Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu
Pythium Root Rot
This year has continued to have very conducive conditions for Pythium species. Symptoms can include stunted, slower growing plants, to severely infected, dead plants. Early in the season, we were seeing quite a bit of post-emergent damping off. Some of the symptomatic plants displaying symptoms of stunting have begun to set new brace roots and are growing out of the disease.
Anthracnose Leaf Blight
Anthracnose of corn is caused by the fungal pathogen Colletotrichum graminicola. Foliar symptoms typically include oval to irregular lesions on the lower leaves around V5-V8 that are brown/red-brown in color. Lesions often have concentric rings that can give a target like appearance. Using a hand lens, black hairs called setae can be observed and are usually diagnostic of Colletotrichum sp. This disease is residue borne and favored by no-till production and irrigation or natural warm, rainy conditions. Many hybrids are able to accumulate defensive chemicals and lesions are not observed after V6-V8. In a few weeks we will discuss Anthracnose stalk rot which can appear later in the season.
As the season progresses, if you are planning to make a fungicide application, the Corn Disease Working Group has updated the 2019 Fungicide Efficacy for Control of Corn Diseases which can be found at https://crop-protection-network.s3.amazonaws.com/publications/cpn-2011-corn-fungicide-efficacy-for-control-of-corn-diseases.pdf