation or dew otherwise you get poor coverage (since oil and water do not mix). Some oils such as neem oil have a lot of paraffin and may freeze up at low (less than 40°F) temperatures. Just use warm water to get it back in solution. Overall, the neem oils have not done as well for disease management as other horticultural oils in western Oregon.

Soaps (Safer’s Insect Killing Soap and many others)—These are effective on powdery mildew if you use them often and get excellent coverage of the plant surfaces. Also has activity on soft-bodied insects.

Sodium or Potassium Bicarbonates (Bi-Carb Old-Fashioned Fungicide)—Yes sodium bicarbonate is just plain old baking soda. The potassium bicarbonates were developed to prevent salt build up from the sodium form. No, not as good as many of the other products already listed but better than doing nothing. Research data is usually based on adding in oils, which are effective by themselves. Absolutely will NOT control black spot of rose.

Streptomycin (ferti-lome Fire Blight Spray)—An antibiotic produced from a common soil-inhabiting, filamentous bacterium. There is a home label from ferti-lome for use on apples, pears and pyracantha to manage fire blight. Needs to go on at bloom when the weather is expected to be warm and wet. Although it is labeled for rose crown gall you most likely will be better off getting a new rose than following instructions on the label.

Sulfur (Safer Garden Fungicide, Bonide Sulfur Plant Fungicide and many other names with the word sulfur in them)— Elemental sulfur alone is active against powdery mildews, some rusts, leaf blights, and fruit rots. It also is active against mites. It is labeled for fruits, beans, and many ornamentals. Shorter application intervals are needed with sulfur when compared to other products. Sulfur is active as a vapor only within a certain temperature range. If the temperature is over 85°F to 90°F at the time of application, some foliage may burn. Some plants, like ‘Concord’ grapes or apricots, are sensitive to sulfur and will burn at any temperature.

Thiophanate methyl (Bonide Infuse Systemic Disease Control Lawn and Landscape)—This granular form of the chemical is labeled for lawn care but there are only a few diseases that might benefit from its use. It can also be used to manage some root diseases on ornamentals. It needs to be watered within 24 hours after application to move it down into the root zone. From there the roots will pick it up and distribute it through the plant.

Compared to nematicides and insecticides, these fungicides have low toxicity. One would have to eat, drink, or breathe very large quantities to have any immediate or short-term effect on one’s health. Some fungicides, however, have been shown to cause tumors in laboratory animals. When using any pesticide, acutely toxic or not, take several precautions. These are always outlined clearly on each label. Wear protective clothing (gloves, long-sleeve shirt, and long-leg trousers) while mixing or applying the product, keep it out of reach of children and animals, apply it when weather is calm, and clean all equipment, clothes, and yourself after application.

One last point. Many diseases can be managed using several nonchemical management techniques. A combination of techniques, both cultural and chemical, usually works quite well for management of most diseases.

Biological Control (Bayer Advanced Natria Disease Control RTU {Bacillus subtilis strain QST 713} and Monterey Complete Disease Control {Bacillus amyloliquefaciens strain D747}) – Several companies are marketing the use of microorganisms (Bacillus spp.) to combat plant disease pathogens. They make some wide claims about how many different diseases they can control. In general, you will get good management of powdery mildew diseases with these products.

Biological Control (RootShield Home and Garden {Trichoderma harzianum Rifai strain T-22 } – Useful for soilborne fungi that can be very difficult to control. Don’t expect miracles with this but could be used in an integrated program to manage pesky Fusairum diseases on bulb crops.)

Fungicides have become a major component of plant disease management plans for agronomic crops. Fungicides are applied to prevent or slow epidemics of disease caused by fungi. Unlike insecticides and herbicides, which are used to kill insects and weeds, fungicides are applied to form a barrier to protect plant organs from infection.

Performance of fungicide products can be affected by many factors including timing of application, off-label rates, poor product choice for the pathogen of concern (e.g. active ingredient is not effective against the organism), fungicide resistance, etc.

Don’t Forget The Plant Disease Triangle

The plant disease triangle is a diagrammatic view of what it takes for a plant disease to occur. You can think about managing a plant disease by considering how to manipulate certain aspects of the triangle to shrink the center area (a.k.a. to limit plant disease).

