How to Manage Pests

Pests in Gardens and Landscapes

Pink root—Phoma terrestris

Pink root is primarily a problem on onion; garlic is also infected by the fungus but is not affected at an economically important level. Roots of plants infected with pink root first turn light pink, then darken through red and purple, shrivel, turn black, and die. New roots also may become infected and plants may become stunted. Infection is confined to the roots, and death seldom results.

Life cycle

The fungus that causes pink root is a common soil inhabitant that penetrates roots directly; wounds are not necessary for infection, but weak plants are more susceptible. The pathogen can persist in soil indefinitely; the longer plants are grown in the garden, the more destructive the disease becomes. The fungus can be spread in water or on dirty equipment. Optimum temperatures for disease development are 75 to 85°F.

Solutions

Prevention and control of pink root include use of resistant varieties, good soil fertility, and control of insects and other diseases to maintain healthy plants. Rotate out of garlic or onions to reduce the severity of the disease. Soil solarization may help to reduce disease levels in the soil before planting.

 

Discoloration of onion roots
Discoloration of onion roots

Healthy bulb (left) and infected bulbs
Healthy bulb (left) and infected bulbs


Statewide IPM Program, Agriculture and Natural Resources, University of California
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