Nathan Kleczewski, Extension Specialist – Plant Pathology; nkleczew@udel.edu
It is important that anyone who plans to use a recommended fungicide for scab suppression (Prosaro®, Caramba®, Proline®) understand that these fungicides will not result in control of scab similar to what you have seen for other pathogens such as rusts and powdery mildew. Due to variability with developmental stage of tillers and other factors, one can expect AT BEST around42-45% reduction in DON. Use of these fungicides does not guarantee that your DON will come in below the 2ppm dockage threshold. Below you will see a familiar table — the 10 year averages of 100 FHB tests conducted over an 11 year period. DON is what really matters with FHB. Levels exceeding 2ppm will be docked or downgraded to feed and level over 10 ppm can be rejected. Rejection is a rare occurrence, but it can occur.
The majority of FHB outbreaks are mild to moderate, meaning that DON levels will be well under the 10ppm “rejection” threshold. There will be situations (perhaps 20% of the time) that for some reason or another a field has exceptionally high DON, for example 30 ppm or above. In these cases the best case fungicide scenario would not reduce DON to a satisfactory level.
If you have serious concerns about FHB, you need to use an integrated management approach, and that starts with using a moderately resistant variety. One issue that has been brought to my attention is that scab ratings are often not available until September. We will work on this at a regional level to provide you with data gathered from variety trials and scab nurseries over the past 5 years to provide you with better guidelines for variety choices. Read my other article in this week’s WCU for information on how this resistance works and what to expect. The use of a good, moderately resistant variety and a scab fungicide can reduce DON by roughly 75%. This integrated approach will put you in a much more favorable position if you end up in a situation where DON levels exceed acceptable levels.
Things are starting to warm up, and there is a chance that rain is coming our way next week. Some fields ready to break boot may enter flowering around this period.
Table 1. Results of 100 Fusarium Head Blight uniform fungicide trials conducted in 14 states over a 10 year period.
From: Paul et al., 2008. Efficacy of triazole –based fungicides for fusarium head blight and deoxynivalenol control in wheat: A multivariate meta-analysis. Plant Disease 98:999-1011