One of the best ways to improve the efficacy of a fungicide is to use it in conjunction with other cultural practices. A great model to use when considering an integrated disease management approach is to consider the plant disease triangle. The plant disease triangle demonstrates that it takes a virulent pathogen, a susceptible host, and favorable environment occurring at the same time for the development of a plant disease. If any one of these components is missing a plant disease will not occur. Likewise, if a component of the triangle is manipulated in some way, the magnitude of a disease can be affected.

The host component can be manipulated by using plants that have genetic resistance against the pathogen of interest. Also, managing plant stress and using hybrids/varieties that are well adapted to an area equates to plants that are less likely to be predisposed to a plant disease.

Manipulating the environmental component of the triangle can be much more difficult. However, the environment immediately around a plant (microenvironment) can be changed, to a certain extent. For example, managing soil fertility can provide an environment favorable for plant growth and reduce plant disease. Changing plant population and spacing or reducing irrigation can change the microenvironment and can also reduce plant disease.

The pathogen component can be manipulated in several different ways. Excluding a pathogen from an area is an excellent way to control plant diseases. Using certified pathogen-free seed and cleaning field implements between fields could prevent the introduction of a pathogen to a non-infested field. Eradication can also be applied to pathogens. This strategy can be very difficult because it can be nearly impossible to remove all infested plants and/or soil from an area to completely rid it of a pathogen. Sanitation can be utilized by removing or burying pathogen-infested plant material. As mentioned previously, fungicides are also used to manipulate the pathogen.

Fungicides, Fungicide Mode of Action, and Fungicide Mobility

Fungicide mobility refers to how a fungicide inhibits fungal growth. This is different from mobility which is how the fungicide enters and moves in the plant.

The word ‘fungicide’ implies that a chemical will kill a fungus. This can be misleading as many of the products used to control fungi are actually only fungistatic (meaning they simply inhibit the growth or reproduction of a fungus and are not directly toxic to the organism).

Fungicide mode of action defines how the product actually affects the fungal organism. For instance, the demethylation inhibitor (DMI) fungicide group (contains the triazoles) inhibits a specific enzyme in fungi that plays a role in sterol production. Sterols are necessary for the development of cell walls in fungi. Therefore, the application of DMIs results in abnormal fungal growth, repressed growth, and in some cases death. All fungicides within the DMI group have this same mode of action.

One of the strategies to manage fungicide resistance development is to rotate fungicide mode-of-action. Considering the example of using DMI fungicides above in a proper rotation, the crop manager must choose a fungicide that is not in the DMI group for a subsequent application. This is analogous to a pitcher in baseball. Pitchers don’t typically throw the same style of pitch each time. They rotate fastballs, with screwballs, with sliders, etc. This same approach should be adopted when developing a fungicide program.

Care should also be taken during the development process to identify products with pre-mixed active ingredients in different mode-of-action groups. For instance if a pre-mix product is chosen that contains a Fungicide Resistance Action Committee (FRAC) 3 (DMI compound) and also a FRAC 11 (strobilurin compound) then the next fungicide application should ideally be a product that does not contain either a FRAC 3 or 11 compound.

Fungicide mobility describes how the fungicide enters and moves in the plant. This is different from mode of action which describes how a fungicide inhibits fungal growth.

Fungicide mobility is separate from fungicide mode of action. By understanding mobility and mode of action and how the two work in unison to control a fungus in a crop plant, the better the disease management decision-making process can be. Fungicides have one of two types of mobility: contact or penetrant. Regardless of the mobility, fungicide products work best when applied prior to symptom development and pathogen reproduction (spore production). Applying fungicides close to the onset of an epidemic will yield the best control of diseases caused by fungi.

Contact fungicides are applied to the surface of a plant and do not move into plant tissue. They can be washed from the plant and degrade by exposure to the weather. Therefore, contact fungicides must be reapplied regularly to re-establish protection on previously treated plant organs, or applied to protect new plant growth. Contact fungicides act by forming a protective barrier against fungal invasion. Therefore, they must be applied prior to fungal infection.

Penetrant fungicides can move into plants after being applied to the surface. Due to the movement of the fungicide into the plant, these fungicides are generally considered ‘systemic’ fungicides. This can be misleading as the degree of systemicity can vary among fungicides. Local penetrant fungicides move just short distances, such as into the waxy plant cuticle and remain in that location. Translaminar penetrants can move through the cuticle between cells toward the opposite side of the leaf. Acropetal penetrants are xylem-mobile (xylem elements are the water conducting vessels of plants) and move between cells along a water potential gradient. Acropetal penetrants only move upwards in plants. Systemic penetrants move through cells and follow sugar gradients in plants. Therefore, systemic penetrants can move upward and downward in plants. Very few fungicides are considered systemic penetrants.

