Thursday, May 28, 2009

Wheat Crop Condition Declining Due to Disease

Considerably more head scab (FHB) has appeared this week across KY. The wet May we have just experienced has apparently provided for multiple infection periods and an extended window for symptom expression. A properly timed and sprayed fungicide application appears to have made a significant difference in FHB compared to where fields were not sprayed. But it would be unreasonable to think the benefit exceeds 50% control in any field. Modern fungicides simply are not that good against FHB, even when application and timing are ideal. Hopefully the benefit associated with spraying will carry over into DON levels at harvest. Control in fields that were sprayed too late (post infection) is poor (as expected).

Stagonospora leaf and glume blotch are also getting quite severe in many fields and I am starting to see a lot of leaf rust, even in fields that were sprayed (fungicide protection is wearing off). In some cases, leaf and glume blotch are quite severe in treated fields. While modern fungicides do an excellent job in managing leaf and glume blotch, fungicide must be applied before infection occurs. In many fields, applications timed properly for FHB control (early flowering), were probably too late to achieve good leaf and glume blotch control. The fact is, the main infection period for both diseases can be the same, but many times is not. This year, fields treated while the heads were emerging seem to show the best control of leaf and glume blotch.

Many (most?) years it is hot and dry by the time we get to the end of May. Not this year. Our wheat crop is steadily declining and will probably continue to do so until harvest maturity is reached.

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