Wheat fungicide pre-harvest intervals

Tom Allen, Extension Plant Pathologist
By Tom Allen, Extension Plant Pathologist April 29, 2011 13:03

Wheat fungicide pre-harvest intervals

Over the past week I have continued to receive calls regarding the fungicide application restrictions in wheat.  The specific wheat pre-harvest intervals are set to reduce the likelihood of a residue issue at the elevator.  I do realize there has continued to be an increase in the level of disease present in the wheat crop, notably following the wet weather over the past 10-14 days.  However, even with regards to Fusarium head blight (or scab), the predictive model still does not suggest that we are under a high risk of the disease developing in any particular part of the state.  In fact, most areas in MS are still experiencing a low risk of the disease developing.  As I have said over the past few weeks, this is not a disease that we regularly encounter in MS.  Several pathologists have suggested they have never observed the disease in MS over the past 20 years. 

Application restrictions in wheat are quite specific on most fungicide labels.  Several of the labels clearly state a pre-harvest restriction of 10.5.  The specific growth stage, 10.5 is when heading is complete and immediately prior to the commencement of flowering.  At this time of the year, most fields I’ve observed are well beyond flowering (10.5.1) and thus beyond a time period when a fungicide could legally be applied for yield loss prevention.  Wheat specialists throughout the U.S. have suggested that they would not be comfortable applying a fungicide much beyond the commencement of flowering which in some cases, depending on environment, would more than likely be 30 days or less from harvest.  Typically, flowering requires from 3 to 5 days for completion so moving from 10.5.1 to 10.5.2 occurs quite quickly. 

At present, most of the wheat in MS is in Feekes Growth Stage 11 at any one of the specific stages that are generally referred to as ripening.  More specifically:

11.1 milky ripe

11.2 mealy ripe

11.3 kernel hard

11.4 harvest ready

The specific pre-harvest intervals for products labeled in wheat are as follows:

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Tom Allen, Extension Plant Pathologist
By Tom Allen, Extension Plant Pathologist April 29, 2011 13:03
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1 Comment

  1. jack cobb May 3, 14:08

    Tom, I work in the Charleston, MS area, and I have seen head blight in a few fields last week. One grower, on the edge of the hills, has 10% of one field affected with it. Originally, I thought this might be herbicide damage, as the West side of the field showed some glyphosate damage from a neighbors burndown. However, the symptoms appear to be exactly like the pictures of FHB i have found online. Just thought I would let you know. Jack

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