Regardless of the level of systemicity, penetrant fungicides have very limited ‘curative’ ability. Penetrant fungicides will only stop or slow infections within the first 24- to 72-hours after fungal penetration. Therefore, best control of fungal infections with penetrant fungicides will be achieved when these products are applied on a preventative schedule.

Fungicide Resistance in Fungi

Fungicide resistance results from genetic adjustment of the fungus, which leads to reduced sensitivity to a fungicide. Genetic mutations in fungi that result in fungicide resistance are thought to occur at low frequency and can be governed by a single gene or multiple genes.

Fungicide resistance development in two populations of fungi. The population on the left has been subjected to fungicide application in a manner to reduce fungicide resistance development. While the population on the right has been subjected to repeated applications of the same fungicide.

Mechanisms that lead to reduced sensitivity to a fungicide can vary, but include a change in the target site, active export of the fungicide out of the fungal cell, breakdown of the fungicide active ingredient, and reduced fungicide uptake.

Fungicide resistance occurs when the frequency of resistant fungal strains in the population outnumbers the fungicide-sensitive individuals. This arises through repeated and exclusive use of fungicides with high-risk for fungicide resistance development.

Selection pressure can be high when repeated fungicide applications are used to control many of the foliar diseases of field crops. Risk of fungicide resistance development is low for seed treatments and soilborne pathogens, which require just one or two applications per season for control.

Practices that Result in Fungicide Resistance

Application of fungicide at the wrong time (ex. after the fungus has begun sporulating) or with inadequate coverage can result in poor control of a pathogen and lead to reapplication thereby resulting in many fungal individuals being exposed to fungicide.

Using inadequate rates can also lead to poor control necessitating the need to apply fungicides frequently, exposing many fungal individuals to fungicide. Excessive application of fungicide where a need is not justified can also lead to higher risk of fungicide resistance.

Other practices that result in exposure of unnecessarily high populations of fungal individuals to many fungicide applications include using susceptible hybrids/varieties, inadequate or excessive fertilization, excessive and/or frequent irrigation, continuous cropping, and poor sanitation.

Fungicide Labels and Efficacy

Below are tables for corn, soybeans, and small grains that are assembled by field crop plant pathologists each year. These tables are based on unbiased data and summarize fungicide efficacy trials across the North Central. Only products that have been tested and the researchers feel there is enough data to draw a sound conclusion are included. If not enough data are available for a product, no rating is offered.

The UW-Extension publication A3878 Fungicide Resistance Management in Corn, Soybeans, and Wheat in Wisconsin provides information on how to avoid fungicide resistance and also lists fungicides labeled for use on corn, soybean, and wheat in Wisconsin.

The UW-Extension publication A3646 Pest Management in Wisconsin Field Crops also lists most pesticides labeled for use in Wisconsin. This publication is updated on an annual basis.

To search further for labeled fungicides or other pesticides in the state of Wisconsin, visit the Wisconsin Department of Agriculture, Trade, and Consumer Protection Pesticide Database Search Engine. This site provides the user the ability to search by crop, chemical, or pest and find products labeled in Wisconsin. The site is updated frequently.

Regardless of state labeling and efficacy rating, remember that timing of fungicide application is critical. A fungicide can be rated excellent for a certain crop, but will fail if applied as a rescue treatment. Fungicides should be used as protectants and applied as early as possible in a disease epidemic. Proper identification of a disease, good record keeping, and being aware of prevailing weather conditions can help the crop practitioner in making good decisions on when to apply a fungicide to maximize its benefit

What About “Plant Health” Benefits from Fungicides?

Break-even scenarios of applying a fungicide to corn.

In many cases a fungicide will not be needed in a particular crop to control a disease. However, a fungicide might be applied to promote “plant health.” Many things should be considered before an application is performed simply for “plant health”:

1. Application of the product can promote fungicide resistance (see above) more quickly for certain pathogens. There might also be negative environmental impacts to applying a fungicide in the absence of disease such as detrimental effects on beneficial insects.

