Lime soil to ph 7. Ridge soil over shoulders of the roots. 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.
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. 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. Roots become swollen and distorted and leaves may wilt.