Fungicide on Wheat: To Spray or Not to Spray ?

This year wheat growers have and are asking if an early (4 to 5 leaf growth stage) and/or late (early flower) fungicide application should be made. Early-season disease (aka: tan spot) is showing up in locations that have had several days of rain (Figure 1). Risks of a tan spot epidemic increase with:

• cloudy, rainy weather
• growing a susceptible wheat variety
• planting into last year’s wheat residue or stubble

Time marches on and many producers have long since made the first fungicide application decision. In general, tan spot disease pressure has been low in the RRV and fungicide application has not been recommended.
The following information addresses the next fungicide application decision that must be made shortly in southern locations and on winter wheat.
Does fungicide application really preserve wheat grain yield and kernel quality?

During 2004 and 2005, on-farm disease management trials of wheat were conducted in Otter Tail, Red Lake, Norman, Roseau, and Kittson Counties. Various disease management strategies were tested on five wheat varieties in both years. Results showed that varieties with resistance to FHB (Alsen, Knudson, Walworth) yielded significantly greater than susceptible varieties (Oxen, Reeder) when a fungicide application was not made. However, when a fungicide treatment was applied, the yields of susceptible varieties improved substantially and differences were no longer significant.

While Oxen and Reeder yields increased with fungicide application, quality characteristics such as test weight; damaged and shrunken kernels; and deoxynivalenol (DON, vom) remained substantially higher (damaged kernels and DON) or lower (test weight) than those of resistant varieties. Resistant varieties had higher quality kernels compared to susceptible varieties irrespective of fungicide application.

Are all wheat varieties created equal (economically speaking of course)?
Without a fungicide application, varieties with FHB resistance resulted in significantly greater estimated $/A than susceptible varieties. Similar to yield results, if a fungicide application was made, returns were not significantly different between the two resistance groups.

What happened last year ?

During 2006, 12 wheat varieties were tested at two on-farm disease management trials sites (Wilkin and Red Lake Counties). Disease was not a yield-limiting factor last year. In fact, most fields needed repeated applications of rain, rather than fungicide.

Yields and estimated returns/A were not significantly different between varieties. When yields of the no fungicide control and fungicide application at early flower (4 fl. oz./A Folicur, active ingredient tebuconazole) are compared, a trend for a slight increase in yield exists after treatment with fungicide (Figure 1). However, the additional costs incurred for fungicide and application were not recovered. Negative returns resulted from fungicide application in over half the varieties (Table 1). An application of fungicide on Ulen, Walworth, Steele-ND, Freyr and Oklee resulted in positive returns.
A wheat crop still has the ability to offer a positive economic outcome if input costs can be controlled. If disease doesn’t appear to be a limiting factor for this year’s crop, a fungicide application will not result in a positive economic return.

Charla Hollingsworth, Plant Pathologist
and
Doug Holen, Regional Educator - Crops