2. The cost/benefit analysis of applying a fungicide might not be good enough to break even. In multi-state corn fungicide trials in the North Central region, the average increase in corn yield when an application of fungicide was applied at the VT-R2 growth stages was just 4.9 bushels. Using the table in the image on the left, the payout on a bushel of corn would need to be in the $7 – $8 range to cover the cost of a $28 – $30 fungicide application.

To view a similar trial performed in Wisconsin in 2011, CLICK HERE TO DOWNLOAD THE REPORT AND DATA. Growers should be careful to consider this break even scenario and weigh other risks like the risk of fungicide resistance development despite just a 4 or 5 bushel increase in yield when applying fungicide in the absence of a disease.

In another recent study, the benefits of fungicide were evaluated on alfalfa. In the study treatments of fungicide were compared to non-treated control plots in trials conducted from 2011-2014. This was done at locations across Wisconsin for alfalfa used for dairy production. Results were variable across locations. However, when a QoI-containing fungicide such as Headline® was used, the average yield increase was 220 lbs. dry matter per acre, per cutting. The return on investment was also investigated. The economics of applying Headline® fungicide can be highly variable depending on alfalfa price and fungicide application costs. If a fungicide application cost is $30 (fungicide plus custom applicator fee) and the hay is sold for $100 per ton of dry matter (TDM), then a 0.30 TDM/acre (600 lbs. dry matter per acre, per cutting) increase in yield is required when applying fungicide to pay for its application. More examples and details can be found by DIRECTLY DOWNLOADING A FACT SHEET BY CLICKING HERE.

Damicone, John and Damon Smith. 2009. EPP-7663 Fungicide Resistance Management. Oklahoma State University Cooperative Extension Service Fact Sheet.

Latin, Richard. 2011. A Practical Guide to Turfgrass Fungicides. American Phytopatholgocial Society 270 pp.

Mueller, Daren S. and Carl A. Bradley. 2008. Field Crop Fungicides for the North Central United States. Ames, IA and Urbana-Champaign, IL: Iowa State University and University of Illinois North Central Integrated Pest Management Center

Since we are well into fungicide application time, below I have listed 10 rules that will help vegetable growers apply fungicides effectively and safely.

  1. Apply fungicides prior to the development of disease. Although many fungicides have systemic (“kick back”) action they will not completely eradicate diseases after they have started. And by the time a single disease lesion is observed in the field, many more lesions too small to observe are already working at your crop. Most systemic fungicides move less than an inch toward the tip of the plant or may just move from the upper to the lower side of the leaf.
  2. Use shorter spray intervals during weather conducive to plant disease. Each plant disease has its own “personality” and thus prefers different weather. However, most plant diseases require leaf wetness. Therefore, during periods of rain and heavy dews, more frequent fungicide applications are a good idea. The normal range of spray applications is every 7 to 14 days. Cantaloupe and watermelon growers have the guesswork taken out of this process with a Purdue University program known as MELCAST. Ask the author for more details by calling (812) 886-0198 or go to melcast.info.
  3. Apply fungicides before a rain if possible. Water is necessary for most fungal spores to infect foliage and for the splash dispersal of spores. Therefore apply fungicides before a rain if it appears that the fungicide will have a chance to dry before the rain. Some fungicides list the rain fastness period on the label. It is not necessary to apply fungicides again after every rain. Most fungicides have a good sticker and will persist through rains pretty well. The MELCAST program takes into account the affect weather has on fungicides.
  4. Know when to alternate fungicides. Systemic fungicides, those with a single mode of action, if applied again and again in sequence, may cause the disease fungi to mutate into a form resistant to the fungicide. Always alternate fungicide applications from one FRAC code (MOA code) number to another. Contact fungicides with a FRAC code of M like chlorothalonil and mancozeb are very unlikely to cause such mutations and therefore may be applied without alternation. Table 29 (page 76) in the Midwest Vegetable Production Guide http://mwveguide.org/ will help growers alternate fungicides.
  5. Timing of fungicide applications is more important than nozzle type and spray pressure. Studies here in southern Indiana as well as by researchers in other areas of the country have found that nozzle type and spray pressure doesn’t make as much difference as we once thought. See the article Spray Pressure and Nozzle Types in issue 596 of the Hotline. In general, the more water one uses per acre, up to about 50 gallons, results in better coverage.
  6. Some diseases cannot be managed by foliar sprays. Problems caused by soil borne fungi or nematodes cannot be controlled with foliar fungicides. Examples of these types of problems would be Fusarium wilt of watermelon or root-knot nematodes of tomatoes. Also, be certain that the problem you observe is really a disease. No amount of fungicide will improve a problem caused by soil fertility. Send a sample to the Purdue Plant and Pest Diagnostic Laboratory to determine the official diagnosis http://www.ppdl.purdue.edu/ppdl/index.html.
  7. Use copper products for bacterial diseases. For the most part, copper products are more effective against bacterial diseases than they are against fungal diseases.
  8. Some diseases require specialized fungicides. Diseases, such as downy mildew and Phytophthora blight may require specialized fungicides. It may be wasteful to apply specialized fungicides all season long for diseases that are not a threat. For example, downy mildew of cucurbits usually does not arrive in Indiana until late in the season.
  9. Double-check the label for details. Rates may vary widely based on label changes and different formulations. While you are checking the rate, also make sure that the crop and disease are on the label. Can this fungicide be applied in the greenhouse? Did you get the rate from the Midwest Vegetable Production Guide for Commercial Growers? Check the label anyway.
  10. Play it safe. Always adhere to the Post-Harvest Intervals, Re-Entry Intervals and Worker Protection Standards listed in the label. No one wants an accident or lawsuit. Besides, the label is the law.

