Diseases reported in corn and soybean

This information was summarized from a July 10, 2000 teleconference with Iowa State University Extension field specialists in crops.

  • Northwestern Iowa has been missed by much of the recent rainfall and some counties have received less than 5 inches of rain since April 1. Corn and soybean plants are showing drought stress, especially in Woodbury, Plymouth, Cherokee, and parts of Sioux and O'Brien counties. In other areas, up to 6 inches of rain was reported during last evenings' thunderstorms.
  • Crops generally look good. Corn is tasseled, except for in the northeastern counties where some corn is very uneven and growth stage is V11 to V12. Most of the field specialists reported a few fields with uneven stands or stunted corn plants. Some stunting may be caused by potassium deficiency (lower leaves yellowing and then browning as tissue dies along margins). Other reasons for stunting cannot be pinpointed and more samples are being tested to help determine the cause of the problem. Few European corn borer and some flea beetle sightings were reported.
  • Diseases showing up in corn include common rust, eyespot, Stewart's disease, and anthracnose. Some seed fields will probably need spraying for common rust. Eyespot and common rust are occurring earlier than normal and seem to be more widespread than in past years.
  • Growth in some soybean fields has been slow and the plants haven't developed their typical dark green color. Soybean cyst nematode, sudden death syndrome, rhizoctonia, and brown stem rot were reported. The first generation of bean leaf beetles is beginning to emerge.
  • Second-cut alfalfa harvest is complete across most of the state. There hasn't been a lot of potato leafhoppers spraying reported, but some fields are reaching high populations of nymphs.
  • The oat crop is starting to ripen and will be ready to harvest in the next 10 days. Some lodging was reported in north central fields. Winter wheat harvest is continuing, with one yield in south central Iowa reported at 85 bushels per acre.

This article originally appeared on page 138 of the IC-484(18) -- July 17, 2000 issue.

Updated 07/16/2000 - 1:00pm