Wheat in southern parts of MD and DE, as well as some early flowering varieties, began flowering the latter half of last week and most of the remaining wheat I expect to flower sometime in the next 7-10 days, depending on temperature. Flowering occurs when 50% of the main tillers have started to produce yellow anthers from the center of the heads. This comes at a time when we have received an inordinate amount of water, resulting in elevated levels of Fusarium Head Scab Risk for flowering wheat fields.
Over 300 replicated university trials conducted over multiple states and 19 seasons have shown that the application of Caramba, Prosaro, and Proline at flowering can reduce FHB severity and DON on average of 50% and 45%, respectively, relative to untreated, inoculated checks. That means that if you have an FHB outbreak and 20% of your heads are infected, resulting in 5 ppm DON, these products may bring down your levels to 10% severity and 2.75 ppm DON. The use of moderately resistant varieties will further reduce disease and DON, on average, 45%. In the same scenario, the MR variety would start with 11% infected tillers and 2.75 ppm DON. The application of a fungicide to this variety would potentially reduce infected tillers to 5.5% and DON to 1.23 ppm.
Additional replicated university research indicates that a moderately resistant wheat variety reduces DON compared to a susceptible check (e.g. Shirley) by roughly 45%. Some varieties I see planted this year were sold as moderately resistant based on visual ratings, but not DON. When looking at the DON, I would categorize some of these as moderately susceptible- better than a susceptible variety but not as good as moderately resistant variety. Remember, visual symptoms only predict DON about 60-70% of the time and that FHB can elevate DON in healthy looking kernels. Always start your variety selection by assessing DON levels compared to a susceptible check, then rank by visual symptoms, or index.
Fungicides for FHB suppression should be applied from the start of flowering, but can be applied 5-6 days from this point without significant loss in efficacy. Again, this comes from recent, replicated university trials conducted across environments and varieties. If your field started flowering and conditions are not ideal for making an application, know that you have a few more days.
The forecast is calling for an increase in temperatures next week and I expect the risk of FHB to remain moderate to high in both suceptible and moderately suceptible varieties. Stripe rust shuts down when temperatures exceed 69° F. Powdery mildew slows as temperatures increase. Increases in temperature and low levels of relative humidity in the upper canopy can limit development of powdery mildew to lower portions of the plant, which contribute little to yield after stem elongation. Relative humidity, not water or leaf wetness, determines the level of infection by the powdery mildew pathogen in susceptible varieties. Recent cool temperatures have limited the development of our most common foliar diseases, the leaf blotch complexes. These may increase with warming temperatures provided we receive adequate amounts of rain. Fortunately Prosaro, Caramba, and Proline will provide good control of the aforementioned diseases.