Do your tomatoes have large brownish spots with concentric rings that resemble a buckeye? Are these spots near the blossom end or where they contact the soil? If so, then your plants may have buckeye rot of tomato, a fruit rotting disease caused by a soil borne fungus.
What is Tomato Buckeye Rot?
Buckeye rot on tomatoes is caused by three species of Phytophthora: P. capsici, P. drechsleri and P. nicotiana var. parasitica. Phytophthora species vary by tomato-producing region. Tomatoes with buckeye rot most commonly occur in the southeast and south central regions of the United States.
Tomato buckeye rot typically follows prolonged warm, wet conditions and the disease is important wherever there is high humidity and abundant soil moisture. The disease induces fruit rot of tomato, pepper and eggplant.
The fungus is introduced through infected seeds or transplants, or from volunteer plants or the previous crop. It attacks both green and ripe fruit and can spread by surface water and splashing rains. Fungal spores are produced when the soil is wet and above 65°F. (18 C.). Temperatures between 75 and 86°F. (24-30 C.) are ideal for disease development.
Tomato buckeye rot begins as a small brownish, water-soaked spot that usually appears at the point of contact between fruit and soil. At first, it is firm and smooth. The spot increases in size and develops the characteristic alternating rings of light and brown bands. The lesions become rough and sunken at the margins and may produce a white, cottony fungal growth.
Treating Buckeye Rot on Tomatoes
Let’s look at a few strategies to preventing and controlling the symptoms of buckeye rot on tomatoes.
Ensure proper soil drainage. If you have clay soil, amend with organic matter. Soil that does not drain properly between waterings is more vulnerable to fungal infections.
Avoid soil compaction and disinfect heavily infested soils with a soil fumigation. Planting in raised beds is a good way to help avoid either of these issues.
Crop rotation, changing the location in your garden where tomatoes are grown, is another good idea.
Apply fungicides that contain chlorothalonil, maneb, mancozeb, or metalaxyl as their active ingredient on a regularly scheduled spray program. (Follow the manufacturer’s label directions and restrictions.)