Herbicide and Nonherbicide Injury Symptoms on Spring Wheat and Barley

Common Root Rot (Fusarium & Helminthosporium spp.)
Common root rot is difficult to diagnose and often goes unnoticed. This disease enters plants through the root causing seedling blight or attacks older plants predisposed to several environmental stresses. Seedlings can be killed before or after emergence. Infected plants occur in random patches in fields and are stunted and lighter green than healthy plants. Older plants that are infected will mature early, produce few tillers, have shriveled seed or no seed, and produce heads that are bronzed, bleached, or white. Upon close examination, infected root systems will display a brown color and have fewer roots than healthy plants. Plants infected at the culm base can lodge. See photos 32 and 33.

Photo 32 Wheat plants attacked by common root rot turn prematurely and appear white. The heads of these grain plants are empty. Green plants in foreground are healthy.

Photo 33 Plants affected by common root rot (left) show a poorly developed root system compared to healthy plants on the right.

Septoria Leaf Blotch (Septoria spp.)
Septoria leaf blotch is particularly damaging to wheat but rarely causes significant losses in barley. Several Septoria species attack all aerial plant parts of wheat and barley throughout the growing season. Initial symptoms of this disease are chlorotic flecks that usually begin on the lowest leaves of healthy plants. Lesions appearing lens-shaped are caused by Septoria nodorum whereas lesions that show parallel borders are caused by Septoria tritici. When no leaf moisture is present, infection sites quickly dry out and develop yellow margins that later turn red brown. Older lesions will develop ashen gray centers with small black specks, which are the pycnidia. The pycnidia harbor spores that disperse with splashing raindrops spreading the disease to healthy plant tissue. These black specks are visible to the eye and serve as a good diagnostic tool. See photo 34.

Photo 34 Lesions caused by Septoria tritici show black pycnidia in centers that can be seen without the use of a hand lens

Tan Spot (Pyrenophora trichostoma)
Spring wheat is susceptible to tan spot while barley is a poor host. Tan spot develops initially as yellow-tan flecks on both upper and lower leaf surfaces. The lesions expand into lens-shaped tan blotches with yellow borders. A characteristic of tan spot is a small, dark brown center. Lesions may coalesce and form larger ones. Injury from this disease can be confused with injuries caused by herbicides in the bipyridylium and benzonitrile families, and also difenzoquat (Avenge) and propanil (Stampede). See photo 35.

Photo 35 Yellow borders with small dark-brown centers are the typical symptoms of tan spot.

Produced by Communication and Educational Technology Services, University of Minnesota Extension.

In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request. Please contact your University of Minnesota Extension office or the Extension Store at (800) 876-8636.

University of Minnesota Extension is committed to the policy that all persons shall have equal access to its programs, facilities, and employment without regard to race, color, creed, religion, national origin, sex, age, marital status, disability, public assistance status, veteran status, or sexual orientation.