Mold on tomato leaves

What Is Tomato Leaf Mold – Managing Tomatoes With Leaf Mold

If you grow tomatoes in a greenhouse or high tunnel, you are more likely to have problems with leaf mold of tomato. What is tomato leaf mold? Read on to find out the symptoms of tomatoes with leaf mold and tomato leaf mold treatment options.

What is Tomato Leaf Mold?

Leaf mold of tomato is caused by pathogen Passalora fulva. It is found throughout the world, predominantly on tomatoes grown where the relative humidity is high, particularly in plastic greenhouses. Occasionally, if conditions are just right, leaf mold of tomato can be a problem on field grown fruit.

Symptoms start as pale green to yellowish spots on upper leaf surfaces that

turn a bright yellow. The spots merge as the disease progresses and the foliage then dies. Infected leaves curl, wither and often drop from the plant.

Flowers, stems and fruit may be infected, although usually only leaf tissue is affected. When the disease does manifests on the fruit, tomatoes with leaf mold become dark in color, leathery, and rot at the stem end.

Tomato Leaf Mold Treatment

The pathogen P. fulfa can survive on infected plant debris or in the soil, although the initial source of the disease is often infected seed. The disease is spread by rain and wind, on tools, clothing and via insect activity.

High relative humidity (greater that 85%) combined with high temperatures encourages the spread of the disease. With that in mind, if growing tomatoes in a greenhouse, maintain night temps higher than outside temperatures.

When planting, use only certified disease-free seed or treated seed. Remove and destroy all crop debris post-harvest. Sanitize the greenhouse between crop seasons. Use fans and avoid overhead watering to minimize leaf wetness. Also, stake and prune plants to increase ventilation.

If the disease is detected, apply a fungicide according to the manufacturer’s instructions at the first sign of infection.

Leaf Mold in Tomato

Leaf mold (formerly Fulvia fulva) has been confirmed in field-grown tomatoes in Cape May County.

Leaf mold occasionally appears in high tunnel or greenhouse tomato production in New Jersey. However, under ideal conditions the disease will develop in field-grown crops. The fungus will cause infection under prolonged periods leaf wetness and when relative humidity remains above 85%. If relative humidity is below 85% the disease will not occur. The pathogen can survive (overwinter) as a saprophyte on crop debris or as sclerotia in the soil. Conidia (spores) of the fungus can also survive up to one year in the soil.

Symptoms of leaf mold on infected tomato plant. Note bright yellow leaves and olive-green spores developing on undersides of leaves.

Leaves of infected plants will develop pale-green or yellow spots that are distinct. A dense, olive-green to brown spore mass will develop on the undersides of infected leaves.

Management of leaf mold begins with recognizing early symptoms, applying preventative fungicides, and removing all infected plant material from the field, greenhouse, or high tunnel, and crop rotation. Protectant fungicides such as chlorothalonil used in weekly protectant spray programs will help control leaf mold. For organic growers, regular copper applications may help to suppress the disease.

Cultivars with resistance to leaf mold have been developed. A nice write up with more information on leaf mold and cultivars with resistance by Dr. Beth Gugino, vegetable pathologist at Penn State, can be found at Leaf Mold on Tomato: Host Resistance is a Management Option.

How to identify and control tomato plant disease

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Tomato growers are a passionate bunch. Some of us spend long hours combing over seed catalogs and nursery benches full of plants to select the perfect tomato varieties for our garden. We plant, tend, prune, fertilize, stake, and otherwise care for our tomato plants with a dedication rivaled only by our dedication to our human family. But, even with all that care and attention, sometimes a tomato plant disease strikes our garden. Today, let’s review some of the most common tomato plant diseases and discuss ways to prevent and manage them, without resorting to synthetic chemicals for control.

Types of tomato diseases

Unfortunately, there are several pathogens that can cause tomato plant disease. I’m going to introduce you to several specific tomato diseases later in this article, but before I get to that, it’s important to talk briefly about the different types of pathogens and how to prevent them from striking your garden in the first place.

