Plant Health Problems
The disease problems on turnip are similar to those of other Brassica. See Crucifers for a detailed discussion of the common diseases of this host.
Most of the insects infesting cabbage will occasionally feed upon turnip. See Cabbage.
The most important aphid infesting turnip is the turnip aphid, Lipaphis erysimi. It occasionally causes considerable damage to turnips, especially rutabagas. Other aphids that sometimes infest turnip are the green peach aphid and the cabbage aphid. See the Aphid fact sheet.
Cabbage maggot, Delia radicum.
The roots and underground stems of early turnip may be tunnelled by small, legless, white maggots, which cause the plants to wilt and be stunted. This insect infests the stems of early set cabbage and other crucifers. As a rule, late-planted cabbage is not injured, but late radish and turnip may be damaged. The white maggots infest the stems just below the surface of the soil and infested plants may wilt and die. The gray flies, which look like small house flies, appear about the middle of May and the females lay eggs on the surface of the soil near the stem of the plant. There are three generations each year, and the insect overwinters as pupae in the soil.
Covering plants with spun-bonded row cover or other fine-mesh material can keep the adult flies from being able to lay eggs on the plants. However, be careful to rotate the planting away from the ground where plants in the cabbage family have been grown before and to bury the edges of the cover. Beneficial nematodes that attack the maggots in the soil are available. Diazinon is registered for control of cabbage maggots in Connecticut. Consult the label for dosage rates, safety precautions, and preharvest intervals. When wilting or other damage is visible, it is already too late.