Wheat Scouting Update and Disease Thresholds

A check of our research studies found that the wheat crop is at the Feekes 6 and 7 growth stages (first and second nodes) across the state. This is an important time to be out in the wheat and scouting to determine if the use of a foliar fungicide will be needed as we move into flag leaf emergence (Feekes 8). The flag leaf is the most important leaf, accounting for upwards of 50% or more of the final yield and a goal with the use of a foliar fungicide is to protect this leaf. Most of the questions to date have been about powdery mildew. Susceptible varieties are showing significant disease pressure as warm March temperatures contributed to lush vegetative growth and in some cases pre-jointing lodging.

Looking ahead, there exist some thresholds as you scout at Feekes 7 and 8 to determine if a foliar fungicide may be warranted.

At Feekes 7, the thresholds are:

Powdery mildew: check the uppermost leaf - the threshold is an average of five pustules per leaf.

Wheat leaf rust: check any leaf - the threshold is an average of one pustule per leaf.

Septoria leaf blotch: check the uppermost leaf - the threshold is 25% of the leaves having expanding blotches

At Feekes 8, the thresholds are:

Powdery mildew: check from the flag-2 leaf (2nd leaf below the flag leaf) and upward - the threshold is an average of five pustules per leaf on the flag-2 leaf.

Wheat leaf rust: check from the flag-3 (3rd leaf below the flag leaf) and upward - the threshold is an average of one pustule per leaf on the flag-3 leaf.

Septoria leaf blotch: check from the flag-2 and upward - the threshold is 25% of the leaves having blotches

If you note disease in the lower canopy but not on any of the leaves discussed above, consider increasing the frequency of your scouting to determine if there is evidence of new pustules or blotches moving into the upper canopy.

For further information regarding factors to consider for determining the need for a foliar fungicide recommendation, please check here.

For information regarding the efficacy of several foliar fungicides against different wheat diseases, please check here.

Results across our different studies the past few years have indicated that the best response to a foliar fungicide application has occurred when powdery mildew was the target and the wheat variety was susceptible. When the wheat variety was resistant to powdery mildew, we have not seen a consistent response, if at all.

Updated Wheat Fungicide Table

With wheat growth and development ahead of normal in 2012, it is important to pay attention to the growth stage when determining if there is a need for the use of foliar fungicides. Active scouting is important to determine which diseases are present and either the incidence and/or severity of each disease relative to wheat growth stage. To help in understanding the efficacy of different fungicide active ingredients, the NCERA-184 (Management of Small Grain Diseases) committee reviews and updates the Fungicide Efficacy Table for Control of Wheat Diseases each year. Ratings for different active ingredients are provided and range from poor to excellent for the following wheat diseases: powdery mildew, Septoria leaf blotch, Stagonospora leaf/glume blotch, tan spot, stripe rust, leaf rust, stem rust, and head scab. These ratings are based on results and observations from trials conducted across different locations (i.e., states) and years and is meant only as a guide. It is important to read and follow the label carefully regarding application timing and recommended rates against different diseases.

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