Some tomato disease pathogens are fungal organisms while others are bacterial or even viral. Different regions of North America are affected by different tomato pathogens, and rates of infection are dependant on many factors, including wind patterns, temperature, humidity, varietal resistance, and plant health, to name just a few. It’s important to remember that tomato plants that are healthy and properly cared for will often show more resistance to tomato plant disease, so ensuring your tomato crop has ample moisture and healthy, fertile soil is a must.

Preventing tomato diseases is a must, if you want to have productive plants.

Preventing tomato plant disease

Other than making sure your tomato plants are happy and healthy, there are a few other things you can do to help prevent tomato plant diseases. Here are nine tips to get you started on the road to disease-free, productive tomato plants:

  1. Rotate your crops. Since many tomato pathogens live in the soil, plant tomatoes in a different spot in the garden each year.
  2. Pinch off leaves with any signs of disease immediate and dispose of them in the trash to keep a possible infection from spreading.
  3. Don’t work in the garden when tomato foliage is wet or you may inadvertently spread pathogens from plant to plant.
  4. Choose disease-resistant varieties when selecting which types of tomatoes to grow.
  5. Remove all diseased tomato plant debris at the end of the growing season and burn it or toss it in the trash. Do not put diseased foliage in the compost pile.
  6. Provide adequate air circulation around each plant. Here’s our guide to spacing tomatoes properly.
  7. Mulch your tomato plants well at the start of the season. Two or three inches of compost, leaf mold, straw, or hay serves to keep soil-dwelling fungal spores from splashing up onto the lower leaves when it rains.
  8. Try to keep the foliage dry whenever possible. Hand irrigation or soaker hoses allow you to target the water on the root zone. The splash from overhead sprinklers can spread disease and wet foliage promotes fungal issues.
  9. Disinfect the empty pots if you grow your tomatoes in containers, using a 10% bleach solution at the end of the growing season and replace the spent potting soil with a new mix every spring.

    Follow every prevention tip you can to keep your tomato plants from being ravaged by diseases like this one.

6 Common tomato plant diseases

Despite your best efforts at preventing tomato diseases, they may still get a foothold in your garden from time to time. Here’s the low-down on six of the most common tomato plant diseases with information on identifying, preventing, and managing each of them.

Early blight

Identify: This common tomato plant disease appears as bulls-eye-shaped brown spots on the lower leaves of a plant. Often the tissue around the spots will turn yellow. Eventually, infected leaves will fall off the plant. In most cases, the tomatoes will continue to ripen, even as the disease symptoms progress up the plant.

Prevent: The early blight pathogen (Alternaria solani) lives in the soil and once a garden has shown signs of the early blight fungus, it’s there to stay because the organism easily overwinters in the soil, even in very cold climates. Fortunately, most tomatoes will continue to produce even with moderately severe cases of early blight. To prevent this tomato fungal disease, mulch plants with a layer of newspaper topped with untreated grass clippings, straw, leaf mold, or finished compost immediately after they are planted. This mulch forms a protective barrier, preventing the soil-dwelling spores from splashing up out of the soil and onto the plant.

Manage: Once the fungus strikes, organic fungicides based on Bacillus subtilis or copper can help prevent or stop the spread of this tomato plant disease. Bicarbonate fungicides are also effective (including BiCarb, GreenCure, etc).

Early blight often begins as irregularly shaped, bulls-eyed brown spots on the lower leaves of a tomato plant.

Fusarium wilt

Identify: The pathogen that causes Fusarium wilt (Fusarium oxysporum) is generally more common in warm, southern regions where this tomato plant disease can wipe out entire fields. Symptoms include drooping leaf stems. Sometimes an entire branch may wilt, often starting with the lower portion of the plant and then progressing upwards until the whole plant collapses. To confirm an infection, cut the main stem of the plant open and look for dark streaks running lengthwise through the stem. Sometimes there are also dark cankers at the base of the plant

Prevent: The spores of this tomato plant disease live in the soil and can survive for many years. They’re spread by equipment, water, plant debris, and even people and animals. The best method of prevention is to plant resistant varieties if you’ve had trouble with Fusarium wilt in the past. Also disinfect tomato cages and stakes with a 10% bleach solution at the end of every season.

