Figure 1. Leaf rust on a wheat leaf.	Figure 2. Tan spot on a wheat leaf.

Managing Wheat Diseases for Higher Yields

For purposes of choosing or deciding which management measures to apply, wheat diseases common to Nebraska can be classified into three major groups: fungal, bacterial, and viral.

(Above) Figure 3. Fusarium head blight in an irrigated wheat field. (Inset) Fusarium head blight on a wheat head. (Right) Figure 4. Black chaff on wheat heads. (Below) Figure 5. Wheat plants showing severe symptoms (yellowing and stunting) of wheat streak mosaic. (Inset) Wheat streak mosaic symptoms on a wheat leaf.

• Fungal. Fungal diseases that occur in Nebraska include the rusts (Figure 1), leaf spots (Figure 2), bunts/smuts, Fusarium head blight (scab, Figure 3), seedling blights, and crown and root rots.

• Bacterial. Black chaff, (Figure 4) also known as bacterial stripe or bacterial leaf streak when leaves are affected, is the only bacterial disease of wheat observed in Nebraska.

• Viral. The most important viral disease in Nebraska is wheat streak mosaic (Figure 5). Other viral diseases include barley yellow dwarf and soil-borne mosaic.

Several strategies can be used to manage fungal diseases of wheat.

• Start scouting fields early in the growing season.

• Monitor the weather when determining whether a treatment will be beneficial. Most fungal diseases of wheat are favored by wet weather.

• Keep an eye on rust development in southern states. Rusts overwinter in the warmer southern states and are blown north during spring. Knowing the status of rust diseases south of Nebraska can help prepare you to take timely management measures.
• Plant wheat varieties adapted to your area and plant at the recommended date for your area. Nebraska has a wide variation in climate and variety selection can help ensure a vigorous, healthy crop that is less vulnerable to diseases. Plant resistant/tolerant varieties and avoid varieties known to be highly susceptible to diseases.

Consider a Fungicide

When conditions favor development of foliar fungal diseases, a fungicide application often may be necessary. All the fungicides used to control foliar fungal diseases in Nebraska are very effective; however, some are more efficacious than others on specific diseases.

To maximize the return on a fungicide application, use the fungicide that is least expensive and most efficacious on the target disease. Foliar fungicide applications on wheat are most profitable if timed to protect the flag leaf. In cases where disease pressure is high early in the growing season, it may be necessary to apply a fungicide before flag leaf emergence for early season disease suppression.

The decision to apply a foliar fungicide depends on several factors, including:

• favorability of the environment to disease development,
• susceptibility of the variety planted to disease,
• fungicide application cost,
• yield saved due to fungicide application, and
• the price of wheat.

Management strategies for Fusarium head blight (scab) include applying an appropriate fungicide during early flowering, managing irrigation, avoiding planting wheat into corn stubble, and planting tolerant varieties. The bunts/smuts, seedling blights, and crown and root rots are effectively controlled with fungicide seed treatments. To maximize yields, it is recommended that certified, fungicide-treated seed be planted every year.

Managing Bacterial Diseases

Black chaff can be managed by

• planting certified, pathogen-free seed,
• managing irrigation to allow foliage to dry between irrigations, and
• avoiding varieties known to be highly susceptible.

Managing Viral Diseases

Viral diseases can be managed with a combination of cultural practices and selection of resistant/tolerant varieties. Recommended strategies for controlling wheat streak mosaic include:

• controlling volunteer wheat, the most important strategy. All volunteer wheat should be dead at least two weeks before fall planting.
• planting on the recommended date for your area (avoid early planting),
• planting tolerant varieties,
• controlling post-harvest weeds, and
• avoiding curl mite-virus host crops growing after wheat emergence.

Incidence of barley yellow dwarf virus can be reduced and yield loss minimized by controlling aphids; however, this may not be economical as the disease may be spread by aphids that escape treatment or migrate from non-treated areas. Barley yellow dwarf can be more effectively managed by planting on the recommended date for your area (avoid early planting), planting resistant/tolerant varieties, and controlling grassy weeds.

The primary management strategy for soil-borne mosaic virus is planting resistant varieties. Avoiding early planting also can help reduce damage caused by the virus.

Stephen Wegulo
Extension Plant Pathologist, Lincoln

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