Cabbage and Cauliflower (Brassica sp.)-Phytophthora Root Rot

Cause Phytophthora megasperma is a fungus-like microorganism that survives as resistant spores in the soil and infects its hosts with swimming zoospores under wet conditions. All crucifer crops are susceptible as are most cruciferous weeds.

Symptoms Leaf margins discolor, turn brown, and eventually die. Aboveground portions of the plant wilt, and plants may die. Lateral roots are absent or entirely decayed. Tap roots are entirely decayed or show large, dark lesions along their entire length. Symptomatic plants are found in wet areas of the field.

Cultural control

  • Plant only on well-drained soil that has a minimum of low areas where water can accumulate.
  • Avoid excessive irrigation.
  • Practice a 3-year rotation with nonsusceptible crops.

Chemical control Treat the seedbed.

  • Ridomil Gold SL may be banded or surface-applied at 1 to 2 pints/A. Band-rate determinants include band width and row spacing; see label. Incorporate 2-inches deep when used. 48-hr reentry.

Biological control

  • Double Nickel LC at 0.5 to 4.5 pints/A for soil application on 14- to 28-day intervals. Can be applied the day of harvest. 4-hr reentry. O