By Pierce Paul and Dennis Mills, Ohio State University Extension
1 – Fungicide application at FLAG LEAF EMERGENCE, BOOT, or ANY TIME BEFORE HEADING WILL NOT CONTROL SCAB or VOMITOXIN.
2 – The head scab fungus infects when the wheat crop is flowering i.e., when anthers are seen sticking out of the heads, causing scab to develop and producing vomitoxin.
3 – Therefore, fungicides need to be applied to protect the flowering head to reduce infection, scab development, and vomitoxin production.
4 – Between flag leaf emergence and boot, the head is in the leaf sheath of the flag leaf where it is protected from the head scab fungus, so scab will not cause a problem while the head is hidden, even during these constant rains.
5 – Between flag leaf emergence and boot, the head is in the leaf sheath of the flag leaf where the fungicide will not reach it. These fungicides need to be applied like a protectant – ON THE PLANT PART just prior to infection. THIS PLANT PART FOR SCAB control is the WHEAT HEAD WITH ANTHERS HANGING OUT. So, if it becomes wet and humid after the heads emerge when the crop is at greatest risk for scab, applications made before flowering WILL NOT PROVIDE PROTECTION.
6 – Fungicide application between flag leaf emergence and boot will provide EXCELLENT CONTROL OF LEAF DISEASES BUT NOT SCAB.
7 – Fungicide applications made at heading (when the heads are fully emerged) will provide some suppression of scab, but are much less effective than applications made at flowering.
8 – For scab and vomitoxin control, application by air may be the only option if it is too wet to get into the field, but THESE APPLICATIONS NEED TO BE MADE AT FLOWERING, USING A VOLUME OF 5 GALLONS/ACRE AND GETTING AS CLOSE AS POSSIBLE TO THE WHEAT CANOPY.
9 – APPLICATION BY AIR BEFORE FLOWERING is even LESS EFFECTIVE FOR SCAB control; quite frankly IT DOES NOT STOP SCAB.
10 – So, if you are targeting leaf diseases, applying a fungicide at this time may be an excellent idea, given the wet weather that we have had.
11 – However, if you are truly concerned about scab and vomitoxin, which is understandable after last year’s problems and the weather we have had so far, applying a fungicide now (before flowering), is both a waste of time and money. You will need to make another application at flowering to control scab.
12 – Read product labels for proper timing, since not all fungicides can be applied as late as flowering.