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Expectations of Fungicides Applied to Wheat at Flowering under Dry Conditions (07/13/17)

Severe Fusarium head blight problems over the past couple growing seasons have plagued durum and spring wheat growers in northcentral and northwestern North Dakota.

Expectations of Fungicides Applied to Wheat at Flowering under Dry Conditions

Severe Fusarium head blight problems over the past couple growing seasons have plagued durum and spring wheat growers in northcentral and northwestern North Dakota. This year, the field conditions are drier, with less rainfall and lower humidity than previous years, resulting in a lower scab risk. However, there are questions pertaining to the value of applying a fungicide for yield and test weight protection. To help answer this question, I examined research data since 2011 to find situations where fungicides were applied at flowering in an environment with low scab risk and low fungal leaf spot incidence. After sorting the data, 14 trials were conducted under low disease environments. From these trials, the yield and test weight data from Prosaro and Caramba applications at flowering were compared to the non-treated control. Tebuconazole data was available from one trial, but the data was not used due to lack of observations across years. In addition, since Prosaro and Caramba treatments did not appear in each trial, the data was combined and was not individually separated. Yield responses of fungicides applied at flowering under low disease environments were highly variable. When compared to the non-treated control, mean yield values of flowering fungicide applications were 2.8% higher and ranged from -9.2% (no response) to 9.3%. For test weight, differences were negligible (mean value of 0.01%), with a range of -1.8% (no response) to 0.6%. For both agronomic traits, a fungicide applied at flowering under low disease environments does not provide a consistent response.

The next question is how to interpret the data? First, fungicides applied at early-flowering are used to help manage scab and DON/VOM under environments of elevated scab risk (prolonged periods of moisture and high humidity). This in turn can result in a higher chance of return on investment by reducing DON/VOM levels, while protecting yield and test weight. When scab risk is low, the same benefits will likely not be observed. Secondly, scab fungicide applications can provide late-season flag leaf protection for foliar diseases. Usually under low scab risk environments, the risk for fungal leaf diseases is low (unless there are several mornings of prolonged dews to favor fungal infection), and a fungicide application at flowering will not contribute much to yield and test weight. Thirdly, the economic potential of a wheat crop under dry conditions can be low, so keep this in mind before making a fungicide application at flowering. In the table below, I provided some yield potentials and provided the estimated yield benefit of a scab fungicide under low disease environments. As you can see, the estimated yield benefit of flowering application under low disease environments will not offset cost of application. Although, this is from a relatively small data set, the message is that fungicides are best used to manage fungal diseases, which in turn can protect yield and test weight. Do not expect a fungicide to help a water-stressed wheat crop.

friskop.delrio

 

Andrew Friskop

Extension Plant Pathology, Cereal Crops

 

Joel Ransom

Extension Agronomist for Cereal Crops

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