Phytophthora blight of peppers can attack the roots, stems, leaves, and fruit, depending upon which stage plants are infected. A grower not knowing what to expect might first encounter the disease at mid-season when sudden wilting and death occur as plants reach the fruiting stage (fig. 1). Early infected plants are quickly killed (foreground, fig. 1), while later-infected plants show irreversible wilt (fig. 2). Often a number of plants in a row or in a roughly circular pattern will show these symptoms at the same time.
Fungus-infected seedlings will damp off at the soil line, but relatively few plants die when temperatures are cool. Far more commonly, the disease will strike older plants which then exhibit early wilting. Stem lesions can occur at the soil line and at any level on the stem. Stems discolor internally, collapse, and may become woody in time (fig. 3). Lesions may girdle the stem, leading to wilt above the lesion, or plants may wilt and die because the fungus has invaded the top branches before the stem lesions are severe enough to cause collapse.
Leaves first show small dark green spots that enlarge and become bleached, as though scalded (fig. 4). If the plant stems are infected, an irreversible wilt of the foliage occurs.
Infected fruits initially develop dark, water-soaked patches that become coated with white mold and spores of the fungus (fig. 4). Fruits wither but remain attached to the plant (fig. 1). Seeds will be shriveled and infested by the fungus.
Because of the wide host range and the various phases at which plants can be infected, refer to the table for clarification of the crops affected and the Phytophthora species involved.
The symptoms of buckeye rot of tomato (mainly caused by P. parasitica, fig. 5) consist of leathery tan or brown spots, often appearing as concentric rings or bands on green fruit. Lesions can appear on the shoulder or, more commonly, on the blossom end where the tomato has contact with wet soil. On butternut squash (fig. 6) (and on several of the other crops listed with fruit symptoms) tan or brown lesions may give a banding affect or appear as large circular spots. Under humid conditions, white cottony mycelium and spores occur on the surface, and fruit are likely to rot quickly from secondary organisms.