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.

Cornell University

Leaf mold occurs sporadically on Long Island, and elsewhere in the USA. This disease develops under humid conditions. Therefore it is more common in gardens and in protected environments (greenhouses and high tunnels) than in commercial production fields, where better air movement reduces humidity.

The fungal pathogen needs high humidity (at least 85% RH) in order to be able to infect. In can infect when the leaf surface is wet. Leaf mold can develop over a wide temperature range (39 – 90 F). Optimal temperature is 72 – 75 F.

Symptoms mostly develop on leaves, appearing first on older leaves. Color of leaf mold spots on upper leaf surfaces progresses from pale green to yellow. Spots are not distinct as they lack a clearly defined border, in contrast with most other foliar diseases. Thus affected leaves may look like they have a general yellowing due to a nutrient deficiency.

Spores form on the lower surface of leaves below the yellow spots. Initially they appear greenish brown, becoming darker brown with age and developing a velvety appearance. Severely affected leaves die prematurely.

Symptoms sometimes also occur on stems, petioles, blossoms and fruits. Infection can kill blossoms. A black, leathery rot can develop on the stem end of green and ripe fruit.

An important initial source of the fungus causing leaf mold is spores from other infected plants, including susceptible weeds in the nightshade family. The spores are easily moved by wind and splashing water. This pathogen can be seed-borne. Leaf mold can reoccur when tomatoes are planted again in the same location because the pathogen can survive in soil at least one year as spores or in infested plant tissue from the previous planting.

Management practices for leaf mold include managing humidity, changing the location where tomatoes are grown, selecting resistant or less susceptible varieties, applying fungicides, and removing tomato plant debris after last harvest or incorporating it deeply into the soil.

Managing humidity is an especially important practice for this disease. Improve air movement around plants by planting with good spacing between plants, locating rows parallel to the prevalent wind direction in an open area, staking or trellising plants, and pruning excess branches and dead leaves. Provide water to the base of plants rather than using sprinklers that wet leaves.

Growing tomatoes in full sun will facilitate drying of leaves after rain. Avoid excessive amounts of nitrogen fertilizer. Resistance has been bred into a few varieties adapted to the protected environment of greenhouses and high tunnels. Resistant varieties can vary in susceptibility to leaf mold because the resistance is not effective for all 12 known races of the pathogen.

Two images below: Symptoms of leaf mold on nightshade, a weed related to tomato.

Tomato Leaf Mold

Tomato leaf mold is a common fungus that attacks tomatoes grown in humid places. The mold attaches itself to the leaf and feeds off of the humidity to grow and thrive.

It is vital to take care of the situation immediately so that the foliage isn’t dramatically infected. Infected leaves will decrease the amount of tomatoes yielded.

Luckily, this fungus is pretty simple to treat and cure.

Causes and Symptoms

With this type of fungus, it is rare that the fruit is infected as well. The signs to look for are all on the leaves. The tops will begin to develop small, white, gray, yellow, or pale green patches. The underside of the leave will have a fuzzy feel that is purple in color. Sometimes the fuzz will be olive green. The “fuzz” is actually spores of the fungus.

The infected tissue becomes yellowish-brown and the leaf begins to wither, eventually falling off of the plant. Untimately the whole plant will wither and die.

In the rare case that the blossom or fruit is infected, the mold will appear as a black sore-like lesion. The black can grow to cover over half of the surface area of the plant or blossom. Tomato leaf mold affects ripe tomatoes as well as green tomatoes.

Treatments and Control

When you notice the infected areas, the first thing you can do is let the plants air out. If they are being grown in a green house, air exposure is a must, because the humidity that the fungus needs to survive is dried up.

If the tomatoes are being grown outside, try to keep from wetting the leaves when you are watering the plants. When you water the plants, earlier watering is optimal because it allows the plant time to dry when the sun comes, keeping humidity around leaves to a minimum.

Another option for treatment is fungacide sprays. When using these sprays, be sure to cover each part of the plant that is above ground, paying special attention to the underside of the leaf. Some of the most widely recommended sprays are those containing calcium chloride. There are some organic fungicides available as well.

