The Purdue Plant and Pest Diagnostic Laboratory

P&PDL Picture of the Week for
March 3, 2014

Growing Tomatoes in the Greenhouse and Botrytis Gray Mold

Dan Egel, Vegetable Pathologist, SWPAC, Botany & Plant Pathology, Purdue University

There are two photographs that accompany this week's message. The first photo is of a disease known as Botrytis gray mold of tomato. The second is of a greenhouse where tomatoes are being grown. In just a few words, I will try to explain the connection between these photos.

Botrytis gray mold is a disease that can affect many plants including tomato. Gray mold thrives in the humid atmosphere of a greenhouse. The fungus that causes gray mold also survives in crop residue in the soil. Therefore, any management strategy that reduces crop residue (small bits of leaves, stems and fruit) in the soil will help to reduce the severity of gray mold. The best way to reduce crop residue in the soil is to practice crop rotation. After growing tomatoes, do not grow any crop in the tomato family for 3-4 years.

Unfortunately, most greenhouse tomato growers find crop rotation impractical, preferring to grow tomatoes year after year. My recommendation to such growers is to remove the tomato plants after the season is complete. Plus, I recommend using a ground cover to reduce the amount of crop reside that enters the soil.

The second photograph shows the white woven ground cover that we use in our greenhouses at the Southwest Purdue Agricultural Center in Vincennes to reduce the amount of crop residue incorporated into the soil.  Below the white ground cover, we use a black landscape cloth. The ground cover can be used multiple years if cleaned properly. The black landscape cloth is used one year and discarded.

There are many other tomato diseases caused by microbes that survive in crop residue. Tomato growers should make every effort to reduce the amount of crop residue that enters the soil.

Click image to enlarge

Figure 1. Botrytis gray mold of tomato. The fungus that causes this disease may survive in crop residue to infect tomato plants the following year

Figure2. The white woven ground cover between the rows of tomato plants helps to reduce tomato crop residue (including infected leaves) that might become incorporated into the soil and possibly cause disease the following year. The lower leaves of the tomato plants exhibit a leaf curl which is normal for older leaves.

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service