Buckeye Rot of tomato is caused by three species of the soil borne fungus-like water mold, Phytophthora: P. capsici, P. drechsleri, and P. nicotiana var. parasitica. The disease is common in areas with high rain fall and humidity such as in the southeastern and south central US. It usually appears when the temperatures are between 75 and 85 F and the soil is wet, causing damage to both the stems and fruit of eggplants, peppers, potato, pineapple and tobacco as well as tomatoes. Green or ripe fruits that touch the ground are particularly susceptible and develop brown, wet-looking spots that increases in size and develop alternating light and dark brown concentric rings as it grows larger. The spot start out smooth and firm but may become soft and produce a cottony white mass. Splashing water as well as surface water can spread the disease from plant to plant. Photo Credit CALS
- Avoid compacted, heavy, poorly drained soils and low areas; plant in raised beds if necessary.
- Remove infected plants immediately and dispose of them to reduce the spread of the fungus. Wash tools, hands, and clothing that may carry the disease.
- Remove and dispose of crop residual at the beginning or end of the growing season.
- Use a 3 year crop rotation scheme with crops from other plant families
- Water less frequently but deeply and in the morning using drip irrigation to reduce splash, but don’t over-water.
- Stake or mulch plants to keep the fruit off the ground and reduce the effects of rain splashing spores onto plant
- Increase air circulation by increasing space between plants or trimming excess foliage
- Spray with a solution of 1 tablespoon baking soda, 2 1/2 tablespoons vegetable oil, and 1 teaspoon of liquid soap (not detergent) per gal of water. Repeat every 2 weeks, more often if rain washes the solution away.
- Spray with a prepared solution of Bacillus subtilis about every 2 weeks or when rain has washed it off the leaves.
- For very severe infestations spray with copper or sulfur, heeding cautionary warnings on the containers. These are more demanding solutions to the problem and the copper application will require special equipment.