Cause The fungi or fungus-like microorganisms, Pythium debaryanum, Globisporangium ultimum (formerly P. ultimum), Fusarium spp., and Rhizoctoniasolani, attack young seedlings of many vegetables, including members of the genus Brassica.
Cause Deficiency or unavailability of boron in the soil and subsequent deficiency in the plant. All vegetables require boron for growth, but the amount required varies considerably. Turnip, rutabaga, and cauliflower are sensitive to boron deficiency, which is common in soil that is alkaline or sandy and subject to excessive leaching. In any soil, boron also may become less available during long droughts.
Cause Aphanomyces raphani, a fungus-like microorganism that overwinters in soil and on diseased plant residue in soil. It invades the fine rootlets of young seedlings and develops resting spores in large numbers within the roots.
Turnip with black leg leaf spots (center) at a later stage; note the tiny black pycnidia that dot these mature leaf lesions. Most of the leaf spots to the left side of the leaf are white leaf spot.
