Look Out for Wheat Diseases

With recent rainfall events across Nebraska, producers must remain vigilant against wheat diseases. Last week, extension plant pathologist Stephen Wegulo and I scouted some fields in Johnson and Pawnee Counties where we observed diseases such as stripe rust and fungal leaf spot in wheat.

According to the CropWatch article published on May 10 on wheat disease update, stripe rust has been confirmed in eight counties in southern NE, including Saline, Jefferson, Gage, Lancaster, and Pawnee. You can visit cropwatch.unl.edu to stay updated on the wheat diseases in Nebraska.

Signs & Symptoms of some of these diseases

Stripe rust manifests as yellow to light orange pustules arranged in a distinct linear "stripe" fashion on the leaf. It is a foliar fungal disease favored by cool night temperatures and wet field conditions. In severe conditions, pustules may develop on the glumes and awns.

Septoria tritici blotch and tan spot are two important fungal leaf spot diseases. Tan spot lesions appear as small patches ranging from tan to brown, gradually enlarging into oval or lens-like shapes. They are accompanied by a yellowish or chlorotic ring around their edges and contain a dark speck at their center. Whereas plants affected with septoria appear to have elliptical, tan-brown lesions with a yellow halo developing on the leaves; the center of the lesion dies, appearing gray brown in color, giving the lesion a speckled appearance.

Another economically significant wheat disease to look out for is fusarium head blight (FHB). It can cause yield loss as high as 50%. Wheat spikelets infected with FHB become bleached, and the disease spreads upward and downward by sequentially infecting the spikelets. Pink or orange spore masses can also be observed on infected spikelets, particularly at the base. Infected kernels become shriveled, chalky, and discolored white-pink. Infected kernels are highly contaminated with mycotoxins which reduces their quality and market value.

Management strategies

It is crucial to scout your field to determine which diseases are affecting the plants and the severity of the infection before deciding to apply a fungicide. Stripe rust and fungal leaf spot diseases are managed by planting resistant varieties and applying fungicide to susceptible varieties timed to protect the flag leaf. Flag leaf is the last leaf of wheat plant and accounts for over 50% of the photosynthates used for grain development. Therefore, it is important to protect flag leaf from disease or insect damage to ensure plant’s full yield potential. For FHB, application is recommended when favorable conditions exist prior to and throughout heading. The best application timing is early flowering, but application up to 7 days after initiation of flowering can reduce FHB and mycotoxins throughout heading. There is a list developed by the North Central Regional Committee on Management of Small Grain Diseases on efficacy of fungicides for wheat disease control based on appropriate application timing. You can access this list at extension.unl.edu/nemaha/ag-resources/

You can contact your local extension office for more information on wheat disease management or reach out to me at rlamichhane3@unl.edu or 402-274-4755 if you have any questions.

Ritika Lamichhane
Extension Educator
Nemaha County
May 2024