Tomato Diseases: How To Fight Leaf Mold

by Matt Gibson

About Leaf Mold

Leaf mold is a common fungal disease that affects tomatoes that are cultivated in especially humid environments. Feeding off of the humidity, the mold grows and thrives after attaching itself to the leaves of the tomato plant. Once the mold is noticed, immediate action is required to save the plant, otherwise the foliage will be compromised, which will reduce the amount of tomatoes your plants will yield. Fortunately for tomato growers, this fungal disease is relatively easy to treat and cure.

Causes And Symptoms of Leaf Mold

The first signs of leaf mold are, as you might expect, on the leaves themselves, as the topside of the leaves start to develop small gray, yellow, white, or pale green patches. The underside of the leaves begin to develop a fuzzy texture and turn purple. Oftentimes, the fuzz will appear in an olive green color. The fuzzy texture is actually the spores of the mold fungus. The fruit of the tomato plant is rarely infected by leaf mold.

As the disease progresses, the infected tissue of the leaves become yellowish-brown and the leaf starts to wither, eventually falling off of the plant altogether. If not treated, the plant will eventually wither and die.

Though the fruit and blossoms of the tomato plant are rarely affected by leaf mold, it does occur occasionally. When the fruit or flower is infected, it appears as a black legion on the surface of the fruit or bloom. The black part grows and spreads out, eventually covering over half of the surface area of the flowerhead or fruit. Tomato leaf mold can affect both ripe tomatoes and immature green tomatoes.

Treatment and Control of Leaf Mold

Upon noticing the infected areas, the first step is to let the plants air out and dry. If they are being cultivated in a greenhouse, expose them to dry air conditions, because the humidity that the fungus needs to survive and thrive is dried up in the open air.

If the tomatoes are being cultivated outdoors, try to keep the leaves dry when watering the plants. One thing you can do to help keep the leaves as dry as possible is to water in the early morning hours, that way the plant has plenty of time to dry before the sun comes out, which will keep the humidity around the leaves low. You can also try drip irrigation methods, or soak watering methods to attempt to water the soil without ever wetting the leaves of the plant.

Another treatment option is fungicidal sprays. When using fungicide sprays, be sure to thoroughly cover all parts of the plant that is above ground, focusing specifically on the underside of leaves. Calcium chloride sprays are among the most highly recommended types for leaf mold. There are a few organic fungicides on the market as well.

There are also a handful of natural remedy recipes that you can try that are made out of common household items that can be mixed up in your kitchen and sprayed directly on your tomato crops. An apple-cider and vinegar mix is believed to treat the mold effectively. Corn and garlic spray can also be used to prevent fungi outbreaks before they even occur. There is also a milk-based spray that is touted as an all-natural, helpful cure for leaf mold.

Commonly Asked Questions Leaf Mold

How do you get rid of leaf mold on tomato plants?

The initial source of the disease is often infected seed, but it can be spread by a variety of factors, including rain, wind, on tools, on clothing, or via insect activity. High humidity and warm temperatures encourages the spread of the disease.

Once you notice the symptoms of leaf mold on your tomato plants, there are plenty of ways to treat the disease. The first step is to allow the plants to dry out completely. If you are growing them in a greenhouse, it’s a good idea to expose them to dry air conditions as soon as you notice the presence of leaf mold.

If cultivating outdoors, try to keep the leaves as dry as possible during the watering process. If possible, water them early in the morning, so that the plants have plenty of time to dry out before the sun comes out. Alternatively, abandon overhead watering techniques for a drip irrigation system or soaker system, both of which water the soil directly and do not get the leaves of the plant wet in the process.

Another treatment option is fungicidal sprays. When treating tomato plants with fungicide, be sure to cover all areas of the plant that are above the soil, especially the underside of leaves, where the disease often forms. Calcium chloride-based sprays are recommended for treating leaf mold issues. Organic fungicide options are also available.

There are also a handful of recipes available for natural remedies that you can mix together in your kitchen. These contain common household items, such as apple cider vinegar, corn, garlic, and milk, which you might already have on hand in your kitchen. We recommend fungicidal sprays over home remedies but some gardeners have had success with homemade concoctions.

How do you kill leaf mold?

Plant resistant cultivars and practice cultural control methods to keep leaf mold from attacking your tomatoes. It is currently unknown which races of P. fulva exist in the United States, and each cultivar is only resistant to one or a few races, so try resistant varieties on a small scale to determine their strength at a given location.

Other ways to prevent leaf mold include cultural control practices such as drip irrigation and proper spacing, and chemical control methods such as organic and chemical fungicides.

Want to learn more about tomato leaf mold?

University of Minnesota Extension covers Leaf Mold of Tomato

Gardeners’ World covers Tomato Leaf Mold

Gardening Know How covers Managing Tomato Leaf Mold

plantix covers Leaf Mold of Tomato

Royal Horticultural Society covers Tomato Leaf Mould