Heavy rains coupled with high winds made it difficult for growers in Delaware and Maryland to apply fungicides for Fusarium head blight (FHB) suppression. There has been discussion about waiting until this current weather front passes to make applications. Fungicide applications for FHB suppression are most efficacious when applied at the start of flower (when approximately 50% of MAIN tillers are flowering) until 5-6 days after this point. The reason this timing is most efficacious is because the main tillers compose the majority of overall wheat yields and FHB infection tends to be facilitated by extruded anthers containing pollen. If the fungus is active (i.e. producing spores due to several days of rain during or near the flowering phase) spores can colonize these anthers as well as glumes, and potentially move into grain, resulting in head bleaching and potentially chalky, shriveled grain. In addition, infection of the heads by FHB may result in elevated vomitoxin (DON) due to fungal activity. Research we have conducted with collaborators throughout the United States has shown that fungicide efficacy is maximized when the flowering to 6-days-post-flowering window is targeted. Efficacy tends to drop significantly when fungicides are applied outside of this window, although occasional exceptions do occur. Remember that DON is the major concern, and absence of FHB symptoms (i.e. bleaching) does not always mean reduced DON, but it may indicate an increased potential for elevated DON. If you missed your window for application due to rain and wind, and your field started to flower today, you should be able to make an application within 5-6 days without significant loss of efficacy.
For more information on FHB and fungicides, see a recent article I wrote for the Weekly Crop Update