Distinguishing Between Wheat Head Diseases and Disorders
Figure 1. Fusarium head blight (scab)
|Figure 2. Glume blotch (Photo credit: Dr. Gregory Shaner, Purdue University)|
Figure 3.(above) Black chaff
Figure 4.(below) Loose smut
June 6, 2008
|Figure 5. Common bunt|
|Figure 6. Ergots|
|Figure 7. Sooty mold|
Wheat is headed in most wheat growing parts of Nebraska. This article is a guide on how to distinguish between wheat head diseases and disorders.
Fusarium head blight (scab): One or more spikelets or the entire head is prematurely whitened or bleached (Figure 1). Partial bleaching of the wheat head is diagnostic of scab. Pink to salmon spore masses may appear on bleached heads. Bleached heads usually are visible over a wide area in the field. Wheat plants are of normal height.
Take-all: White heads occur in patches, often on plants that are stunted and have prematurely dead foliage.
Glume blotch: Discoloration on glumes appears dark to chocolate brown rather than white (Figure 2). Glume blotch can easily be confused with black chaff.
|Figure 8. Loose white heads (lower right) and loose smut|
Loose smut: Spikelets of infected heads are replaced by masses of olive-black spores (Figure 4). These spores may be blown off, leaving an empty rachis.
Common bunt (stinking smut): Glumes and awns spread apart, exposing bunt balls ("kernels" full of black spore masses). The bunt balls (Figure 5), which resemble kernels but are more rounded, remain on the head and give off a strong odor.
Ergots: Rare but can occur in Nebraska. Horn-shaped, purple-black ergots (Figure 6) replace individual grains on the head.
Sooty mold: A superficial gray-black fungal growth appears on the surface of the head (Figure 7).
Loose whiteheads: Caused by stem maggot injury; usually isolated and more conspicuous than heads bleached by diseases. The head and neck are whitened while the remainder of the plant is normal green (Figure 8). Pulling on the head causes it and the peduncle to easily detach from the stem.
Extension Plant Pathologist