Brown spot on leaves

Plants With Spotted Leaves: Fungal Leaf Spot Treatments

From indoor and outdoor gardeners alike, one of the most common gardening questions is, Why do my plants have spotted and brown leaves? And while there are many reasons for plain old brown spots, when those spots look like little brown bull’s-eyes, the answer my friends, is fairly simple , organism-wise that is. Those plant leaf spots are caused by one of nature’s most basic organisms: a fungus.

Plants with Spotted Leaves

Fungal leaf spot can be found in your outdoor garden as well as on your houseplant. Spotted leaves occur when fungal spores in the air find a warm, wet, plant surface to cling to. As soon as that microscopic spore gets comfortable in its new home, sporulation (the fungal method of reproduction) occurs and the tiny brown fungal leaf spot begins to grow.

Soon the circle grows large enough to touch another circle and now the fungal leaf spot looks more like a blotch. Eventually the leaf turns brown and falls to the soil where the spores sit and wait for the next available warm, wet, plant surface so the fungal leaf spot process can begin again.

Preventing Plant Leaf Spots

There are a few easy steps you can take to prevent the problem in your garden or on your houseplant. Spotted leaves or the causal fungus need two things to flourish: moisture and poor air circulation.

For your houseplant, spotted leaves can be prevented by watering the soil and not the foliage. Leave enough space between your pots for good air circulation.

In the garden, water in the early morning so the moisture will evaporate from the leaves. Closely packed foliage should be thinned. Always treat pruning and cutting tools with a 1:10 bleach solution after each use. Rake and remove all debris from around your plants before leaf bud each spring.

How to Treat Leaf Spot Fungus

No matter how diligent you are, the day will come when those tiny brown circles on the leaves of your plant so it’s important to know how to treat leaf spot fungus. As soon as you see plant leaf spots, treatment begins.

For houseplants, isolate the pot immediately to prevent the fungus from spreading. Remove any leaf that has been affected. Stop misting.

In the garden, the plant’s leaf spot treatment depends on preference.

For organic treatment, there are several safe and convenient treatments available. Most contain sulfur or copper octanate. Or you can try a more traditional treatment by spraying with a mild solution of bicarbonate of soda (baking soda), using ½ teaspoon per gallon of water.

For those gardeners who have no objection, many all-purpose fungicides are available. Please read the label carefully before applying.

