How to Manage Pests
UC Pest Management Guidelines
Soft rot. Symptoms of soft rot include rotted tissues that are wet, cream to tan in color, and soft. Rot begins on the tuber surface and progresses inward. Infected tissues are sharply delineated from healthy tissue by dark brown or black margins. Shallow necrotic spots on the tubers result from infections through lenticels. Rotting tissue is usually odorless in the early stages of decay, but develops a foul odor as secondary organisms invade infected tissue. Soft rot can also infect wounded stems and roots.
Blackleg. Plants with blackleg are stunted and have a stiff, erect growth habit. Foliage becomes chlorotic and the leaflets tend to roll upward at the margins. Plants may wilt. Stems of infected plants exhibit an inky black decay. The base of the stem is often completely rotted. In relatively dry soil, only the pith may show blackening. Tuber symptoms for blackleg are similar to those of soft rot. The soft rot Pectobacterium spp. may cause wilting but affected plants lack the characteristic inky black stem decay.
Soft rot. Bacteria are present on all tubers and are associated with many kinds of plants. Infections in the field are favored by high soil moisture and high temperatures. Other factors include anaerobic conditions, enlarged lenticels, and invasion by other pathogens. Bacteria enter lenticels, growth cracks, or any injury. During and after harvest, soft rot is favored by immature tubers, adverse temperatures (pulp temperatures above 70°F at harvest), mechanical damage, and free water on tuber surfaces.
Blackleg. Blackleg inoculum comes primarily from infected seed tubers, but it may also be spread in infested soil, contaminated irrigation water, and by insects. Blackleg is favored by cool, wet conditions at planting followed by high temperatures after emergence.
The pathogens that cause these diseases occur wherever potatoes are grown. The severity of the disease depends on seed-handling techniques, soil moisture and temperature at planting, environmental conditions, cultivar, amount of infection in the seed lot used, and external sources of the bacteria such as irrigation water and cull piles.
Blackleg. Use pathogen-free tubers for seed. Warm seed tubers to about 55°F before planting. Provide good drainage and do not over irrigate. Eliminate cull piles and potato volunteers in rotation crops and adjacent fields.
UC IPM Pest Management Guidelines: Potato