Manage: Once this tomato plant disease strikes, there’s little you can do to control it. Instead, focus on preventing it for future years. Soil solarization can help kill fungal spores in the top few inches of soil, and crop rotation is key. There are also several biological fungicidal drenches that can be applied to soil (look for one based on the bacteria Streptomyces griseoviridis called MycoStop® or a granular one based on the fungus Trichoderma virens called Soil Guard®). These products may help prevent the infection from colonizing the roots of future crops.

Late blight

Identify: Late blight (Phytophthora infestans) is among the most destructive tomato plant diseases. Thankfully, it’s not very common, especially in the north where it doesn’t survive winter’s freezing temperatures without a host plant. Late blight is caused by a fungus, and it creates irregularly shaped splotches that are slimy and water-soaked. Often, the splotches occur on the top-most leaves and stems first. Eventually, entire stems “rot” on the vine, turning black and slimy. There may also be patches of white spores on the leaf undersides. In the north, the pathogen overwinters in buried potato tubers. In the south, it easily survives the winter.

Prevent: The spores of this disease are fast-spreading, moving on the wind for miles. If you live in the northern half of the continent, do not purchase potatoes and tomatoes that were grown in the south as you may inadvertently introduce late blight spores to your garden. This is not a common pathogen, but if late blight is reported in your area, there is little you can do to prevent the disease because the spores spread so rapidly. Plant only locally grown plants to help keep the pathogen out of your area.

Manage: Once late blight strikes, there is little you can do. Tear out the plants, put them in a garbage bag, and throw them out to keep the disease from spreading. Organic fungicides based on Bacillus subtilis are somewhat effective in preventing this tomato plant disease when it’s first discovered in your area.

Late blight is an extremely difficult tomato disease. It’s not common, but it is troublesome.

Septoria leaf spot

Identifiy: Appearing as tiny, round splotches on the leaves, this tomato disease (Septoria lycopersici) typically starts on the lowest leaves first. The spots have dark brown edges and lighter centers, and there are usually many spots on each leaf. Infected leaves eventually turn yellow and then brown, and fall off.

Prevent: Remove diseased tomato plants at the end of the season to prevent the spores from overwintering in the garden. Cut off and destroy infected leaves as soon as you spot them and disinfect pruning equipment before moving from one plant to another.

Manage: Organic fungicides based on copper or Bacillus subtilis are effective against septoria leaf spot, especially when used as a preventative measure.

Septoria leaf spot is a tomato disease that produces splotches and spots on the foliage and can reduce yields.

Southern bacterial wilt

Identify: Unfortunately, once present, Southern bacterial wilt (Ralstonia solanacearum) is a tomato plant disease that spreads like wildfire. It’s soil-borne, but the bacteria that cause this tomato disease can travel by soil, water, plant debris, and even on clothes, tools, and skin. It’s naturally found in tropical regions and greenhouses, but it can arrive in the garden via infected plants that were purchased from other areas. Initial symptoms include the wilting of just a few leaves on a plant, while the rest of the foliage appears healthy. Over time, more and more leaves wilt and turn yellow until all the leaves succumb, though the stem remains upright. Slimy ooze threads out of the cut stems, and when they’re placed in water, milky streams of bacteria stream out of the cut.

Prevent: Southern bacterial wilt is soil borne and can survive for long periods in the soil on roots and plant debris. Like many other tomato diseases, it favors high temperatures and high humidity. The best way to prevent this disease is to purchase and plant only locally grown plants, or grow your own plants from seed. Southern bacterial wilt is more common in warmer regions, but has been found in Massachusetts and other northern regions as well.

Manage: There is no cure for this disease. Once confirmed, immediately remove infected plants and discard them in the trash.

Verticillium wilt

Identify: This fungal disease is caused by several soil-borne pathogens (Verticillium spp.). When present in a tomato plant, they block the vascular tissue in the plant and cause the leaves and stems to wilt. Symptoms progress slowly, often one stem at a time. Eventually, the entire plant yellows and withers. To confirm diagnosis, cut through the main stem of the plant and look for dark brown discoloration inside. Verticillum wilt is most problematic in late summer.