Connecticut State The Connecticut Agricultural Experiment Station

Plant Health Problems
Diseases caused by Fungi:
Powdery mildew, Erysiphe.
White powdery spots or patches develop on leaves and occasionally on stems. Symptoms often first appear on the upper surfaces of the leaves and are usually most pronounced during hot weather. Heavily infected leaves turn brown and shrivel.
Disease can be minimized by avoiding overcrowded spacing of plants and by carefully picking off affected leaves as soon as symptoms are evident. Symptomatic leaves can be placed into a plastic bag in order to avoid spreading the spores of the fungus to other plants. Use of fungicides is usually not necessary. However, applications can be made as soon as symptoms are visible. Among the compounds registered for use in Connecticut are horticultural oil, sulfur, potassium bicarbonate, and thiophanate-methyl. Consult the label for dosage rates and safety precautions.
Leaf spots, Phyllosticta, Glomerella.
Large circular to irregular tan spots develop on leaves, often showing concentric rings of fruiting bodies of the fungus. Affected twigs may also be killed back.
Efforts to maximize plant vigor by fertilizing and watering are helpful. However, watering should be done early in the day to give the foliage a chance to dry before nighttime. It is also helpful to pick and remove symptomatic leaves as soon as they develop. Although not usually necessary, applications of fungicides can be made when new growth emerges in the spring. Among the compounds registered for use in Connecticut are ferbam, mancozeb, and copper compounds. Consult the label for dosage rates and safety precautions.
Diseases caused by Bacteria:
Bacterial leaf spot, Xanthomonas.
Symptoms first appear as pale green, irregular water-soaked spots with yellow or sometimes translucent borders. Spots eventually turn brown to black and are often first evident on lower or inside leaves of densely crowded plantings. Infections on the petioles produce black lesions which crack longitudinally and cause entire leaves to wilt and die. Stem infections may result in yellowing, reduced growth, and dead patches.
This disease can be minimized by improving air circulation by thinning the plants and by avoiding overhead irrigation. Picking and destroying infected leaves is also helpful. Chemical control can supplement other methods for disease management. Among the compounds registered for use in Connecticut are elemental copper, copper hydroxide, and copper sulphate pentahydrate. Consult the label for dosage rates and safety precautions.
Diseases caused by Physiological/Environmental Factors:
Winter injury.
Symptoms of injury appear as tan to brown papery blotches on the leaves. These are usually found at the leaf margins but they can appear anywhere on the leaf. In extreme cases, entire plants may be affected and dead patches subsequently develop in a planting bed. Injury is associated with many factors including extremely cold temperatures, temperature fluctuations and freeze-thaw cycles, and drying winds. English ivy often shows injury from low temperature. Baltic variety is less susceptible and is suggested for use in exposed locations.
This type of injury can be minimized by maintaining plant vigor by proper fertilizing and watering during periods of drought.
Insect Problems:
Black vine weevil, Otiorhynchus sulcatus.
The larvae of this weevil often injure English ivy in nurseries and ornamental plantings by feeding on the roots. The tops of injured plants first turn yellow, then brown, and the severely injured plants die. Leaf notching by adults can be unsightly. The 1/2″ long adult weevil is black, with a beaded appearance to the thorax and scattered spots of yellow hairs on the wing covers. Only females are known. Adults are flightless and feed nocturnally. The legless grub is white with a brown head and is curved like grubs of other weevils. Adults and large larvae overwinter, emerging from May – July. The adults have to feed for 3-4 weeks before being able to lay eggs. Treating the soil with insect pathogenic nematodes may control the larvae and should be the first line of defense for landscape plantings. Acephate and fluvalinate are among the compounds registered for control of this pest in Connecticut, and may be applied when there is adult feeding and before egg laying starts. The usual timing for these foliar sprays is during May, June and July at three week intervals. Insecticide resistance is very common; be aware that adults may appear to be dead following contact with fluvalinate, but may recover from poisoning within a few days. Consult the labels for dosage rates and safety precautions.

Ivy aphid, Aphis hederae.
These are soft bodied, pear-shaped insects, from 1/12″ to 1/4″ (2-6 mm) long, whose identifying characteristic is the presence of cornicles, that look like tailpipes, on the top rear of the body. Antennae are usually shorter than or equal to the body in length. They have piercing-sucking mouthparts and excrete honeydew, which supports black sooty mold. Aphids may be managed by spraying with insecticidal soap or ultrafine horticultural oil, which are among the compounds registered for control of this pest in Connecticut. Aphids on ivy outdoors can be controlled using malathion sprays or imidacloprid can be applied as a soil drench for season-long, systemic control. Consult the labels for dosage rates and safety precautions.

Imported longhorned weevil, Calomycterus setarius.
The grayish adults are about 1/8″ long. They emerge from late June through July and early August. Eggs are laid in the soil, and larvae are present from midsummer until June of the following year. They feed on the small roots of host plants but more often on those of legumes or on organic matter. Both wild and cultivated plants are attacked. Usually, the adults feed on the upper surface at the edge of the leaves and on flowers in sunlight or shade. Host plants include annuals, perennials, shrubs, deciduous trees, and evergreens. Larvae may be controlled by drenching insect pathogenic nematodes around the roots.

Mealybugs, Planococcus citri.
Mealybugs often infest English ivy in houses and greenhouses. White cottony masses appear on leaf surfaces, in leaf axils and sheaths. These insects damage plants by sucking plant sap. Among the compounds registered for control of this pest in Connecticut are insecticidal soap, ultrafine horticultural oil or resmethrin. These products are most effective against crawlers. Because of overlapping life stages in a home environment, multiple applications will be needed to control this pest. Spray needs to contact the insect. Imidacloprid, applied as a soil drench, will provide season-long systemic control. Consult the labels for dosage rates and safety precautions.

