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16
Feb
2017
Wheat disease update: Stripe rust confirmed in seven counties
Author: Jason Kelley, Wheat & Feed Grains Extension Agronomist

By Jason Kelley, Extension Wheat and Feed Grains Agronomist and Terry Spurlock, Extension Plant Pathologist

With the warm temperatures this winter and relatively little cold weather, it is not surprising that foliar diseases are being found.  As of today, stripe rust has been confirmed in seven counties across eastern Arkansas (see map below), but is likely more widespread than the confirmed areas.   Stripe rust has been found this early in past years, so this is not all that unusual, but still is a concern for producers.  Even though wheat varieties may be rated as resistant to stripe rust, it can still be found on those varieties at the current growth stages.  The wheat resistance genes to stripe rust become expressed closer to heading (known as adult plant resistance), so a variety that has stripe rust now may be resistant in the end.  The concern is that stripe rust strains can change and a resistant variety last year may not be resistant this year.  If stripe rust is found now (especially on a known susceptible variety), it can be easily and economically controlled with propiconazole or tebuconazole foliar fungicides which can be tank-mixed with planned herbicide applications.  A fungicide application now will not last season long, but will control stripe rust to preserve yield, limit spread of spores to other fields and allow time to see if the resistance genes kick in.  If the variety is truly susceptible, another fungicide application will be needed near heading to protect yield.  Current wheat variety disease ratings can be found at: http://www.uaex.edu/farm-ranch/crops-commercial-horticulture/wheat/2016%20Wheat%20Update%20Final.pdf 

Figure 1. (Left) Wheat stripe rust distribution in AR as of 2-16; Figure 2. (Right) Stripe rust pustules on blade of wheat

Leaf rust and other foliar disease:

There are other foliar diseases that that are showing up in addition to stripe rust.  Last week leaf rust was at trace to low levels around the state and septoria tritici blotch and powdery mildew could also be found at low levels in some wheat fields.  Fungicide applications for these diseases are not recommended at this time.  Typically optimal fungicide application timing for control of foliar disease occurs when the flag leaf emerges (Feekes 8).

Figure 3. (Left) Leaf rust on cereal rye cover crop; Figure 4. (Right) Powdery mildew low in canopy


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