Some remedies that can be mixed up right in your kitchen include an apple-cider and vinegar mix to treat the mold. Corn and garlic spray can be used to prevent the fungi outbreaks before they even occur. A milk spray is also a natural, helpful cure.

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.

Tomato Mold

Photo Credit: Rudi Riet. All rights reserved.

The battles fought in the invisible war between pathogens and the cells they attack can be as complex as wars between nations. Armies of microbes produce powerful and insidious chemical weapons, and in response, plant and animal cells come up with ingenious methods of defense. In this Science Update, you’ll hear about a researcher who’s helping tomato plants fight back against a particularly diabolical foe.

Transcript

Why good tomatoes turn bad. I’m Bob Hirshon and this is science update.

Anyone who’s raised tomatoes knows the depressing symptoms of black mold. Plant pathologist David Gilchrist at the University of California at Davis describes them.

Gilchrist:
It’s a very sad moment, when the tomato that is ripening, is just about to be picked and all of a sudden the fruit begins to show little black spots, and pretty soon, the fruit is something that you wouldn’t want to take into your kitchen.

Gilchrist says the mold does its dirty work by tricking the tomato’s cells into committing suicide. He explains that inside every living cell are proteins that let the cell kill itself when it’s no longer useful. The black mold fungus produces chemicals that trick the tomato cells into activating these suicide proteins.

Gilchrist:
And it’s that death, then, that provides a mechanism for acquiring a food source, which the pathogen can then use to spread in the tissue.

There are genes found in many plants and animals that stop this programmed cell death. Gilchrist and his colleagues have been able to insert these genes into tomato plants and make them resistant to the black mold.

He says the research holds promise for the treatment of many other diseases as well, since many pathogens use the same trick to attack living cells.

For the American Association for the Advancement of Science, I’m Bob Hirshon.

Making Sense of the Research

It may seem strange, but the ability to die on command is one of the most important features of living cells. In fact, no plant or animal could grow, develop, or even survive without it. Every single cell in your body has a genetic program built into it that will cause the cell to self-destruct if the program gets switched on. This pre-programmed self-destruction – a kind of cellular suicide – is called apoptosis.

Apoptosis plays a key role in several processes. One of them is general housekeeping: when cells get old or damaged, they need to be cleared out to make way for new ones. Sometimes it’s a part of development: for example, the reason we don’t have webbed fingers and toes is because the cells in between them are programmed to die off while we’re still in the womb. And other times, it’s a form of self-defense: if a toxic chemical or a virus gets into a cell, the cell will destroy itself rather than create a safe haven for the invader to grow and spread.

When the attack is small in scale, this can save the organism’s life. But if too many cells are affected, the organism can suffer severe damage. That’s what happens when tomatoes get black mold: a chemical from the mold triggers apoptosis in the tomato cells, killing them off in large numbers. By the time you pick the fruit, the entire tomato just collapses. Gilchrist and his colleagues have genetically engineered the tomatoes so that they don’t respond to that particular chemical. As a result, the apoptosis never happens, and the tomato stays healthy and edible.

Scientists would like to apply this kind of knowledge to human diseases, including Alzheimer’s disease and AIDS, which trick cells into self-destructing prematurely. You might think they would try to stop apoptosis in all our cells all the time, but that would be deadly. In fact, the exact reason why cancer cells are so dangerous is because they won’t die; instead, they grow and multiply like weeds and take over the body. Some researchers are actually trying to treat cancer by triggering apoptosis in the renegade tumor cells.

Now try and answer these questions:

  1. What is apoptosis? What are some reasons why it’s important?
  2. How does apoptosis figure into the black mold disease in tomatoes?
  3. What would happen if all of your cells lost the ability to self-destruct?
  4. Can you think of other examples of things in which certain parts might self-destruct, shut off, or disappear for the good of the whole? Think broadly: it could be a group, an organization, a machine, a society, or any other system.
  5. Apoptosis is important in development because it helps shape certain parts of your body, like your fingers. Can you think of other examples of things that are created by taking parts of it away, rather than just building it up? Again, be as broad as you like.

For Educators

Read more about Dr. Gilchrist’s work with tomatoes and apoptosis at Dateline UC Davis.

See pictures of apoptosis at Cells Alive.

