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Botrytis Likely to Appear

May 29, 2002

If there were a fungus that thrived in cool, wet conditions, we would certainly expect to see it in Illinois now. Botrytis fits the bill perfectly and will likely show its characteristic gray mold appearance soon. The fungus is widespread, especially on dead plant material in cool, wet conditions. Weak or wounded material is also susceptible to infection.

We have all sorts of molds and mildews that cause infectious disease on plants, often causing confusion to growers trying to establish a disease-management plan. Botrytis blight is one of the fungal diseases that causes a rather distinct type of sporulation. The Botrytis fungus forms gray masses of spores on the infected plant part. The spore mass is often very fluffy and dusty. Color may range from green to brown but always appears dusty because of the mass of spores produced by the fungus, so gray mold is an appropriate common name for the disease.

We have seen gray mold on garden flowers, but this fungus has a broad host range, including herbaceous ornamental plants, vegetables, fruits, and green-house crops. Infection may occur on buds, flowers, foliage, stems, bulbs, and even roots. You will see sporulation on the most tender, newest growth, as well as on the tissues that are injured or dying. Botrytis may be found on the new buds and dying flowers on the same plant. Refer to Report on Plant Disease (RPD) no. 623 (available in Extension offices or on the University of Illinois Extension Vista Web site) for a list of plants commonly infected by this fungus. Some of the more common hosts we see infected with gray mold are zinnia, peony, marigold, phlox, rose, snapdragon, strawberry, tulip, and geranium.

To manage the disease, we need to produce conditions that do not favor fungal development. Clean up plant debris and remove dead or injured plant material. Crowded plants, rain, or overhead watering that splashes spores from plant to plant will increase chances of infection. Keep fruit (strawberries) from touching bare soil. Follow seed-packet recommendations for plant spacing to allow good air movement in the garden. Avoid overfertilization and constantly wet mulches. Know how to identify this disease so that you can stop it quickly. Fungicides are effective against Botrytis but only as protectants. Because the fungus can increase on injured tissue (late frost), you might want to consider protecting nearby new growth and flowers. Fungicide recommendations can be found in the Illinois Home, Yard, and Garden Pest Guide or the Commercial Landscape & Turfgrass Pest Management Handbook.

Author: Nancy Pataky


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