Monday, May 4, 2009

Current Status of Fusarium Head Blight

Low temperatures and breaks between rain events (up until this past event) have kept the FHB predictive model from indicating even moderate FHB risk (up until now). The block of rain we have just experienced has changed that, so the FHB models are now showing moderate to high risk for spore release in much of central and west KY. I believe conditions will be ripe for spore release beginning Monday night. Spore release happens mostly happens at night and is actually favored more by high humidity than rain. Rain can give you splashing of spores, but it also washes spores out of the air and off of plants. Infection, on the other hand, requires free moisture, so infection generally is greater when spores have been released and transported to heads during dry, but humid, periods at night, followed by rain the next day or so to support infection. It is complicated and that is why we don't always have a lot of FHB. It is rather hard to get!

I encourage growers with decent crops that are just entering flowering to to spray as much as they can Monday and Tuesday and into Wed. I realize that getting sprayers into fields will be hard, so that is a complicating factor that may prevent many fields from being sprayed this year. It is what it is. More wet weather is anticipated beginning Wednesday. I have had several questions asking about how late one can spray and still get FHB suppression. That is pretty simple. Most labels restrict application to early flowering or at most 50% bloom. Thus, there is not much of a decision to make. The days to harvest restriction is very specific for all fungicides labeled for wheat.

The key thing to remember is that according to the FHB models, up to the present moment, not many spores have been available to spread to heads, let alone infect heads. But after today and the gloves come off unless it turns hot and dry fast. This could be a bad FHB year in light of the lack of spraying and/or difficulty in getting fields sprayed. But the timing of this rain coinciding with the completion of head emergence or flowering in many fields is hard to deal with. If fields had sprayed before the rain, it might have been too early to get good coverage on the heads.

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