Prevent: Verticillium fungi can survive for many years in the soil and on plants. They thrive in slightly cooler summer temperatures (between 70 and 80 degrees F). Plant only resistant varieties.

Manage: Once verticillium wilt occurs, there’s little you can do to control the current year’s infection. Instead, focus on preventing this tomato plant disease in future years. Soil solarization will help kill the fungal spores in the top few inches of soil. Practice crop rotation: do not plant other members of the same plant family in that same planting area for at least four years after the infection.

Many soil-borne tomato diseases aren’t as problematic when the plants are grown in containers. Check out this video introducing 5 of the best varieties of tomatoes for growing in containers.

With an eye toward prevention and employing early management practices as soon as a disease is spotted, you’ll be able to grow a terrific crop of tomatoes each and every season.

For more on growing great tomatoes, check out the following posts:
Our favorite cherry tomato varieties
The best heirloom tomato varieties
5 Tips for growing tomatoes in raised beds
How to grow tomatoes from seeds
Top tomato varieties from the experts

Do you have a favorite tomato variety you grow every year? We’d love to hear about it in the comment section below!

Leaf mold of tomato

Quick facts

  • Leaf mold is not normally a problem in field-grown tomatoes in northern climates.
  • It can cause losses in tomatoes grown in greenhouses or high tunnels due to the higher humidity found in these environments.
  • Foliage is often the only part of the plant infected and will cause infected leaves to wither and die, indirectly affecting yield.
  • In severe cases, blossoms and fruit can also be infected, directly reducing yield.

Host and pathogen

Leaf mold is caused by the fungus Passalora fulva (previously called Fulvia fulva or Cladosporium fulvum). It is not known to be pathogenic on any plant other than tomato.

Identification

Signs and symptoms

Leaf mold symptoms on the upper leaf surface of tomato plant

  • The oldest leaves are infected first.
  • Pale greenish-yellow spots, usually less than 1/4 inch, with no definite margins, form on upper sides of leaves.
  • Olive-green to brown velvety mold forms on the lower leaf surface below leaf spots. Olive green to brown velvety sporulation on the lower leaf surface
  • Leaf spots grow together and turn brown. Leaves wither and die but often remain attached to the plant. Leaf death caused by severe leaf mold infection
  • Infected blossoms turn black and fall off.
  • Fruit infections start as a smooth black irregular area on the stem end of the fruit. As the disease progresses, the infected area becomes sunken, dry and leathery.

Environment

  • Optimal growth is at relative humidity greater than 85%.
  • Optimal temperature is between 71 °F and 75 °F, but disease can occur at temperatures as low as 50 °F and as high as 90 °F.

Biology and disease cycle

  • Spores of P. fulva can survive for 6 months to a year above ground at room temperature.
  • It is unknown if spores will survive on the surface of stakes, tools and high tunnel walls from one season to the next in Minnesota’s climate.
  • The pathogen forms dark, hard resting structures within infected plant debris.
    • These structures will produce an abundance of new spores when exposed to air. They are the most likely means for P. fulva to survive from one season to the next.
    • The leaf mold pathogen can survive on and in tomato seed and may be introduced to a new area by this route.
  • Spores of P. fulva can start an infection at a wide range of temperatures.
  • Relative humidity at or above 85 % will favor severe leaf mold epidemics.
    • Some disease can occur at humidity less than 85 %.
  • New spores form on the lower surface of infected leaves within 10 to 12 days.
    • If humidity remains over 85%, these spores will infect new leaves.
  • Within the growing season, multiple generations of the pathogen can be completed.
    • It can spread from leaf to leaf and plant to plant by wind, rain/overhead irrigation, tools, workers and perhaps insects.

Management

Resistant cultivars

  • Although varieties designated as resistant to leaf mold can be found in many seed catalogs, these may or may not be effective in reducing disease in Minnesota.
  • Resistant varieties should be used in combination with cultural control practices as part of an integrated disease management program.
  • There are currently 12 known races of P. fulva.
    • Each resistant cultivar protects against only one to a few races.
    • It is currently unknown which races of P. fulva exist in the United States of America. Therefore it is unknown which varieties will effectively reduce disease.
    • The population of P. fulva on a farm can change if new races emerge or are introduced from another area.
  • Growers with a history of leaf mold are encouraged to try resistant varieties on a small scale to determine their efficacy at the location.