Mites.
Houseplants such as gardenia, English ivy and the rubber plant are sometimes attacked by mites such as the twospotted spider mite. Mites are microscopic, have eight legs and spin webs. Most of them like hot, dry conditions and will multiply rapidly when these conditions are present. They feed on the undersides of leaves with their piercing-sucking mouthparts. Symptoms of mite feeding are a yellow stippling of leaves and, when the infestation is severe, webbing may encase the plant. At this point, it’s very difficult to penetrate through the webbing with miticides to obtain direct contact.

Control should begin with keeping the air in the home or greenhouse somewhat humid. Insecticidal soap and ultrafine horticultural oil, which are among the compounds registered for use against this pest in Connecticut, will control mites. Multiple applications may be needed. Hexythiazox or abamectin (a restricted use product) are also effective against this pest. Consult the labels for dosage rates and safety precautions.

Soft brown scale.
This scale insect infests English ivy and many other kinds of plants. The soft scale, Coccus hesperidum, is very thin, oval, and semi-transparent. One remedy is to spray with insecticidal soap or malathion, which are among the compounds registered for control of this pest in Connecticut. These control sprays may need to be repeated if only the crawler stage is controlled. Imidacloprid, applied as a soil drench, will provide season-long systemic control. Consult the label for dosage rates and safety precautions.

White or oleander scale, Aspidotus nerii.
This circular scale infests the leaves and stems of various greenhouse plants including English ivy. This scale is pale yellow, about 1/10″ in diameter and circular in form. Insecticidal soap or disulfoton systemic granules, which are among the compounds registered for control of this pest in Connecticut, can be used, if infestation is severe. In a home or greenhouse situation, all life stages may be present at one time. Insecticidal soap may only kill crawlers, and since there is no residual activity, repeated applications may be required to break the life cycle. Consult the labels for dosage rates and safety precautions.

Houseplant Diseases & Disorders

Houseplants can develop many problems, but most have environmental or cultural causes. Diseases are not common on most houseplants grown indoors because environmental conditions are not favorable for plant pathogens to grow and infect the plants.

Control of diseases begins with prevention. Always buy disease-free plants. Use pasteurized soil when repotting. Before reusing any pots, they should be scrubbed clean and rinsed in a solution of one part bleach to nine parts water to kill any disease organisms present. Take good care of your plants (proper fertilizing, watering and spacing) and check them periodically for disease symptoms.

Diseases

Anthracnose: This disease is caused by the fungi Colletrotrichum and Gloeosporium. The leaf tips turn yellow, then tan, then dark brown. The browning may extend completely around the leaf. The leaves eventually die. Wounding enhances penetration by these fungi.

Prevention & Treatment: Pick off and destroy infected leaves. Do not mist leaves. Sprays of copper soap, chlorothalonil, myclobutanil, or tebuconazole can be used after removing infected plant parts in order to reduce the incidence of future disease. See Table 1 for examples of brands and products. See footnote on Table 1 about spraying houseplants outdoors. Follow label directions for safe use.

Fungal Leaf Spots: Several fungi can cause leaf spots. Symptoms include small, brown spots with yellowish margins on the leaves. Spots may have a concentric ring or target pattern. Small black dots (fruiting bodies of the fungi) may be visible in dead tissue. Sometimes the lesions run together and the entire leaf dies. The fungi survive on dead and decaying plant matter in the soil.

Prevention & Treatment: Remove and destroy infected plant material. Provide good air circulation around the plants. Avoid splashing water on the foliage since this spreads the fungi. Sprays of copper soap, chlorothalonil, myclobutanil, or tebuconazole can be used after removing infected plant parts in order to reduce the incidence of future disease. See Table 1 for examples of brands and products. See footnote on Table 1 about spraying houseplants outdoors. Follow label directions for safe use.

Bacterial Leaf Spots: Plants infected with bacteria have water soaked spots, sometimes with a yellow halo, usually uniform in size and sometimes with a sticky ooze. The spots enlarge and will run together under wet conditions. Under drier conditions the spots do not enlarge but dry out and turn reddish brown, giving a speckled appearance.

Prevention & Treatment: Remove all diseased plant material. Avoid low temperatures, crowding plants, and spraying or splashing water onto the foliage. Sprays of copper soap can be used after removing infected plant parts in order to reduce the incidence of future disease. See Table 1 for examples of brands and products. See footnote on Table 1 about spraying houseplants outdoors. Follow label directions for safe use.

