2020 Corn Foliar Fungicide Efficacy Trials

Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu

Two foliar fungicide trials were conducted to evaluate fungicide efficacy in corn. Products were applied at V8 or R1 and plots were rated for foliar diseases and taken to yield. Click on the images below for pdf results of these trials.Results table

Results table continued


Grey Leaf Spot (GLS) was our most common disease at both sites. Symptoms began low canopy as small, tan, rectangular lesions with a yellow halo. At maturity, lesions are grey to tan in color, with a long rectangular shape (Figure 1); partially resistant hybrids can have more jagged margins than lesions on susceptible cultivars. Lesions often join to form large necrotic areas under favorable environmental conditions. Disease severity ratings were conducted by assessing the percentage of the ear leaf covered in GLS lesions. All fungicides tested reduced disease compared to plots that did not receive fungicide.

Figure 1: Rectangular lesion of Grey Leaf Spot on corn

This year a new disease, Curvularia leaf spot, also began to show symptoms around R4/R5. The range of Curvularia leaf spot in the US has been expanding in recent years. Symptoms start as small tan lesions with a brown/maroon border. These lesions resemble young grey leaf spot lesions, but when the leaf is flipped over and held up to the light, a gray center, prominent margin, and yellow halo can be observed (Figure 2). Ratings of Curvularia leaf spot were conducted at the Warrington site as symptoms became widely present 42 days after fungicide application. This disease is favored by excessive dew and sporadic rainfall, which aligned well with our August and early September weather patterns. While there were some differences among products, this disease does not seem to respond to fungicides as readily as GLS. There are not currently any fungicides that list Curvularia on their label. There have not been any reports of extreme yield loss from Curvularia in the US, but the impact of this disease is not yet fully understood and we will continue to monitor its presence in the Mid-Atlantic.

Figure 2: Corn leaves with grey leaf spot and Curvularia leaf spot. Left image top side of leaf, right image underside backlit with sun.