Use of Fungicide Seed Treatments to Improve Wheat Health - UNL CropWatch, Aug. 30, 2012

Use of Fungicide Seed Treatments to Improve Wheat Health - UNL CropWatch, Aug. 30, 2012

 Common bunt of wheat  Loose smut of wheat
 Figure 1. Common bunt (stinking smut).  Figure 2. Loose smut.

August 30, 2012

Fusarium head blight

Figure 3. Kernels damaged by the Fusarium head blight fungus.

Black point of wheat

Figure 4. Black point.

Ergot-contaminted wheat

Figure 5. Ergot-contaminated grain.

Using seed treatments for winter wheat can help you manage the disease threat and optimize yield potential for next year’s crop. While there may be a higher initial cost for using clean/certified, treated seed, the cost is almost always exceeded by the benefit in yield.

Several wheat diseases are caused by fungal pathogens that are soilborne and/or seedborne.

  • Soilborne pathogens include those that cause root and crown rots and seedling blights, such as Bipolaris, Fusarium, Pythium, and Rhizoctonia.
  • Seedborne pathogens are associated with head diseases that affect the grain. These diseases include common bunt (also known as stinking smut, Figure 1), loose smut (Figure 2), Fusarium head blight (Figure 3), black point (Figure 4) and ergot (Figure 5).

Economic Importance of Soil- and Seedborne Diseases

Soil- and seedborne diseases reduce yields as well as grain quality. Grain contaminated by common bunt can be rejected at the elevator, often resulting in total loss. Although loose smut does not affect grain quality, yield losses of up to 40% can result from the disease.

Incidence of ergot in wheat is relatively low; however, in 2011 favorable environmental conditions (cool, wet weather during flowering) resulted in epidemic levels of the disease in several wheat fields in south central and southeast Nebraska. Sclerotia or ergots (compact masses of the ergot fungus) can lower grain quality. In addition, the ergots contain toxic alkaloids that can cause ergotism and death in humans and livestock.

Fusarium head blight can cause significant losses resulting from floret sterility, poor grain fill, and contamination of grain by mycotoxins. If seed contaminated with the Fusararium head blight fungus is sown, seedling emergence can be reduced by up to 80%.

Black point can significantly reduce the bread-making quality of wheat. Heavy contamination of grain with black point can result in discolored flour. This can be a cause for rejection of the grain by millers. If grain affected by black point is sown, the causal fungi which include Bipolaris and Alternaria can cause seedling blights and root rots, resulting in poor stand establishment.

Effect of Drought on Soil- and Seedborne Pathogens

Soil- and seedborne pathogens can survive adverse environmental conditions such as drought and winter temperatures by becoming dormant or forming survival structures. Additionally, seedborne pathogens are protected by the seed and/or the environment in which the seed is stored. When favorable environmental conditions (moisture and ambient temperatures) return, the pathogens become active again. The drought of 2012 will not reduce the risk posed by soil- and seedborne pathogens. Management measures against these pathogens should be taken as they would in a normal year.

Management of Soil- and Seedborne Diseases

Four strategies can be used in combination to manage soil- and seedborne diseases of wheat:

  1. seed treatments,
  2. cleaned seed,
  3. resistant varieties, and
  4. crop rotation.

Seed treatments are important for several reasons:

  • They control seed-transmitted pathogens that may be surface-borne on the seed or internally seedborne. In addition, they control soilborne pathogens such as Bipolaris, Fusarium, Pythium, and Rhizoctonia that cause root and crown rots and seedling damping off and blights. Systemic seed treatments also provide additional protection against fall foliar diseases.
  • In addition to controlling diseases, fungicide-insecticide combination seed treatments control insect pests such as wireworms, Hessian fly, and fall season aphids.
  • By controlling seedling damping off, seed treatments improve stand establishment and result in healthy, vigorous seedlings.

It is preferable to buy certified treated seed or have it cleaned and treated by a commercial seed conditioner. If seed is treated on-farm, it is essential to clean it before treating. Cleaning seed before treating is especially necessary if the seed-transmitted diseases listed above were present in the field during the growing season.

For the seed treatment to be effective, ensure thorough, uniform coverage. If possible, use a broad spectrum systemic fungicide or fungicide-insecticide combination product. For a list of seed treatment fungicides for control of soil- and seedborne diseases of wheat, see the table of Wheat Seed Treatment Fungicides from the UNL 2012 Guide for Weed Management with Insecticide and Fungicide Information. A more comprehensive list of seed treatment products for control of diseases and insect pests of wheat can be found at the Nebraska Department of Agriculture Pesticide Registrations website. 

For more information on diseases affecting grain and seed quality in wheat, see Fungal Diseases Affectng Grain and Seed Quality in Wheat (EC1874).

Resistant varieties can be used in combination with seed cleaning and seed treatments to more effectively manage soil- and seedborne diseases of wheat.

Importance of Using Clean/Certified, Treated Seed

The importance of using clean/certified, treated seed cannot be overemphasized. Clean/certified, treated seed optimizes the chances of obtaining high yields. Using farmer-saved or bin-run seed is likely to result in poor variety purity, a low germination percentage, poor stand establishment, and disease, insect, and weed problems. The result will be reduced yield and poor grain quality. Total loss may result if grain is heavily contaminated with fungal spores. Additional costs may be incurred in treating for diseases, insects, and weeds resulting from use of poor quality seed. In terms of dollars, the return from using clean/certified, treated seed will almost always exceed the cost of the seed. Using clean/certified, treated seed is a form of insurance that is definitely worth the cost.

Stephen Wegulo
Extension Plant Pathologist