Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu
Hard to believe we are already approaching the end of September. Fungal disease pressure in small grains ended up being quite low for 2021, with very few cases of Fusarium Head Blight (FHB). It is hard to predict what in-season disease pressure will look like for 2022, but there are a few management decisions that can be made prior to planting. Here are a few items to consider:
Planting Date
While we do not typically observe Hessian flies, planting after the Hessian fly-free day is still a good reference point to reduce issues with viruses spread by aphids, like Barley Yellow Dwarf Virus (BYDV). While most of our fungal diseases were low in 2021, we did see a fair bit of BYDV around. Due to the sporadic nature of BYD infection, it is difficult to quantify yield loss, but studies have indicated around 0.5% loss of yield for each 1% increase in infection. If you are planting before the Hessian fly-free day, make sure to have a variety with tolerance to BYDV and follow IPM practices for aphid management. Early planting can also allow fungal pathogens more time to infect and overwinter. Seed treatments can be helpful for controlling soilborne seedling pathogens like Pythium, Rhizoctonia, and Fusarium.
Site Conditions
Small grains planted into corn stubble are at higher risk for FHB because the fungus is able to infect both corn and the small grain crop. The FHB pathogen can overwinter in corn fodder left in the field allowing for more rapid development and spread of spores under favorable spring conditions. When possible, planting small grains behind soybeans helps to reduce the amount of overwintering inoculum and risk of FHB the following spring. The logistics of timing soybeans that are ready for early harvest is a challenge, but could be worth planning for, especially with crops like malting barley. In cases where corn rotation is the only option, plowing under corn stubble or minimizing fodder at the soil surface before planting can help to reduce the amount of fungal tissue overwintering, but it will still be important to monitor spring weather conditions. If spring conditions are wet and humid during flowering, a fungicide application will likely be needed. The Fusarium Risk Tool wheatscab.psu.edu can be used to help aid in season fungicide decisions.
Variety
Variety selection is a key aspect of integrated disease management. In the case of wheat, varieties may have varying levels of resistance to powdery mildew, leaf rust, stripe rust, Fusarium head blight, and other diseases. When selecting your varieties, consider what diseases have been an issue in the past, and when possible, select resistant varieties to reduce the risk of disease development. Fusarium head blight remains one of the biggest disease concerns in our area. While complete resistance is not available, there are FHB resistance genes available in many wheat lines that provide partial resistance. Lines with partial resistance typically have reduced disease severity and lower levels of mycotoxin (DON) that accumulates in the grain. The University of Maryland conducts an inoculated misted nursery trial to test varieties for FHB/DON. In these trials, the fungal pathogen is added to the field prior to flowering and plants are misted daily to create the perfect environment for disease development. Wheat plants in this field are under a “worst case scenario” for disease, so FHB index and DON levels tend to be much higher than would be seen in a natural field setting, but this allows for separation of varieties to see which have the lowest levels of disease and DON content. 2021 results can be found at https://cpb-us-e1.wpmucdn.com/blog.umd.edu/dist/a/434/files/2021/07/2021-MD-wheat-varieties-disease-and-yield.pdf
Stands and Nutrition
High plant populations tend to create favorable environments for disease issues due to reduced airflow and increased canopy humidity. High levels of fertilizer promote lush, rapid growth that can favor disease; keeping fertility balanced reduces the chance of disease development.