Root Rot & Stem Rot: The fungi Rhizoctonia, Pythium, Botrytis, Phytophthora, Alternaria, and Sclerotinia cause these diseases. With root or stem rot, leaves and stems show a noticeable wilt. Stems may be girdled at or near soil level by a ring of brown or black tissue. Infected roots are brown to black and may be soft. The fungi survive in the soil or on infected plant debris in the soil. Their spores can be spread by wind, splashing water or the moving of infested soil.

Prevention & Treatment: Use sterilized soil and pots. Do not overwater the plants, since too much water increases the occurrence of root rot. If only a few roots are infected, cut out these roots and repot the plant in sterile soil. Fungicides are available, however most indoor gardeners will find that these chemicals probably cost more than a new plant.

Powdery Mildew: The fungus Oidium species causes the formation of a white, powdery growth or dry, brown, papery leaf spots. Initial infections usually come from fungi surviving in dead and decaying plant materials or from airborne spores from wild or cultivated hosts out-of-doors.

Prevention & Treatment: Since the disease develops most rapidly under humid conditions, proper ventilation and not overwatering will help control this disease. Remove severely infected leaves. Sprays of sulfur, chlorothalonil, or myclobutanil can be used after removing infected plant parts in order to reduce the incidence of future disease. See Table 1 for examples of brands and products. See footnote on Table 1 about spraying houseplants outdoors. Follow label directions for safe use.

Cultural/Environmental Problems

Several common problems fall under the category of cultural or environmental problems. There is no control for these problems other than manipulating the plant environment and care program. Over- or under-watering is a major contributor to houseplant decline. Overwatering decreases the amount of oxygen available for root growth and favors development of root diseases. Chronic under-watering results in wilting, leaf curling and death.

Oedema: Oedema is a physiological condition in which rough corky swellings form on the petioles and lower leaf surfaces. Excessive soil moisture and poor lighting with low temperatures predispose plants to oedema. It occurs most often on succulent plants and during the winter. If injury continues, the leaves turn yellow, droop and fall from the plants. Leaves showing symptoms of oedema will not recover, but you can halt the decline of a plant by improving light and watering less often. Repotting to improve soil drainage may also help.

Leaf Drop: Either over- or under-watering can cause leaf drop. Plants in pots that are too small will drop leaves. Some leaf drop occurs when plants are subjected to a significant change in environment, but this leaf drop should only last about three weeks. Chilling the plant can also cause leaf drop. Insects and diseases occasionally cause leaf drop.

Brown Leaf Tips & Edges: Brown leaf tips and margins can be caused by exposure to hot dry air, improper watering, insect feeding, and salt accumulation. White to grey crusty deposits on the soil surface or rim of pots is a sign of salt buildup. (Do not confuse this with the white or yellow mold-like growth of saprophytic soil fungi.) Several steps can be taken to decrease salt buildup and injury:

  • Use rain water when possible to water plants.
  • Drench plants with water periodically to leach some of the salts from the potting soil.
  • Empty water from the saucer under the plant.
  • Do not over fertilize.
  • Remove salt crusts from soil surface and add fresh soil to the pot.
  • Repot plants periodically in new potting soil.

Wilting: Some common causes of wilting are a lack of water, excess water, root rot, too much fertilizer and/or a salt buildup. Overwatering will cause the roots to die from lack of oxygen. Provide drainage, and reduce watering. A pot-bound plant has filled its pot with roots. There is not enough soil to hold the water for all those roots, so the plant wilts. Correct this problem by repotting in a larger pot. Fertilizer and minerals from hard water will accumulate in soil and cause root damage and wilting. Repot in fresh soil.

Yellowing of the Entire Plant: Foliage may become yellow because of too little light, too little fertilizer, insect pests, or mites. Most often yellowing is a symptom caused by overwatering. Check for drainage in the pot, examine the roots and if most are dark, soft and dead, it is better to discard the plant.

Yellowing, Browning & Death of Lower Leaves: This is generally caused by nitrogen or iron deficiency. Pot-bound plants are especially susceptible. Regular application of fertilizer and repotting periodically in fresh soil avoids this problem.

