Distinguishing Between Wheat Head Diseases and Disorders

Distinguishing Between Wheat Head Diseases and Disorders

picture of fusarium head blight picture of glume blotch

Figure 1. Fusarium head blight (scab)

Figure 2. Glume blotch (Photo credit: Dr. Gregory Shaner, Purdue University)
picture of black chaff  

Figure 3.(above) Black chaff

Figure 4.(below) Loose smut

 
picture of loose smut  

June 6, 2008

Photo of Common Bunt
Figure 5. Common bunt
photo of Ergots
Figure 6. Ergots
Photo of Sooty mold
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.

Photo ofLoose white heads and loose smut
Figure 8. Loose white heads (lower right) and loose smut
Black chaff: Brown-black, water-soaked and necrotic streaks cause darkening on glumes (Figure 3). Streaking also can occur on leaves. During humid weather, a cream to yellow ooze appears on infected plant parts. Bands of healthy and necrotic tissue appear on awns.

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.

Stephen Wegulo
Extension Plant Pathologist