The article, Researcher instigates cancer cell suicide, discusses how a Wayne State University School of Medicine physician-researcher has developed a personalized therapy to treat a wide range of cancers. The treatment is based on a naturally occurring human enzyme that has been genetically modified to fool cancer cells into killing themselves.

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Gray mold of tomatoes

Quick facts

  • Gray mold thrives in the high humidity found in high tunnel tomato production.
  • Gray mold is rare in Minnesota field grown tomatoes.
  • The fungal pathogen infects all above ground plant parts.
  • It can be highly destructive when environmental conditions favor disease.

Pathogen

The fungus Botrytis cinerea.

Host range

More than 200 plant genera, primarily broad leafed plants.

Identification

Signs and symptoms

Gray mold infection on a tomato leaf

  • Leaves have irregular to V-shaped brown blotches, often starting at the margin of the leaf.
  • Die-back symptoms appear as infection progresses from leaves, through petioles, towards the main stem.
  • Brown, oval lesions can girdle the stem. Gray mold infection on tomato stems
  • Infected fruit develop a pale, soft, watery rot.
  • Fruit symptoms occur on green and red fruit; while on the plant and post-harvest.
  • Failed fruit infection results in white rings or halos on the fruit, called ghost spots. Small white rings on tomato fruit indicate failed gray mold infections
  • Infected flowers turn brown and die.
  • In high humidity, fluffy gray spores cover infected plant parts.
    • The spores are light brown-gray on black stalks.

Environment

  • Cool temperatures of 60-75°F (60-70°F optimum)
  • Temperatures greater than 82°F suppress fungal growth and sporulation.
  • High humidity (greater than 80%)
  • Spore germination is optimal with leaf wetness of 5 to 8 hours.

Biology and disease cycle

  • The fungus survives on numerous weed hosts, as a saprophyte on dead plant material, and as hard resting structures (sclerotia) in plant debris and soil.
  • Spores are spread short and long distances by wind and rain, equipment and workers.
  • Infections begin on weak, dying or wounded plant tissue.

Management

Open all | Close all Plus sign (+) if content is closed, ‘X’ if content is open. Resistant varieties

There are no tomato varieties with resistance to gray mold.

Plus sign (+) if content is closed, ‘X’ if content is open. Cultural control

  • Fluffy gray spores of Botrytis cinerea, the gray mold pathogen Keep humidity and leaf wetness low by rolling up high tunnel sides, increasing ventilation and avoiding overhead irrigation.
  • Space plants well to avoid excess humidity in dense plant canopies.
  • Remove infected stems, leaves and fruit. Place in a plastic bag.
  • Clean up leaf debris on the ground.
  • Prune plants in the afternoon when the morning dew has dried.
  • Maintain consistent and adequate soil moisture to promote healthy plants and fruit.
  • Remove all plant debris at the end of the season.

Plus sign (+) if content is closed, ‘X’ if content is open. Chemical control

  • Fungicides are available for control of gray mold on tomato.
    • They should only be used once cultural practices have been implemented.
    • Apply fungicide according to label instructions.
  • Fungicide-resistant gray mold has been reported on many crops.
    • Rotate fungicide groups and/or tank mix fungicides to avoid producing fungicide-resistant isolates.
  • For a current list of fungicides for gray mold management see the Midwest Vegetable Production Guide.

Angela Orshinsky, Extension plant pathologist and Michelle Grabowski, Extension educator

Reviewed in 2016

Tomato Leaves Turn White: How To Treat Tomato Plants With White Leaves

One of the most commonly grown garden plants, tomatoes are quite sensitive to both cold and too much sun. Because of their extremely long growing season, many people start their plants indoors and then transplant later in the growing season once the soil has consistently warmed. The transplantation of the tomato seedlings is where one may run into a problem. Their susceptibility to temperature and light extremes often renders them vulnerable to white tomato leaves. Let’s explore this white leaf color on tomato plants.

Why Do Tomato Leaves Turn White?

If you’re unlucky enough to find a silver or white leaf color on your tomato plants, it is undoubtedly the result of either sun damage, cold vulnerability or some sort of disease (most likely fungal).