Bud Drop: The premature dropping of flower buds may be caused by lack of fertilization, excessive nitrogen, excessively dry soil, overwatering or spraying with cold water.

Cold Water Spots: Watering with cold water or splashing water on the leaves sometimes causes white or straw-colored spots or patches on the leaves of some plants.

Table 1. Fungicides to Control Diseases on Houseplants.

Fungicide Active Ingredient Examples of Brands & Products % Active Ingredients Pests Controlled
Natural, Less Toxic Fungicides
Copper Soaps Bonide Liquid Copper Fungicide RTU
Natural Guard Copper Soap Liquid Fungicide RTU
0.08% copper
octanoate
Fungal leaf spots,
anthracnose
Sulfur Espoma Earth-tone 3-in-1 Disease Control – Kills Fungus, Insects & Mites RTU
Ortho Insect, Mite & Disease 3-in-1 RTU
0.20% Sulfur
0.01% Pyrethrins
Powdery mildew
Contact & Systemic Fungicides
Chlorothalonil Bonide Fung-onil Multi-Purpose Fungicide RTU
Ferti-lome Broad Spectrum Landscape & Garden Fungicide RTU
0.087% Chlorothalonil Fungal leaf spots, powdery mildew,
anthracnose
Myclobutanil Spectracide Immunox 3-in-1 Insect & Disease Control for Gardens RTU 0.012% Myclobutanil
0.02% Permethrin
Fungal leaf spots, powdery mildew, anthracnose
Tebuconazole Bayer Advanced 3-in-1 Insect, Disease & Mite Control RTU 0.015% Tebuconazole
0.012% Imidacloprid
0.014% Tau-
Fluvalinate
Fungal leaf spots, anthracnose
RTU = Ready to Use (a pre-mixed spray bottle)
Note: Spraying of houseplants is most safely done outdoors during mild temperatures. Once plants are dry, they may be brought back indoors. The other active ingredients: pyrethrins, permethrin and imidacloprid are insecticides; tau-fluvalinate is a miticide.

Why do my maple leaves have spots?!

Homeowners with maple trees are calling the Michigan State University Extension Lawn and Garden Hotline concerned about numerous spots appearing on the leaves. After teasing out additional information from callers, most folks are seeing symptoms of a fungal disease known as tar spot. The disease is caused by several fungi in the genus Rhytisma and infects silver, sugar, red and Norway maple as well as their relative, box elder.

Tar spot is one of the most readily visible and easiest maple diseases to diagnose. It’s also one of the least damaging ailments on its host. The first tar spot symptoms usually show up in early summer as small (less than 1/8 inch diameter), light-green to yellowish-green spots. The spots enlarge and color intensifies as summer progresses. Small, black, tar-like raised structures form on the upper surface within these yellow spots. The black spots continue to grow in diameter and thickness to the point where it looks like someone splashed tar on the leaves. (This is the time when homeowners become rather alarmed.) Symptoms tend to be more common on trees growing in moist, sheltered locations.


Early symptoms on Norway maple. Photo credit: Mary A. Wilson, MSUE.


Current symptoms on Norway maple. Photo credit: Mary A. Wilson, MSUE.


Silver maple leaf infected with tar spot. Photo credit: Steven Katovich, Bugwood.org.

Impact

This disease is usually a cosmetic problem and does not affect the long-term health of the tree. Heavy infections can cause premature leaf drop – a circumstance that causes great consternation to homeowners because lawns are littered and must be raked before autumn typically arrives.

Management

Since tar spot fungi overwinter in fallen leaves, the most effective management technique is to rake and destroy leaves in the fall. This will reduce the number of overwintering “spots” (containing the fungal reproductive structures) that can infect new leaves the following spring. Neighbors should also rake and destroy infected leaves to be effective. Mulching leaves will destroy many of the spots before they mature, but the mulch pile should be covered or turned before new leaves begin to emerge in the spring.

Applications of fungicides are possible when high levels of infection become unacceptable, but control of tar spot is challenging, especially on mature maples. In addition, if others in a neighborhood setting are not managing the disease on their trees with fungicides or proper sanitation, the act of spraying may be a waste of time and money.

