Source: Erick DeWolf, Research and Extension Plant Pathology, Kansas State University

The wheat crop is fast approaching growth stages where fungicide should be applied. Many growers are asking about the potential need for fungicides this year. We have been conducting fungicides evaluations for the past three years in multiple locations in Kansas. Our goals are to (1) help growers evaluate which varieties are most likely to give a favorable yield response to fungicides, and (2) identify situations when these products are most likely to result in a yield response great enough to justify the applications.

The locations in 2008-2010 included Sumner, Reno, and Republic counties. The treatments included comparisons of fungicide treated and untreated plots of 10 wheat varieties with different levels of genetic resistance to multiple diseases.

Which wheat varieties are most likely to give a profitable yield response to foliar fungicides?

The wheat varieties in this study were divided into two groups based on their susceptibility to some of the most common leaf diseases in Kansas. The group with multiple susceptibilities included Jagger, Jagalene, 2137, Overley, PostRock and Fuller. The group of varieties that currently has higher levels of resistance to these same diseases includes Everest, Armour, SantaFe, and Karl 92.

The results of this study indicate that the average yield response of the varieties with multiple susceptibilities was at least double that of the more resistant varieties (Figure 1). The chance of a yield response of at least 4 bu/acre (a yield response that is comparable to the average yield response in Kansas, and which results in a reasonable profit for the grower) was much greater when applying fungicides to the varieties with multiple disease vulnerabilities than those with higher levels of resistance (Figure 2). 

Evaluating the Need for Fungicides in Wheat

Evaluating the Need for Fungicides in Wheat

Can scouting for disease improve my chances of seeing a yield increase when using fungicide applications?

The results of this study indicate that taking the time to scout for disease can greatly increase chances of correctly identifying situations when it is beneficial to use fungicides in wheat. For example, the average yield response to a fungicide applied to a susceptible variety when the disease is present on the upper leaves at heading was more than 7 bu/acre (Figure 3). The average yield response for the same variety when no disease is observed at heading is about 1.5 bu/acre. The average yield response when spraying a variety with higher levels of genetic resistance is about 0.3 bu/acre. The same patterns carry through when we consider the chances of seeing a 4 bu/a yield response (Figure 4).

Evaluating the Need for Fungicides in Wheat

Evaluating the Need for Fungicides in Wheat

The higher prices of grain and lower cost of some fungicide products make even small yield improvement a reasonable investment. Growers can use the average yield responses from this study to help evaluate how aggressive they want to be with fungicides this year.

Key concepts for profitable use of fungicides: 

  • Wheat varieties that are susceptible to the most common leaf diseases are more likely to give and larger and more consistent yield response to foliar fungicides than varieties with resistance to these diseases. 
  • Paying attention to the regional risk of disease and scouting your fields greatly increases your chances of identifing years where fungicides result in the largest yield responses.

The current risk of disease is low in most areas of the state. There have been a few reports of low levels of leaf rust and powdery mildew in central Kansas, suggesting some fields might be at a moderate risk of disease. The dry weather is probably slowing the spread of disease. The lower cost of fungicides and the higher grain prices may still justify treatment.