Impact
Black chaff or bacterial blight is the most common disease in wheat and barley in the San Luis Valley. Xanthomonas translucens is the causal agent, attacking leaves, stems, and heads of barley and wheat.
Black chaff damage to the flag leaf and glumes limits the filling of the grains, resulting in lower bushel weight and yield. Black chaff is especially destructive when in the heads, potentially causing complete sterility.
Black chaff is common throughout the San Luis Valley. However, black chaff infections are more serious under center pivot irrigation.

Description and Symptoms

Leaves appear initially as water-soaked spots that elongate into streaks that may extend the full length of the leaf blade. These streaks become translucent and eventually turn tan or brown.

Under moist conditions, the bacteria may produce droplets that dry to a yellow, crystalline mass or that spread across the leaf surface, giving it a shellacked appearance when dry. This characteristic is an important difference between fungal and bacterial infections.

Infected heads may appear blackened, greasy and chlorotic plus some kernels may be shriveled.

Splashing water from rain or irrigation can spread the bacteria from diseased to healthy plants. Hail, wind, or other mechanical damage can increase infec- tions.

The bacteria have a high tolerance to temperature and moisture conditions and persists between seasons on infected seed, plant residues and some weedy grasses.

Integrated Management

Plant disease-free or the least infected seed available. Idaho research indicates bacterial levels in the seed can impact disease development. Levels can be tested in the laboratory.

No resistant commercial cultivars are presently available.

Avoid planting grain into infested stubble or weedy grasses. . No pesticides are currently available for black chaff control.

Avoid excessive and frequent irrigation, especially under sprinkler irrigation.

Reduce irrigation frequency as much as possible when infected plants are damaged from hail, wind or frost to reduce the potential incidence of infection.

Apply ample irrigation water to infected plants to minimize stress. However, foliage should become dry between irrigations to limit further disease development.

This material is based on work supported by the San Luis Valley Water Quality Demonstration Project Best Management Practices Advisory Committee, Colorado State University Cooperative Extension, Farm Service Agency, Natural Resources Conservation Service, and the U.S. Department of Agriculture under authorization as 1991 U.S. Department of Agriculture Water Quality Demonstration Project.