Cultural control

  • Use drip irrigation and avoid watering foliage.
  • Space plants to provide good air movement between rows and individual plants.
  • Stake, string or prune to increase airflow in and around the plant.
    • Sterilize stakes, ties, trellises etc. with 10% household bleach or commercial sanitizer.
  • Circulate air in greenhouses or tunnels with vents and fans and by rolling up high tunnel sides to reduce humidity around plants.
    • Keep night temperatures in greenhouses higher than outside temperatures to avoid dew formation on the foliage.
  • Remove crop residue at the end of the season. Burn it or bury it away from tomato production areas.
  • Clean the high tunnel or greenhouse walls and benches at the end of the season with a commercial sanitizer.

Chemical control

Applications should be made prior to infection when environmental conditions favor disease to be the most effective. The first leaf mold infections of the season have been observed in the first week of June in Minnesota high tunnel tomatoes.

Fungicide applications should be repeated according to label instructions. It is important to alternate between different chemical families to avoid the development of pathogen resistance to particular active ingredients.

Below is a partial list of fungicides available for management of leaf mold on tomato.

Note: In Minnesota a high tunnel is considered a greenhouse for the sake of pesticide application. Read all label instructions carefully prior to use. If the product label prohibits use in a greenhouse, it cannot be legally applied in a high tunnel. If the product label provides specific instructions for use within a greenhouse or does not mention use in a greenhouse, it can be used in a high tunnel. Different formulations of the same product may vary on greenhouse use. The instructions on the label attached to the pesticide container must be followed.

Fungicide options for leaf mold control on tomato

Active ingredient Common product names Chemical family
Difenoconazole and Cyprodinil Inspire Super 3 and 9, respectively Good
Difenoconazole and Mandipropamid Revus Top 3 and 40, respectively Good
Cymoxanil and Famoxadone Tanos 27 and 11, respectively Good
Copper Kocide, Champ Formula 2, Nu-Cop 50DF M Fair
Mancozeb Dithane, Manzate, Penncozeb M Fair
Mancozeb and Zoxamide Gavel M and 22, respectively Fair
Azoxystrobin and Difenoconazole Quadris Top* 11 and 3, respectively

* While Quadris Top is often registered for greenhouse use, other Quadris formulations are not. Please ensure that the formulation of Quadris that you purchase is labeled for greenhouse use.

The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by the University of Minnesota Extension. A pesticide label is a legal document. Always follow the pesticide label directions attached to the pesticide container you are using. The site of use or plant to which the pesticide is to be applied must be listed on the label or the pesticide cannot be used. If a pesticide label prohibits use within a greenhouse, it cannot be used in a greenhouse or high tunnel in Minnesota. Remember, the label is the law.

Anna Johnson; Michelle Grabowski Extension educator and Angela Orshinsky, Extension plant pathologist

Reviewed in 2015

Tomato leaf mold in hoophouse tomatoes

Hoophouse tomatoes are one of the biggest moneymakers on small farms. While the hoophouse provides relief from many tomato diseases, some plant diseases are favored by the high relative humidity that can occur in hoophouses and greenhouses. Tomato leaf mold (Passalora fulva) is one of these diseases, and due to its biology, it can become a frustrating and recurring issue.

What is tomato leaf mold?

Tomato leaf mold is a fungal disease that can develop when there are extended periods of leaf wetness and the relative humidity is high (greater than 85 percent). Due to this moisture requirement, the disease is seen primarily in hoophouses and greenhouses. Tomato leaf mold can develop during early spring temperatures (50.9 degrees Fahrenheit) or those characteristic of summer (90 F). The optimal temperature tomato leaf mold is in the low 70s.

Symptoms of disease include yellow spots on the upper leaf surface. Discrete masses of olive-green spores can be seen on the underside of the affected leaves. The older leaves become infected first and die prematurely. The pathogen may spread rapidly during periods of prolonged relative humidity. The disease can cause flowers to drop but usually does not affect developing fruit. If infection occurs late in the season, yield losses will be minimal, but if the disease takes hold earlier, the premature defoliation will impact yield.

