“Karnal bunt is not a major production or quality problem,” says Travis Miller, Texas Extension program leader for soil and crop sciences. “It is a major problem in selling wheat. Trading partners have quarantines against Karnal bunt infected wheat, and 80 percent of the Texas wheat crop goes out of ports (for export).”
Current infections in Throckmorton, Young, Archer and Baylor counties have cost Texas wheat farmers more than $27 million. “They can’t sell their wheat,” Miller said. More than 2.4 million bushels of wheat have been infected in those four counties.
Miller, during a grains seminar at the recent Blackland Income Growth Conference in Waco, said the disease spores could be widespread across Texas, “waiting for the right conditions. It’s probably been in the state at least 10 years, but last spring we had perfect weather for infection.”
Infection is not easy, Miller said. “The organism lies dormant until cool, wet weather stimulates germination. Spores, which may come in on seed, soil, plant parts, machinery or animal manure, may survive in the soil for five years and then break out.
“Spores enter the wheat plant ovary and mature as the seed matures. Infection occurs only during bloom,” Miller said.
The disease causes more problems than are warranted.
“We have a number of other bunts and smuts that cause more damage to production and quality than this one does,” Miller said. A telltale “fishy” smell makes infected wheat unmarketable.
The disease was first discovered in the Karnal region of India in 1931. From there it spread across India and Pakistan. It was identified in Mexico in 1970. The first incidence in the United States occurred in Arizona on Durum wheat in 1996. It was first detected in Texas in San Saba County in 1997 and no incidence was reported in the state from 1997 until 2001.
Wheat farmers’ best option is prevention, Miller said. The county quarantines are designed to contain the disease. In quarantined counties, the Animal and Plant Health Inspection Service (APHIS) imposes regulations on seed handling, grain handling, livestock feeding and equipment movement.
“Farmers may feed Karnal bunt infected wheat to livestock,” Miller said, “but the animals must be quarantined and fed oats or some other non-susceptible grain for five days prior to movement.”
Farmers in quarantined areas also must plant only spore negative, treated seed. Grain handlers must have seed tested and certified before moving it anywhere. “But buyers may still be reluctant to purchase from quarantined areas,” Miller said.
Some infected wheat has been disposed of in landfills.
“It’s also possible to treat infected grain with a steam process and then feed to livestock.”
Miller recommends growers exercise caution in buying planting seed. “Know where it comes from and make certain it’s high quality. Use a systemic seed treatment at the upper end of labeled rates, and good coverage is critical.” Seed treatments include Vitavax and PCNB. “This is not a stand-alone practice to control the problem,” Miller said. Foliar fungicides also may hold promise for in-season treatment.
Cleaning equipment provides another important safeguard. “Equipment carries soil and plant parts from an infected field into a clean one,” Miler said. “High temperatures and chlorine bleach can sterilize Karnal bunt.”
The best option may be a few years away. “Overall, the best control strategy will be resistant varieties,’ Miller said. “Currently, we have no resistance in Texas, although several crosses with resistance have been identified. Currently, we have no real test sites in the Southwest. A Karnal bunt working group has begun to seek research funds to study the problem.”