Alyssa Koehler, Extension Field Crops Pathologist; akoehler@udel.edu
September is flying by and small grain planting is only a few weeks away. Fungal disease pressure in small grains was moderate in 2023. It is hard to predict what we will see in 2024, but there are management decisions that can be considered prior to planting:
Planting Date: While we do not typically observe Hessian flies, planting after the Hessian fly-free day (Oct 3 – New Castle County; Oct 8 – Kent County; Oct 10 – Sussex County) is still a good reference point to reduce issues with viruses spread by aphids, like Barley Yellow Dwarf Virus (BYDV). 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. Typically we associate fall infections as more damaging to yield potential than spring infections. However, in 2023, we did end up with a lot of aphid activity in February due to the mild winter and saw some significant stunted areas from BYDV, particularly in malting barley (Figure 1). While we cannot control what happens once planted, planting date is more in our control. If you are planting before the Hessian fly-free day, make sure to select 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.
Figure 1: Stunted yellow patches due to Barley Yellow Dwarf Virus
Site conditions: Small grains planted into corn stubble are at higher risk for Fusarium Head Blight (FHB) because the fungus (Fusarium graminearum) 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 reduces 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 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 deciding what varieties to plant, 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 the most concerning disease in our area. While complete resistance is not available, many wheat lines have FHB resistance genes that provide partial resistance. Lines with partial resistance typically have reduced disease severity and lower levels of mycotoxin (DON) accumulation 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. 2022 results can be found at https://cpb-us-e1.wpmucdn.com/blog.umd.edu/dist/a/434/files/2022/07/2022-wheat-and-barley-disease-ratings.pdf and 2023 results should be released soon.
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.
By keeping these factors in mind, you can hopefully get your crop off to a healthy start and have less disease pressure in the spring.