Field Crop Disease Update - August 31, 2012

Published: August 31, 2012

Corn: With the hot, dry conditions over most of the state this season, corn foliage diseases have been minimal. There have been a few reports of pockets of southern rust and gray leaf spot but these diseases have not been as prevalent as the last few years.

The incidence of common smut has been slightly higher this year. Some of the smut galls on ears are quite large.

Ear and kernel rots have been the most prevalent of the corn diseases this season. Penicillium sp., Aspergillus flavus, Aspergillus niger, and Fusarium graminearum have all been found in corn fields throughout the state. Drought stressed corn, corn that died prematurely and corn with insect damage may have higher levels of these ear and kernel rot fungi. Rain over the Labor Day weekend may increase the incidence and severity of these fungi.

Black corn is showing up in many parts of the state and, again, rain over the Labor Day weekend may increase this problem. See article on “Black Corn” in this issue of the newsletter.

Corn stalk rots could also be a problem this fall. Fields should be checked for evidence of stalk rots and fields with stalk rot should be harvested as quickly as possible to prevent losses from lodging.

Soybean: The hot, dry conditions have also limited the development of soybean foliage diseases such as frogeye leaf spot, Septoria brown spot, bacterial blight and bacterial pustule. Cercospora blight causing the reddish-purple discoloration of leaflets from the tip in is showing up in low levels in some fields.

Symptoms of bean pod mottle can be seen on the young foliage of scattered plants in some fields. It is not as prevalent as the last few years. The soybean vein necrosis virus disease is quite widespread- see accompanying article in this newsletter.

There have some reports of SDS but both incidence and severity of this disease are low this season. In some fields there will be single, scattered plants showing the typical symptoms of SDS.

Damage from soybean cyst nematode may be more severe when soybean plants are stressed by hot, dry conditions. This fall would be a good time to sample fields and have samples tested for SCN population levels.