Figures 1 and 2. Seed-transmitted diseases affecting this year's wheat crop include loose smut (left), common bunt or stinking smut (above). A rainy June contributed to increased disease incidence across much of the state's wheat-growing area this year.

August 28, 2009

Figure 3. Black point of wheat.

(Left) Figure 4. Fusarium head blight. Figure 5. Black chaff

Figure 6. Scabby wheat grain.

Wet weather during June favored development of many wheat diseases. Notable among them were seed-transmitted diseases. These diseases lower both yield and grain quality and some can cause up to 100% economic loss the following year due to rejection of contaminated grain at the elevator. Several seed-transmitted diseases can cause damping off and seedling blights during or after emergence in the fall. Damping off and seedling blights also can be caused by fungi that are not seed-transmitted but live in the soil.

The Diseases

Seed-transmitted diseases include loose smut (Figure 1), common bunt or stinking smut (Figure 2), and seedling blights resulting from seed infected by fungi that cause black point (Figure 3) and Fusarium head blight or scab (Figures 4 and 6). Seed also can harbor fungi that cause tan spot and Septoria leaf and glume blotches, which increases inoculum for these diseases. Black chaff (Figure 5), a bacterial disease, also is seed-transmitted. However, fungicide seed treatments do not control black chaff. For information on how to manage black chaff, see NebGuide G1672, Black Chaff of Wheat.

Why It Is Important To Treat Seed

Fungicide seed treatments control seed-transmitted diseases caused by fungi and soilborne fungi that cause damping off and root and crown rots. Seed treatment is a key factor in establishing a healthy and vigorous stand, which optimizes the chances of obtaining high yields. If systemic fungicides are used to treat seed, additional protection from fall season foliar diseases is provided. It is important to note that treating seed infected by the Fusarium head blight (scab) fungus controls damping off and seedling blights in the fall, but will have no effect on development of scab the following growing season. For information on how to manage scab, see Extension Circular EC1896, Fusarium Head Blight of Wheat.

Treating Seed

It is best to buy certified treated seed or use a commercial seed conditioner to clean and treat seed. If you plan to treat it on-farm, have it cleaned first. Thorough fungicide coverage maximizes effectiveness of the seed treatment. For a partial list of seed treatment fungicides for control of residue-borne, soilborne, and seedborne diseases, see NebGuide G1671, Management of Residue-Borne Diseases of Wheat.

Due to the many seed-transmitted diseases that affected wheat grain this year, including loose smut, common bunt, scab, and black point, it is highly recommended that certified, fungicide- treated seed be planted for next season’s crop. If farmer-saved or bin-run seed must be used, it should be cleaned thoroughly and treated with a systemic fungicide before planting.

Stephen Wegulo
Extension Plant Pathologist