  • Gardening in Michigan

Tomato Plant Diseases and How to Stop Them

Feb 21, 2017

Written by Kayla Harless, People’s Garden Intern

Almost everyone who gardens grows tomato plants. We are passionate about our tomatoes and savor that ripe, fresh fruit. However, several diseases love our tomato plants just as much as we do. The People’s Garden Workshop topic this week was tomato blights and spots, and Dr. Martin Draper, a plant pathologist through the USDA National Institute of Food and Agriculture, taught us how to identify them and what we can do to treat and prevent them.

He discussed in detail three pathogenic diseases: septoria leaf spot, early blight, and late blight. Don’t let the names early blight and late blight mislead you, they can appear at any time during the year. Septoria leaf spot is characterized by small, dark circular spots that often have yellow halos around them; they appear on the lower leaves of the plant first. Early blight can set in the stems and leaves, and is identified by legions with target-like rings. Late blight affects large portions of the leaves. It looks white and fuzzy on the underside of the leaf, and destroys crops quickly. Early and late blight affect potatoes as well, in fact, late blight caused the Irish potato famine.

These diseases can be spread many ways, and knowing what they are can supply simple solutions. Moisture, especially on the leaves, provides great conditions for the spores of these diseases to make themselves at home. Watering at the base of the plant can help prevent this; if you do use a sprinkler system or similar method to water your tomatoes, do so in the morning to allow the plant an opportunity to dry throughout the day. It is also recommended to stake your tomato plants instead of caging them, and space them appropriately. This way, the space will make it slightly more difficult for diseases to spread quickly, and the airflow will keep the plants dry. Keep a watch on your garden, and pluck any leaves that show signs of disease and take out infected plants.

Some fungicides can be very effective; however, it is important to follow the label. A fungicide intended for different plants, not vegetables, won’t make a difference and may cause problems. If you garden organically, adding compost extracts or teas can be a treatment. To create a solution that prevents and treats disease, add a heaping tablespoon of baking soda, a teaspoon of vegetable oil, and a small amount of mild soap to a gallon of water and spray the tomato plants with this solution. This needs to be reapplied regularly to maintain its efficiency. Garden clean-up is another preventative key, as the diseases’ spores can overwinter on plants left in the garden from the previous year.

There are many USDA extension offices throughout the country and research facilities on every land-grand university, so if you have further questions or concerns about tomato diseases feel free to contact one of these places.

Dr. Martin Draper looked at samples the workshop attendees brought from their gardens and gave suggestions as to what can be done to bring the plants back to health. Category/Topic: Initiatives Research and Science Tags: Dr. Martin Draper NIFA plant pathology

Write a Response

S. Snyder Jun 30, 2013

When our tomato plants start producing fruit the tomato starts to turn black on the bottom. Does anyone know what the problem is?

Jill Jun 25, 2014

It is usually due to a lack of calcium in the soil – called blossom end rot.

Phungula SM Mar 03, 2015

What is the cause of Septoria leaf spot? I am Plant Pathology undergraduate student.

Ben Weaver Mar 04, 2015

@Phungula SM – thank you for asking. This is a complex question that is dependent on the crop and the origin of the problem. Septoria species fungi cause leaf spot diseases on many host plant species. Septoria fungi are typically residue-borne organisms that survive through periods of adverse environment on infected plant material. They reinfect susceptible green plant tissue during wet periods and the spores of the pathogen are spread from the residue by rainsplash. Septoria spp. causes important disease of celery where the disease is called late blight (Septoria apii/ S. apiicola); wheat – where it causes Septoria blotch (S. tritici); tomato – where it causes Septoria leaf spot (S. lycopersici). There are also Septoria leaf spotting diseases of blueberry, soybean, brambles, several flowering composites, and many, many other plant species.

Ken Jun 26, 2018

What do you think of using commercial copper sprays to treat blight?

You probably won’t be able to avoid Septoria leaf spot altogether. It is very widespread and, given the ideal conditions, it will try to take hold in your garden. However, there are some precautions you can take to lower the likelihood that Septoria leaf spot will occur.

