NEWS for North Dakotans
Agriculture Communication, North Dakota State University
7 Morrill Hall, Fargo, ND 58105-5665
January 20, 2000
Loose smut, a seed-borne fungal disease, was a problem for some North Dakota wheat and barley producers last year. For wheat, loose smut was most common in the state's western crop reporting districts, with between 18 percent and 40 percent of headed fields displaying masses of black smut spores where kernels of wheat should have been, says a specialist with the North Dakota State University Extension Service.
"What the incidence of loose smut tells me is that growers were interested in reducing their input costs, and so they reduced their use of seed treatment," says Marcia McMullen, extension plant pathologist at NDSU. "This is unfortunate because loose smut can be controlled very effectively in both wheat and barley, and there are several products available."
In barley, loose smut was most common in North Dakota's south central, southeast and west central crop reporting districts, where between 60 percent and 77 percent of headed fields showed symptoms. Overall, the severity of loose smut in the state's wheat fields averaged between 2 percent and 3 percent of tillers infected within a field. For barley, severity averaged between 2 percent and 4 percent of tillers infected. The disease does not pose any health risks to humans or animals.
Only systemic fungicides containing the active ingredients carboxin, difenoconazole, tebuconazole or triadimenol will control the disease in wheat. Difenoconazole is not effective in controlling the disease in barley, McMullen says. The cost for seed treatments range from about $1 to $1.50 per bushel for both wheat and barley, depending upon which product growers use.
Loose smut infects the seed of both wheat and barley internally, in the embryo, but the loose smut pathogen for wheat does not infect barley, and vice versa, McMullen says. The percentage of infected seeds producers plant will correlate closely to the percentage of yield loss they will experience, so it's important for producers to obtain loose-smut-free seed or use seed treatment. Organic producers must control this disease by obtaining loose smut-free seed.
"There is no visible sign of infection in the seed. It appears normal in terms of color and shape," McMullen says.
Infections of wheat and barley plants occur during flowering and heading. McMullen says the smutty heads seem to develop sooner than uninfected heads, so the spores are usually available for the wind to transport to healthy heads, where the spores germinate and move into the embryo. The fungus then develops along with the planted seed's growing point in the spring and summer, and at heading, the fungus spores replace the kernels.
The North Dakota State Seed Department offers a loose smut embryo test for barley but not for wheat, because test results have proven unreliable for wheat, McMullen says. Infection levels of about 2 percent or more in barley represent the economic threshold for seed treatment. For wheat, she suggests that producers base their decision to treat on whether loose smut was present in their fields last year. In short, if loose smut was present, use a seed treatment on wheat--especially on saved seed.
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Source: Marcia McMullen (701) 231-7627
Editor: Dean Hulse (701) 231-6136