Field Crops Plant Pathology Winter Recap, 2021 Nematode Surveys and Small Grain Disease Observations

Alyssa Koehler, Extension Field Crops Pathologist;

It is hard to believe we are already in March. Over the winter, the UD Plant Pathology lab (find us @UDPlantPath) has been busy working on lab and greenhouse projects. In 2020, we began research to better understand Pythium species in corn. Symptomatic seedlings were brought back to the lab and over 13 species have been identified to date. We are currently screening these species in the greenhouse to compare aggressiveness. Results from the first trial showed varying aboveground symptom development from limited (Figure 1) to quite a bit of stunting (Figure 2) depending on the species. The second round of trials is in progress and we will keep you posted as we complete greenhouse and in vitro fungicide trials to develop best management recommendations for each of these species.

Figure 1. Healthy control (left) versus corn seedling(s) infected with Pythium graminicola (right)

Pythium inflatum

Figure 2: Healthy control (left) versus corn seedlings infected with Pythium inflatum (right)

Nematode Management
Another focus of the lab is nematode management. Initial surveys of soybean fields in 2019 and 2020 showed that Soybean Cyst Nematode is widely present and there are numerous fields with elevated levels of Root Knot and Lesion nematodes. We will be continuing nematode survey sampling for soybean in 2021 and adding corn sampling. If you have soybean or cornfields with suspected problems and would like to be added to the survey, please let me know at

Small Grain Disease Observations
Small Grains are on the horizon. We will dive into management of the most economically important diseases for our region in future articles. As fields dry enough to get out for a first nitrogen application, that is a good opportunity to scout for diseases like powdery mildew. However, we typically do not observe powdery mildew until temperatures are above 59-60°F for 1-2 weeks. If it stays cold, it will likely be a few weeks before powdery mildew has a chance to “wake up”.

Observation Times for Common small Grain Diseases in the Mid-Atlantic




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