Remember last summer when you found some diseased turf on your grounds that looked similar to the problem you had the year before? After you spotted the problem, you loaded your sprayer with your favorite fungicide and applied the product to your turf. But, to your dismay, the disease persisted, and your turf continued to die. What happened? You’ve used the right product and applied it according to label directions, but your application failed to do the job that it always has done. As you prepared to make another application, the reason your previous fungicide application failed to manage the disease remained a mystery. On certain occasions, fungicide applications fail to provide the desired disease management. It is important to identify the reasons for these failures to prevent them from occurring in the future. This article will help you identify the causes of fungicide-application failures.

Diagnosis and fungicide selection Inaccurate disease diagnosis is the first item you should consider. Your principle concern is whether the decline in turf quality is due to a fungal pathogen or some other cause. Problems commonly misidentified as fungal diseases include insect damage, black layer, chemical injury (such as spills, herbicide damage and fungicide misapplications), nematodes and environmental damage (such as excessive shade, compaction, over-watering and drought). Fungicide applications have little or no effect on non-fungal turf diseases.

Incorrect disease diagnosis also prevents you from selecting an appropriate fungicide. Although any given fungicide will manage a broad spectrum of diseases, it will not manage all diseases. For example, most broad-spectrum fungicides do not control Pythium blight, which requires specific fungicides. Without proper diagnosis, you might select a fungicide that does not control this disease resulting in a quick and permanent demise of the turf. To successfully control a disease with a fungicide, you first have to accurately diagnose it.

Even if your diagnosis is correct, you have to be sure that you select the appropriate fungicide for the job. Be sure to check the label for the specific disease you have identified. In addition to the label, you also can check other sources, such as university field reports, extension bulletins, trade journals, turfgrass-management books and university personnel.

Be cautious about using old material you have in your storeroom. Fungicides stored over 2 years lose their activity and may fail to work when you apply them.

Fungicide loading By improperly loading a fungicide in your sprayer you also can experience treatment failure. First, consider the water you use for your tank mix. Extreme water pH (too acid or alkaline) can reduce fungicidal activity. This is especially true of high pH (greater than 8.0) with fungicides. Optimally, you should use water with a pH of near 7.0 for mixing pesticides. Fortunately, if your water pH is not optimal, you easily can correct it with pH buffers that you add to the water before mixing fungicides in your tank.

For fungicides to effectively manage diseases, you must use them at recommended rates. You also have to be careful that your calculations are accurate. When applicators do make calculation errors, they typically make them in their attempts to determine the correct rate, treatment area or amount of product to add to the tank. Before deciding on a fungicide application rate, be sure to double-check the rate on the label. It’s easy to make simple mistakes such as misreading units (pints per acre, fluid ounces per 1,000 square feet, pounds per acre or dry ounces per 1,000 square feet) or confusing preventive and curative rates. You have to know the treatment area to determine how much fungicide you need to put in the spray tank. The workplace can be hectic, and you easily can be distracted. When this happens while loading fungicides into the sprayer, you may forget how much fungicide you have put into the sprayer. An error in any one of these areas can result in a misapplication. So do not hesitate to check the label before loading the sprayer, and double-check your work.