The most common cause of leaves turning white in tomatoes, especially young seedlings that are recently transplanted, is exposure to intense sunlight. Although tomato plants need full sun for healthy growth, a sudden change of venue from indoors to outdoors may shock the plants and cause the tomato leaves to turn white. Generally, the damage from sunlight appears as a border of white leaf color on the tomato plant. The leaves may curl and break, leaving minimal foliage on the plant. Winds in the area of transplantation exacerbate this condition as well. Mature tomato plants suffering from sunscald will include blistered or papery fruits.

The solution to tomato plants with white leaves due to sun over exposure is simple in retrospect. In the future, allow the transplants to languish in the shade for a few days and/or move them outside on a cloudy day, then gradually place them in the sun for a couple of hours each day over the course of one or two weeks. This is called hardening off. Either of these gives the plant time to acclimate to its more radical environs.

If hot, dry winds are an additional issue, try placing a windbreak around the transplants or relocate to a protected area. With either issue, if the windburn or sun scorch is not severe, the plant will likely recover; remove any afflicted leaves to discourage disease.

Fungal Reasons for Tomato Plants with White Leaves

Other than environmental exposure, another explanation for tomato plants with white leaves is disease. Primarily the disease is fungal in variety and resulting from the same cause, overwatering. Too much water in the soil stimulates the fungal spores and causes root rot, Alternaria or Septoria leaf spot, which has dark borders surrounding the white blotches on the leaves.

Transplants should be watered deeply for the first three days and thereafter, dependent on your climate, once a week to every two weeks. This promotes deep root development and deters fungal spores from taking hold. If a fungal disease has taken root, so to speak, try a fungicide made for use on tomato plants to repair any leaves that are turning white on your tomatoes.

Nutrients Causing Leaves Turning White in Tomatoes

Lastly, a potential cause of the leaves turning white in your tomatoes is a lack or surplus of nutrients. Plants lacking nitrogen or phosphorus may show whitening or yellowing of their leaves. A tomato fertilizer containing the proper amounts of these nutrients is a likely solution.

Additionally, deficiencies of calcium or magnesium will also cause whitening of leaves with the leaf veins retaining their green hue. Again, an application of the proper fertilizer is in order. Additionally, garden lime will aid in the calcium deficiency.

Leaf mold of tomato

  • 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.

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.
  • 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.
  • 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.

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

Passalora fulva

Leaf mold caused by Passalora fulva (previously Fulvia fulva) is primarily a disease of greenhouse-grown tomatoes and is most serious in plastic greenhouses where the relative humidity is high. The pathogen is found worldwide and is occasionally a problem on field grown tomatoes.

Identification:

Foliage is usually the only tissue affected. Symptoms begin as pale green or yellowish spots without well defined margins on the upper leaf surface which turn a distinctive yellow. Lesions coalesce when disease is severe and the foliage dies. An olive, green mold on the lower leaf surface is visible. Infected foliage curls and withers and may drop from the plant. Blossoms, stems, and fruit are occasionally attacked and blossoms may be killed. Fruit symptoms consist of a dark, leathery rot at the stem ends.

Life Cycle:

P. fulva survives as an saprophyte on infected plant debris, as conidia, or as sclerotia in the soil. Seed can be contaminated and serve as the initial source of disease. Conidia, which are readily spread by rain and wind, can survive up to one year. Conidia may also be spread on tools, workers’ clothing, and insects. The pathogen is dependent on high relative humidityand high temperatures. Leaf mold does not occur where relative humidity is less than 85%.

Cultural Controls & Prevention:

  • Crop residue should be removed and destroyed after harvest.
  • Start with certified, disease-free seed or treat seed with hot water.
  • Sanitize greenhouse thoroughly in between crop cycles.
  • Minimize long periods of leaf wetness by avoiding wetting the foliage and the use of fans to circulate air.
  • Staking and pruning to increase ventilation reduces disease spread.
  • Maintain night temperatures in the greenhouse higher than outside temperatures.
  • Fungicides effectively control this disease.

Chemical Controls & Pesticides:

For current information on disease recommendations ins specific crops including information on chemical control & pesticide management, please visit the New England Vegetable Management Guide website.

Crops that are affected by this disease:

  • Tomato, Field
  • Tomato, Greenhouse

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