The pathogen survives by forming scleortia (familiar to those who have dealt white mold) that can survive in the hoophouse or greenhouse to infect future tomato plants when the conditions are right.

Tomato leaf mold causes yellow spots on the top of leaves (left), with corresponding olive sporulation underneath each yellow spot (right).

What can be done about tomato leaf mold?

Within the season

Limiting the relative humidity in the hoophouse can help to prevent this disease. Vent, if possible, to promote air movement. Increase plant spacing, remove weeds, and prune and trellis plants. Consider using drip irrigation to minimize leaf wetness. If watering overhead, irrigate in the morning so foliage can dry quickly.

There are organic preventive products available, which vary in price but performed similarly in Cornell University trials. Products trialed include Champ (Copper Hydroxide), Double Nickle (Bacillus amyloliquefaciens), Oxidate (Hydrogen dioxide), Regalia (Reynoutria sachalinensis extract) and Zonix (Rhamnolipid biosurfactant). While the treatments did reduce the amount of tomato leaf mold, the disease level was still high. In this trial, all treatments performed comparably, but when price is brought into consideration, the copper product Champ gave the best value. Note, only certain copper hydroxide formulations are approved for organic use, including Champ WG and Kocide 3000-O, and formulations with a higher percentage of active ingredient increase the Re-Entry Interval (REI) to 48 hours. Copper products with a lower percentage of active ingredient will lower the REI, but do not work as well against this disease. For more information on product trials, see “Managing Leaf Mold in High Tunnel Production.”

Conventional fungicides available for treating this disease include mancozeb formulations, Revus Top (mandipropamid + difenoconazole) and Tanos (cymoxanil + famoxadone). See the table below for more information on rates and greenhouse use for the products from the Cornell study, and conventional fungicides

Fungicides for leaf mold of tomatoes – Passalora fungus

Product (*= OMRI label)

FRAC Mode of action

Rate

PHI/REI

Greenhouse Use?

Kocide*, Champ*, others
copper hydroxide

M1

Various rates depending on formulation.

0 day/48 hours or see label depending on formulation.

Check label, most are silent or yes

Manzate, Koverall, others
mancozeb

M3

Various rates depending on formulation.

7 days/24 hours or see label depending on formulation.

Silent or yes

Tanos
famoxadone +
cymoxanil

7 + 9

8.0 – 10.0 fl. oz. per acre

3 days/12 hours

Silent

Revus Top
mandipropamid +
difenoconazole

40 + 3

5.5 – 7.0 fl. oz. per acre

1 day/12 hours

Silent

Double Nickel LC*
Bacillus amyloliquefaciens

0.5 – 6 qt. per acre

0 day/4 hours

Silent

Oxidate*
hydrogen dioxide + peroxyacetic acid

NC + NC

32 fl. oz. – 2.5 gal. per 100 gal. water depending on severity

0-day/1 hour

Yes, do not apply high rate to flowering crop

Regalia*
Reynoutria sachalinensis

P5

1.0 – 4.0 qt. per acre

0 day/4 hours

Silent

Zonix*
rhamnolipid biosurfactant

NC

45 – 76 fl. oz. per 100 gal of water

Silent/4 hours

Yes

Pale yellow lesions on the upper side of greenhouse tomato leaves. Photo by Rebecca A. Melanson, Mississippi State University Extension, Bugwood.org.

Destroying crop residue is also important to reduce the number of sclerotia in the hoophouse. Sanitizing the interior of the house as well as any stakes and tools that contacted the plants will reduce the inoculum load next year.

Long-term

If this is a perennial issue in your hoophouse, choosing resistant varieties will be a cornerstone of management. Cornell has developed a list of cherry and slicer type tomatoes that have performed well in New York. For an overview of tomato leaf mold and the varieties recommended in New York, see “Leaf Mold in High Tunnel Tomatoes.” Note that tomato leaf mold has many strains, and it isn’t known how the varieties recommended in New York would respond to Michigan strains of tomato leaf mold.

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