Call it a fluke or not, this year's Karnal bunt outbreak that infected more than 2 million bushels of Texas wheat in six counties has left farmers with only one real solution to avoid the fungus in future crops.
"There's only one step that we know for absolute certain that will prevent infestation, and that is to not plant wheat, or plant a non-host alternative crop," said Dr. Travis Miller, associate head and Texas Cooperative Extension program leader for the department of soil and crop sciences at Texas A&M University.
Karnal bunt is a fungal disease of wheat, durum wheat and triticale. The fungus typically affects a portion of the kernel, leaving an eroded or "bunted" area on the kernel and a mass of black spores which produce an offensive, fish smelling odor. It thrives under moist, cool conditions like those experienced in Texas this past spring.
Karnal bunt has cost the Rolling Plains economy more than $27 million this year, according to an economic analysis by Stan Bevers, an Extension economist at Vernon. The economic analysis outlined the projected impact of Karnal bunt on a four-county area economy that included Young, Archer, Throckmorton, and Baylor counties.
"Approximately 2.8 million bushels of Rolling Plains winter wheat was classified as 'bunted' after samples tested positive at federal laboratories," Bevers said. "Another seven million bushels tested negative as bunted wheat, but, because it was grown or co-mingled with wheat grown in an infected area, it cannot be marketed through normal channels."
Miller said there are several methods to minimize the risk of Karnal bunt. These include verifying planting seed is free of disease, as well as making certain farm equipment entering fields is free of disease. Many farm groups and scientists are calling for a step up in research to combat the disease that is known to have been in the U.S. since 1996 and in Asia since 1931.
"This karnal bunt originally was a native to quite a number of countries, especially Mexico, for more than 30 years," said Dr. Norman Borlaug, a Nobel Laureate at Texas A&M.
Borlaug, who won the Nobel Peace Prize in 1970 for developing broadly adapted high-yielding rust-resistant wheat varieties and integrated improved crop management practices to help feed the hungry in Third World countries, said future breeding programs "should incorporate genes for resistance to Karnal bunt into winter wheats found in the western part of the U.S."
"Since it is a new disease in a country, there is always a fear that when you may have ideal weather conditions, like we had this past spring, infections might be worse. The best thing to do is to develop and incorporate genetic resistance into the varieties," Borlaug said.
When Karnal bunt is found in a crop and a specific location of field is not identified, a quarantine restricting grain and equipment movement is imposed for that county. Grain must have a phytosanitary certificate to move out of a quarantined, or regulated area.
"When we first got Karnal bunt, they just more or less shut us plumb down," said Chuck Meyers of Seymour, who runs Meyers Grain. "We couldn't trade any grain. It was just, more or less, for two-and-a-half or three months no activity. Period."
For Karnal bunt to have a presence in wheat crops, it must have moist conditions and cool temperatures during the bloom period.
"You have to have very special conditions to get an epidemic of any proportion," Borlaug said. And there were ideal conditions for Karnal bunt resulting in infestations in six counties this past year--San Saba, Throckmorton, McCullough, Young, Baylor and Archer.
"The fact that it is widescale indicates we have had the presence of this disease in Texas for many years," Miller said. "It appears that we can go years without any infection, but under special weather conditions like we had this year, we may well have another flare-up."
In 1996, two counties were suspected where durum wheat seed was planted and found infected--El Paso and Hudspeth counties were quarantined because growers were known to have planted infected durum wheat seed. In 1997, extensive testing in the state began for the first time and Karnal bunt was found in hard red winter wheat in San Saba county where 19 fields were infected, Miller said.
"That began a series of routine testing for several years, but no more Karnal bunt was found until this year," he said.
Spores can live in the soil five years or more until conditions favor growth, usually a period of cool, wet weather in the spring when wheat is blooming. A fungal mat grows on the surface of the soil, and this growth sheds secondary spores. Miller said if these spores are released during the flowering stage of wheat and come in contact with the wheat ovary, bunted kernels are produced.
"There's a number of procedures a farmer can do to minimize his risk and go ahead and plant wheat," he said. "The first thing is to select high quality planting seed known to be free of disease--the No. 1 source of the infection is infected planting seed, so buy certified seed known to be free of disease. Second, use effective seed treatment ... I say effective, we have to use that with a little bit of grain of salt because we know none of the seed treatments are 100% totally effective on this disease. You might get up to 75% control of disease if we use effective seed treatment."
Miller also suggested watching movements of soil and plant parts.
"When equipment comes into your field, make sure it hasn't come from an infected field, or that it has been thoroughly cleaned prior to entering your field," he said.
For more information about Karnal bunt, visit http://soil-testing.tamu.edu/publications/872792-karnalbunt.pdf .