What diseases can affect root crops?
Listed below are several diseases that most frequently occur on root crops. Symptoms are described briefly. Colored pictures of disease symptoms can be seen in the publication "Identifying Diseases of Vegetables" available from the Penn State Publication Distribution Center, or from extension offices.
Cercospora leaf spot of beets: These spots usually are brown or gray with a purple border. THey usually develop late in the season. Most beets are resistant.
Control: Follow a 2-3 year rotation. Remove refuse from the garden as soon as beets are harvested. If necessary, fungicides can help when applied as labelled.
Leaf spot and root canker of parsnips: Spots develop on leaves and dead canker areas develop at the top of parsnip roots. Disease is promoted by wet conditions.
Control: Practice at least a 2-year rotation. Provide good drainage of soil. Lime soil to ph 7. Ridge soil over shoulders of the roots.
Leaf spots of carrots: Lower leaves become spotted and may die.
Control: Grow carrots in a sunny location. Avoid growing carrots in the same area during successive years. When a leaf spot problem is anticipated, labelled fungicides can be helpful if started when symptoms first appear. Remove carrot tops from the garden at harvest; the tops can be composted.
Root knot nematodes: Nematodes are microscopic worms that live in soil. The root knot nematode causes small swellings to develop on the side of the main root and on fine roots.
Control: Rotate crops in the garden. Avoid planting susceptible crops during successive years. Susceptible crops include carrots, parsnips, tomatoes, lettuce, and cucurbits. Sweet corn is seldom affected and is a good crop for affected areas.
Clubroot of turnip: Roots become swollen and distorted and leaves may wilt.
Control: Avoid areas where turnip and cabbage related plants were grown within 7 years. If clubroot has been a problem during past years, apply hydrated lime (1 lb for 30 square feet) in the spring before preparing the seedbed. Remove plants including roots as soon as harvest is completed. Do not compost roots that have clubroot symptoms; discard them.
Dr. Alan A. MacNab, Professor, Plant Pathology
Penn State College of Agricultural Sciences
211 Buckhout Lab, University Park, PA 16802
Reviewed: June, 2003
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