How to Manage Pests
UC Pest Management Guidelines
Pathogens: Phytophthora root rot: Phytophthora capsici, P. nicotinae var. parasitica
Aboveground symptoms of root rot include rapid wilting and death of affected eggplant plants. Close examination of the roots and stems of affected plants is necessary to confirm the cause of disease. The disease can develop at any stage of eggplant plant growth. Tap roots and smaller lateral roots show watersoaked, very dark brown discoloration of cortical and xylem tissue. Very few lateral roots remain on diseased plants and the taproots may also be shorter compared to those of healthy plants. The most striking difference between healthy and diseased plants is the total amount of root tissue. Stems are usually infected at the soil line. Stem lesions are first dark green and watersoaked, then dry and turn brown. The lesions may girdle the stem and result in wilting of plants above the lesions and subsequent death.
The fungi produce thick-walled oospores that can survive prolonged periods of adverse conditions. Transplants or soilborne inoculum are sources of primary infections. Irrigation water often disseminates fungal propagules from infested areas to other parts of the field. Thus, irrigation can significantly increase the incidence and severity of root rots in eggplant. Increased frequency and duration of irrigation favor disease development.
Water, temperature, and soil texture are the major factors affecting the development of root rots. The presence of water is mandatory; soil saturation for as little as 5 to 6 hours can result in infection, and susceptible varieties can become severely diseased in as little as 5 days. Optimum temperature for plant infection is 75° to 92°F (24° to 33°C). Symptoms usually appear following a warm, wet period. Root rots are most serious in fine-textured (clay) soils that drain slowly and in highly compacted soils.
Management of root rots primarily depends on good soil and water management. Factors that influence the development of root rot in eggplants in a given season include amount and frequency of irrigation, soil compaction, and drainage. In fields that have low spots, plant on beds. Also, plastic mulch used with drip irrigation tends to result in wetter conditions in the soil around the roots and root rots may be more common under these conditions.
UC IPM Pest Management Guidelines:
UC ANR Publication 3470
J. J. Stapleton, UC IPM Advisor, Kearney Agricultural Research Center, Parlier
R. M. Davis, Plant Pathology, UC Davis