  • Use disease-free seed. There’s no evidence that it is carried by seeds, but err on the safe side and don’t save seed from infected plants. Thoroughly processing the tomato seeds you are saving will also help rid the seeds of lingering diseases.
  • Start with a clean garden. Dispose of all affected plants. The fungus does not remain in the soil, but it can over-winter on the debris of diseased plants. So it’s important to dispose of all the affected plants far away from the garden and the compost pile. Keep in mind that it may have spread to your potatoes and eggplants, too.
  • Avoid overhead watering. Water aids the spread of Septoria leaf spot. Keep it off the leaves as much as possible by watering at the base of the plant only. Of course, it’s impossible to keep the rain off your plants, but every little bit helps.
  • Provide room for air circulation. Leave some space between your tomato plants so there is good airflow. Stake them so that they are not touching the ground and not all bunched together. Good air circulation is especially important during damp and rainy periods.
  • Mulch below the plants. A layer of mulch will prevent spores on the ground from splashing up onto the lower leaves.
  • Plant next year’s tomatoes in a different section of your garden. In small gardens, it’s not always practical to rotate your crops, so good clean up and sanitation become even more important.

Leaf spots may mean a fungal disease

As the hot weather abates just a bit, gardeners find themselves back in the landscape only to find an outbreak of spots on their plants. Hot, humid and rainy weather are perfect conditions for the development of fungal diseases.

One of the most common leaf spot diseases seen in the landscape during late summer is Cercospora leaf spot. While it affects many different landscape plants, it is most commonly seen on hydrangeas. It affects smooth, panicle, oakleaf and bigleaf types of hydrangea. However, this year, there have been numerous occurrences on crape myrtles.

Symptoms

On bigleaf hydrangea, the spots are small, circular and have a purplish halo surrounding them. The centers of these spots eventually turns tan to light gray in color. In contrast, the leaf spots on oakleaf hydrangea appear angular in shape and are dark brown in color. Leaves that are severely affected often become a yellow-green color.

Initial symptoms on crape myrtles are the appearance of dark brown spots that develop first on the lower leaves and progress upward in the canopy from mid-summer through fall. Infected leaves develop a yellowish to orangey-red coloration because of the production of a toxin by the pathogen. These leaves then fall prematurely, particularly in highly susceptible varieties.

Numerous infectious spores are produced in the center of each fungal spot. These spores can be spread by wind, splashing water and can hitch a ride on pruning tools. Frequent late summer rain showers will not only greatly increase the rate of disease spread, but also intensify the level of leaf spotting and defoliation. Extended periods of drought will usually suppress disease development and spread.

Although this disease can be visually alarming, it is generally an aesthetic problem for homeowners because the disease rarely kills the plant. However, if this disease is severe, it can reduce the overall plant vigor by repeated defoliation.

Control strategies

There are some fungicides available to help manage Cercospora leaf spot, but for the homeowner, disease management with fungicides is often not warranted because symptoms usually occur so late in the season. This does not mean, however, that you should ignore the problem. Once this disease is found in a planting, yearly outbreaks are likely to occur.

The fungus easily survives on fallen leaves. Sanitation is perhaps the most important tool in disease management. Be sure to remove and destroy these leaves to help prevent future infections and disease outbreaks.

Another important cultural practice includes surface watering. Because moisture on the leaves allow disease spores to germinate, avoid getting the leaves wet with overhead irrigation. Also be sure to apply enough nitrogen to maintain a moderate growth rate. It is also helpful if your plants are not crowded. Good air circulation permits the leaves to dry quickly after a rain, which helps prevent leaf spot diseases.

This fungal disease creates circular leaf spots. The spot’s center will turn tan or light gray.

However, the use of fungicides may be justified for high-value landscape plantings that develop severe cases of the disease each year. Products containing chlorothalonil, myclobutanil or thiophanate-methyl are recommended. For effective control of Cercospora leaf spot with a fungicide, begin applications when spotting of the leaves is first seen and continue applying that treatment as needed. Be sure to follow label directions!

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When we launched Pistils Rx a few weeks back, we got an outpouring of emails and comments from our readers asking plant questions. Thank you all for your photos and for describing your issues in such detail! Of the questions we received, no issue popped up quite as frequently as houseplant leaves turning brown.

