Field Crop Disease Update- August 7, 2006
By Laura Sweets

Corn
Field crop diseases on corn have been rather quiet for the last few weeks. Earlier in the season, Stewart’s bacterial wilt, common rust, anthracnose and gray leaf spot were present in low levels in scattered fields across the state. However, the extended period of hot, dry weather as slowed the development of these foliage diseases and in most fields the ear leaves look quite clean.

With the extended high temperatures and dry conditions some fields are starting to turn. Initial symptoms of stalk rots could be present in these fields. See accompanying article on corn stalk rots.

Soybean
Brown spot continues to be evident in the lower canopy of many fields and downy mildew has been quite common in the upper canopy of many fields. Downy mildew symptoms include light to bright yellow blotches on the upper leave surface with tufts of grayish-purple mold growth on the lower leaf surface beneath the yellow blotches.

Sudden death syndrome has been showing up in some fields. The foliage symptoms, ie. yellow blotches between the veins with the veins staying green can be very striking. The entries in the SDS trials at Columbia and Waverly are showing a wide range of symptoms. Some entries have no visible symptoms, some are showing light yellow blotches between the veins on leaves in the upper canopy and other entries are showing severe foliage symptoms. These two trials were planted in mid-April and have been irrigated over the season.

We are also still receiving reports of plants dying from Phytophthora root rot and plants showing severe stunting and yellowing from Rhizoctonia and/or Fusarium root rot. At this point in the season there are no managements options for these root rot diseases.

Laura Sweets
573-884-7307