Mixing multiple fungicides in your spray tank can save you time, but you must be sure they are compatible. Incompatibility can result in the formation of insoluble precipitates in your tank that will prevent you from spraying accurately. Fungicide labels often contain information on mixing compatibility. If the label does not address compatibility, you should test a small volume of the spray mix in a glass jar and allow it to stand for 30 minutes. Look for separation or settling of fungicides in the jar. The order that you add fungicides of different formulations to the tank also may affect compatibility. You should add different formulations of fungicides to the tank in this order: wettable powders, flowables, solubles, powders, surfactants and then emulsifiable concentrates.

Fungicides begin to lose their activity if you allow them to sit too long in a spray tank. After you fill your tank, you might run into an unforeseen emergency, and your application may be delayed. Weather may also delay you from applying. Whatever the cause, you must realize that fungicide activity declines the longer you let your tank-mix sit. The loss of fungicide activity may begin within 12 hours after mixing and is accelerated by poor water quality (such as pond water or high or low pH).

Sprayer calibration and application Perhaps the most common cause of fungicide-application failure is from incorrect sprayer calibration. Using a miscalibrated sprayer is the same as a doctor giving you medication without telling you how much to take. If you fail to calibrate your sprayer you may be applying too much or too little fungicide, which can result in loss of turf from fungicide toxicity or uncontrolled disease. To avoid these problems, remember to recalibrate your sprayer whenever you make modifications to your nozzles, pressure or speed.

In addition to properly calibrating your sprayer, you also should apply the material in the recommended volume of water, at a constant speed and at the recommended pressure. Coverage is especially important for contact fungicides that depend on foliar coverage to provide plant protection. To ensure adequate coverage, use a minimum of 1 to 3 gallons of water per 1,000 square feet. This dilution rate will provide the coverage you need for effective control. It also is important to maintain a constant speed while you spray. Speeding up to “stretch” an application to cover that last half green at the end of the day will only lower the rate of the fungicide you apply. Also, be sure you adjust your spray pressure for the nozzles you use. Excessively high sprayer pressures result in small droplets that are susceptible to drift. After all, the intention is to treat the turf not the air or non-target turf, shrubs and trees. Calibrating and adjusting your sprayer takes time, effort and involves math, but it can save you money, your turf and your job.

The success or failure of a fungicide application is determined by what you do during-and after-the application. To control patch diseases, you often must drench the treated turf with water to move the active ingredient into the crown and root zone where it can protect the plant. Failure to do so typically results in inadequate control. Similarly, you do not want to irrigate turf treated with a contact fungicide until the fungicide has had time to dry on the leaf surface.

Environmental considerations It pays to be aware of weather forecasts when you plan to spray. Unless you are going to drench your application for patch-disease management, you want to avoid spraying when rain is expected. You do not want rain to wash off a contact fungicide you have just applied. The thatch itself is a barrier to an effective fungicide application. The organic matter in thatch acts as a sponge for fungicides. An excessively thick thatch can absorb fungicides you intend to wash into the crown and soil.

Curative applications pose special problems when considering the effectiveness of fungicide applications. By definition, you make these applications after the onset of disease. While the application may have stopped the infection process, the turf is already damaged. Do not expect a curative application to immediately provide healthy turf. If conditions are not favorable for turf growth, do not expect rapid recovery. Curative applications can save turf that is already infected but it is necessary to accept that the turf often needs time to heal after a successful fungicide application.

Resistance Resistance is one of the first things that may come to mind when your fungicide fails to manage disease. It is also one of the least-likely explanations. Fungicide resistance occurs when fungal populations develop that are not sensitive to certain fungicides. Resistance arises when you use the same class of fungicide at high rates over extended periods. The only way to be certain if you have fungicide-resistant pathogens is to have them examined in a lab. Don’t immediately assume that the cause of any fungicide failure is due to fungicide resistance.

Conclusion When your fungicide application fails to provide the disease management you desire, it is important that you examine your fungicide-application practices and identify why the application failed. It often is difficult to recognize your own mistakes, and it may be helpful to ask a colleague or manufacturer’s representative to review your application procedures. The most important thing is to correct the mistake responsible for fungicide-application failure to prevent it from occurring in the future.

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