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Thursday, Jan. 19, 2017

Diplodia showing up in some area cornfields

Posted Monday, August 9, 2010, at 5:51 PM

The warmer weather has allowed the crop to advance rapidly. As of August 1, 92% of the corn was silked or beyond. Fifty-three percent of the corn was in the dough stage with 10 percent dented. Also, soybean blooming and beyond was 66 percent complete with thirty percent of the plants setting pods.

The early planted corn is looking fairly well, but a few problems are still showing up. Diplodia ear rot is showing up in several fields with reports of up to 10% coverage in some fields. Reports of Diplodia are primarily from southwest and west central Missouri. If Diplodia occurs soon after pollination, it will be evident as a bleaching or light straw coloration of the ear leaf and husks on the ears of infected plants. The most characteristic symptom of Diplodia ear rot is seen when the husks are peeled back revealing a dense white to grayish-white mold growth matted between the husks and the ear and between the rows of kernels. Symptoms often start as the base of the ear. Diplodia can also cause a stalk rot of corn.

Management options for Diplodia are limited. Crop rotation is extremely important because the primary source of inoculums is diseased corn debris left in the field. Hybrids differ in their susceptibility to Diplodia ear rot. Check with your seed rep on susceptibility to Diplodia. Diplodia ear rot is not listed on the majority of foliar fungicides labeled for corn. Timing of application in relation to stage of growth and weather conditions would be crucial for fungicides to provide suppression. Good coverage of ears may be difficult to achieve. Generally, fungicide applications are not going to provide acceptable control of Diplodia ear rot, according to Laura Sweets, University of Missouri plant pathologist.

In soybeans, webworm still seems to be a problem in areas. Reports that I have received seem to indicate that they are more prevalent on later planted soybeans than on the earlier planted fields. Treatment is justified when 10 to 12% of plants show heavy webbing on top leaflets or when defoliation reaches 30% before bloom or 20% from bloom to pod fill.

There have also been calls about "yellow soybeans". It is important to dig plants and examine their roots. With the cool, wet conditions this spring and the continued wet conditions through the season in many parts of the state, soybean plants may have very poor root systems. The root mass may be poor, the root system very shallow with lateral roots close to the soil surface and running almost parallel to the soil surface and the roots may be very small to virtually non-existent. Plants with such poor root systems may be unable to take up available nutrients so might be exhibiting nutrient deficiency symptoms. Cooler temperatures with adequate moisture would help this situation.

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As our local University of Missouri Agronomy Extension Specialist, Crook has been writing a column for the print edition Agriculture page for the past three years and we will now be sharing it on our web version. Crook has a bachelor and masters degree in agronomy from University of Missouri and received his doctorate in Agronomy from Kansas State University. He was in soybean variety development research for 22 years for various seed companies and has been Saline County's agronomy specialist for 10 years.
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