Using fungicides to help suppress wheat diseases

A new information piece summarizes the effectiveness of various fungicides in suppressing diseases in wheat.

Fungal diseases of the foliage and heads of wheat continue to be a significant limitation to profitable crop production. Fungicides have proven to be effective in reducing potential losses in grain yield and quality. However, the costs of fungicide applications need to be carefully weighed against the benefits, particularly with lower commodity prices.

There are several effective fungicides available. University pathologists from the north-central states have created a listing of fungicide products along with ratings indicating their effectiveness against specific leaf and head diseases: Fungicide efficacy for control of wheat diseases, 2018. As the table outlines, several products contain two or three chemistries to provide multiple modes of action. These are generally recommended for use at or before flag leaf extension. Once heads and flowers emerge, triazoles, such as Caramba and Prosaro, are recommended to target both head scab and late-season leaf diseases. (Using strobilurin chemistries at heading are discouraged, as they are not labeled and can lead to higher toxin levels related to Fusarium head scab.)

The table also lists several diseases found in the north-central states. The most significant fungal disease for Michigan growers included powdery mildew, Septoria leaf blotch, stripe rust, leaf rust and head scab. Based on the experience of the past two seasons, stripe rust deserves particular attention, as many varieties are relatively susceptible to this aggressive disease (see “Stripe rust susceptibility of Michigan wheat varieties”).

The cost of wheat fungicides might range from $4 to $16 per acre depending on the product and application rate. Additional expense would include application costs and, in some cases, traffic loss. Consequently, one might need several bushels per acre of additional grain in order to recover the investment. This level of yield response can usually be attained in high yield environments, particularly when the fungicides are used in the latter part of the season on susceptible varieties.

Where the cost is most difficult to recover is when yields are limited by soil types or other environmental factors. For these fields, emphasis might better be on selecting varieties with a strong disease resistance package, avoiding excessive fertilizer nitrogen rates, and using fungicides sparingly and only when field scouting points to a significant threat of disease.

When scouting wheat fields and contemplating fungicide use, it is important to pay particular attention to the flag leaf. The goal is to keep this last leaf as free of disease as possible throughout the flowering and grain-fill periods. To achieve this, a fungicide may be warranted during or soon after the flag leaf stage. In many cases however, the application can be postponed until heads have emerged and flowering has begun. This timing, which is the most widely used in Michigan, reduces the risks of grain yield and quality losses from both leaf diseases and Fusarium head blight.

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