Cabbage and Cauliflower (Brassica oleracea)-Nematode, Cyst

Cause Cyst nematodes (Heterodera schachtii) are sedentary endoparasites.

Symptoms First field symptom is the appearance of small, conspicuous areas where plants are stunted. Later in the season, these areas are marked by absence of plants and presence of weed patches. In severely infested fields, areas of decline usually can be identified by excessive leaf wilting during hot weather. Affected areas increase in size with continuous cropping of host crops.

Infected plants are much smaller than normal ones. Frequently, they have a dense system of secondary roots, called a hairy-root condition. Examination with a hand lens usually shows numerous small, white, bead-like structures on roots of infected plants. These structures are lemon-shaped and later become cysts containing eggs that develop into future generations of nematodes.

Sampling Soil for cabbage production can be examined for this pest by a simple field test. Place a teaspoonful of soil in a glass of water, stir briefly, and allow debris to float to the surface. You can see and recognize any brownish cysts that adhere to the sides of the glass. This test will not predict severity of infestation but will show the field has a nematode population. Negative results do not necessarily mean the field is free of nematodes because test accuracy depends on the number and distribution of samples collected.

Infective second-stage juveniles, adult males (rarely), and cysts (the dead body of the female, which contains eggs) can be obtained from soil samples submitted to nematode diagnostic labs. However, cyst extraction requires a special procedure; noted on the form that accompanies the sample whether a cyst count is desired. During the growing season it is helpful to send roots as well as soil to assist the diagnosis.

Cultural control

  • Crop rotation is an effective way to reduce nematode population because the pest has a narrow host range. In addition to sugar beets, other hosts are mangel-wurzel, table beet, cabbage, cauliflower, Brussels sprouts, broccoli, rape, turnip, rutabaga, and radish. Weed hosts are dock, knotweed, lambsquarters, mustard, nightshade, purslane, saltbush, and red root. Any of these that survive from year to year may act as reservoirs for the pests, counteracting much of the value of crop rotation. Crops that may be used in a short-term rotation include beans, sweet clover, corn, grains, peas, potatoes, and tomatoes. Alfalfa is suitable for a long rotation period. Length of rotation period should vary with severity of nematode infection. Slight infestations may require only a 2-year program; severe infestations require a 5- to 6-year interval between host crops.
  • Do not return crop refuse to fields that may be used for host crops in the future.

Chemical control Soil fumigation.

  • Telone II at 18 gal/A broadcast to mineral soil. . Use higher rates for soils with 20% or greater organic matter. Note: To avoid excessive salinity and nitrogen, use fertilizer rates as indicated by soil tests made after fumigation. 5-day reentry. See label for further details. Restricted-use pesticide

Biological control

  • MeloCon WG at 2 to 4 lb/A at 4- to 6-week intervals for nematode suppression. See label for specific application types and timings. 4-hr reentry. O