Cause Phytophthora megasperma 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
- Warhammer (chitosan) at 4 to 12 fl oz/A on 7- to 14-day intervals. Studies at the University of Florida showed a reduction in disease severity for Phytophthora blight in squash when chitosan was applied as a 1% soil drench. No preharvest interval or reentry interval requirement.
Biological control Efficacy unknown in Oregon.
- Bexfond at 7 to 14 fl oz/A. O
Reference Mo, X., and Zhang, S. 2013. Effect of chitosan, Heads Up and TiO2 on Phytophthora blight in squash, 2012. Plant Disease Management Reports 7:V081.