From the Ground Up: Summer Mold and Fungus Problems on Plants

mold and fungus

By ISU Extension and Outreach Linn County Master Gardener Judy Stevens

With summer activities in full swing it is easy to ignore the garden and hope everything is doing ok without your constant surveillance.  However, the excess moisture can create problems in the form of plant diseases.

The most common high moisture problem is mildew, and mold fungus. One of the varieties is tomato blight. Tomato blight is caused by a fungus that lives in the soil around the tomato plant and is carried to the lower leaves of the tomato when the rain splashes to the lower leaves of the plant resulting in black spots, and yellow leaf. The blight will spread up the leaves of the entire plant if not controlled.

There is no cure for the tomato blight, it can only be controlled. One of the first preventive measures to implement is mulch. Mulching around the base of the plant will help to keep the spores in the soil and not on your tomato leaves.

Do not water plants when the foliage is wet. Water only at the base of the plant, in the morning if possible to minimize the time the foliage is wet.

If you remove the infected leaves do so carefully. Wash your hands after removing the leaves and before touching the healthy part of the plant so you do not spread the fungal spores. The application of a fungicide may help to control the fungus but will not completely eradicate it. Follow the directions on the product label.

In planning for the next years garden in blight prevention rotate your tomato location, clean up all the tomato debris yet this fall and look for blight resistant plant varieties.

Lilacs, Peonies, Monardia, and Zinnas, may develop a white powdery coating on their leaves. This is called powdery mildew. Although this is unsightly it usually does not kill the plant. The best prevention is to plant these plants in sunny locations and thin the plants regularly to allow good air circulation. In the spring select mildew resistant plants.

You may also discover horn shaped orange mushrooms in your mulch (like the one in the photo at the top of the page). These are called stinkhorns which attract flies and bugs. Destroy the stinkhorn with a rack or hoe to prevent the flies from spreading the spores. No other treatment is necessary.

Large toadstools can also appear in your lawn. These are the result of heat and moisture and organic matter, often times it's old tree roots. The toadstools are harmless and will dry up and wither or become a victim of your lawnmower.

All said the weather conditions are very conducive to all kinds of molds, mildews, and fungi.

There are thousands of species of fungi but to find more information about the particular species you are plagued with contact the Linn County Master Gardener Hotline at (319) 477-0647.   


Photo via ISU Horticulture and Home Pest News

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