Tomato Diseases: Buckeye Rot (Phytophthora Root and Crown Rot)
Phytophthora parasitica, P. capsici. Brown spots appear on green and ripe fruit, often at the blossom end. The spots have bands of dark and light brown rings. These spots remain firm and smooth, although internally the rotted tissue turns mushy and can cover half the fruit. Young green fruit, when infected, usually become mummified. A white cottony fungal growth appears under moist conditions. Fruit touching or near the soil are most likely to become infected.
Phytophthora can cause a root and crown rot of tomato plants at all ages. Damping-off symptoms occur on seedlings while infections of the roots and crowns of young plants cause rapid wilt. On established plants, brown water-soaked lesions appear on roots, extending into the lower part of the stem. Severely affected roots become necrotic and decayed. The leaves become bronze and later dieback from the tip.
On stems, the canker that develops is pale green to brown and may extend more than 15 cm. A fine weft of fungal growth may be evident under wet conditions. The canker girdles the stem and causes wilting and death.
Foliage is not directly affected by P. parastica, but P. capsici can cause a blight of foliage and defoliate the plant during extended rainy weather and warm temperatures, followed by complete plant collapse.