There are a multitude of reasons why your houseplants leaves might be turning brown, and just as many ways that browning can present (entire leaves, leaf tips, leaf sides, inside the leaves, lower leaves, upper leaves…). And yes, you guessed it – each of these symptoms can have a myriad of causes, depending on the plant species and how it’s been cared for.

That said, there are a few good rules of thumb to help you diagnose the cause of houseplant leaves turning brown. We’ll use the photos you sent to us and show you what to look for when diagnosing why your indoor plant’s leaves are turning brown.

5 Reasons for Houseplants Leaves Turning Brown

  1. Not enough water (or too much!)

    Check out the dry stems and brown lower leaves on the tradescantia ‘wandering jew’ in the photo, above. Dry, brown, crispy, and browning starts at the lower leaves. If this looks familiar, you may well be under-watering your plant. Alternately, over-watering can sometimes present in the same way. This is because overwatering damages roots, inhibiting their ability to take in water and causing symptoms of thirst

    Solution: Trim off brown leaves; they’re not coming back. If entire stems have dried, prune them off and try propagating the ends of pruned stems with stem tip cuttings. Water regularly, and thoroughly, taking care not to over-water.

  2. Normal aging or Humidity is too low

    Some plants drop lower leaves as the plant matures. This is especially true on ferns (like this asplenium) and some philodendron species. Just prune the old leaves away, and you should be good to go!

    Remember; your tropical plants are, in fact, native to the tropics. The tropics are wet and the air is humid! Some houseplant leaves turn brown and crispy when the air in our homes is too dry. This is especially true if your plant is getting a lot of direct sun, or during the winter when heaters are running and drying out the air.

    Solution: Move plants away from heaters. Try setting them on a dish full of pebbles, and putting a layer of water in the pebbles. This helps create ambient humidity. Trim off any dried out leaves.

  3. Browning leaf tips
    Browning leaf tip tips are as common as they are challenging to diagnose. This physiological condition can be caused by tainted water, erratic watering (too much, too little, or a combination of both), overfeeding, or a combination of all of these. Plants with long, strappy leaves, like dracena, spider plants and calathea (see photo) are often affected, because water has to make the long trip to keep the cells at the leaf tips well hydrated.

    Solution: Evaluate your plant care regimen and see which of the above factors is the most likely culprit; adjust as necessary. If the brown tips are causing you grief, trim them back with a pair of clean scissors. Take care to cut just outside the line where the green turns brown; otherwise, you can cause a new brown line to form.

  4. Too much fertilizer

    Browning around the sides and tips of leaves is often caused by too much fertilizer. Your plant might also show symptoms of thirst. This is because over-fertilizing damages roots, which in turn affects their ability to take in water, making them act thirsty. Most plants don’t need much (or any) fertilizer over the winter months, and this is when it tends to accumulate and cause leaves to turn brown (like on this natal mahogany, which was fertilized every other week). You might also notice a crusty layer of fertilizer build-up on the surface of the soil.

  5. Pests and disease

    This is a tough one, and will be getting its own Pistils Rx post in the future. There are many pests that can infest your houseplants, with scale, mealybugs, spidermites and aphids being some of the most common. Fungus can also attack the roots of your plants, making it show the signs of over-watering (leaf browning and yellowing!). Most pests can be seen with the naked eye, but keep an eye out for brown bumps, white fuzz and webbing on and under your plant leaves. Brown spots in the leaf centers are often caused by pests or diseases.

    Solution: As challenging as it may be, consider disposing of truly infested plants in order to save the rest of your indoor garden. They spread quickly! That said, we use insecticidal soap and neem oil to treat minor pest and fungal problems. Prune back any infested branches of your plant and clip off unsightly brown leaves. Allow the plant to rest and recover and continue to check on the pest issue regularly.

Are your plant leaves turning brown, but it doesn’t sound like any of the above? Write to us in the comments, and we’d be happy to try and help diagnose your plant problem! We have lots more in store for Pistils Rx, and we want to hear from you and see your photos! Submit them to us by sending an email, with photos, to [email protected]

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