Karnal bunt, a fungal disease of wheat, has been identified in at least five north Texas counties, and Texas Department of Agriculture and USDA officials are testing surrounding areas to determine if it has spread.

Three counties, Throckmorton, Archer and Young, have been quarantined, an action “necessary to prevent spread of the disease and to protect the other wheat producing areas of Texas,” said Texas Agriculture Commissioner Susan Combs. “The quarantine also will be a key in preventing infected wheat from entering the export market.”

Baylor County is under temporary regulation. San Saba County has been under a Karnal bunt quarantine since 1997 and fields showed significant infestation this year.

In late June, surveys indicated 1.3 million bushels of wheat had been infected by Karnal bunt, according to TDA spokesperson Beverly Boyd.

Quarantines remain in effect for five years if the area stays free of the fungus. If it reappears within the five-year period, the clock starts over.

In a report to farmers and wheat industry observers, Travis Miller, Texas A&M Extension specialist for small grains, explained how the quarantines work.

“In addition to quarantining fields that tested positive, regulated status requires that all elevators be tested for presence of the disease; all wheat harvested must be checked for presence of the disease before hauling to an elevator or out of the county; hauling wheat or triticale hay from the regulated area is prohibited; all harvest and tillage equipment is subjected to steam cleaning prior to movement from the regulated area.

“Also, other restrictions designed to reduce the possibility of spreading the disease to other locations or into commerce may be imposed. Wheat that tests positive must be heat treated to kill the organism before it can be used.”

Boyd said a quarantine affects the entire county. “Every wheat farmer, whether his fields tested positive or not, must have his wheat tested and certified before he can move the crop out of the county. If tests are negative, he has no problems.”

Positive tests require heat treatment or other action to control the fungus.

Miller said Karnal bunt does relatively little crop damage compared to diseases common to Texas or to other common smuts and bunts. The problem, however, comes from the fishy smell the disease causes, making it unacceptable for export markets.

“In addition to locating infected fields, TDA is trying to find markets for affected grain,” Boyd said.

Miller said the pathogen generally enters a field on infested wheat seed, plant parts, livestock, manure or infested soil carried on agricultural equipment. “Spores can move in the wind, but are relatively heavy and are not believed to be carried long distances,” he said.

Spores may lie in the soil until conditions become favorable for germination.

“During cool, wet weather, the teliospores near the soil surface can germinate and produce a new set of airborne spores called primary sporidia. If primary sporidia production occurs while the wheat is flowering, the fungus can infest the ovary in the wheat flower.

“If the wheat is not flowering during primary sporidia release, sporidia can produce secondary sporidia, which give the fungus another opportunity to attack the wheat flowers.

“As the kernel matures it becomes blackened with a mass of teliospores and damaged by concurrent bunting or eroding of the embryo end of the kernel.”

Miller says a level as high as 1 percent bunted kernels in any field is “quite unusual.”

Boyd said the areas where investigators have found Karnal bunt this spring may have harbored the fungus for several years. “Farmers in those areas generally graze their wheat and do not harvest the grain,” she said. This year, conditions were favorable for grain production and more farmers decided to harvest.

Those conditions, plenty of spring moisture, also favored development of the disease.


e-mail: ron_smith@intertec.com