Alfalfa grower Rich Callahan doesn't want to share any of his yield with stem nematodes. “We try to do the things that will keep the pests under control,” says Callahan, of Royal City, WA.
That includes planting high-quality seed of nematode-resistant varieties. And using management practices that maintain plant vigor throughout the growing season.
He and other Western alfalfa growers have been battling stem nematodes since the advent of sprinkler irrigation. While surface irrigation favors root nematodes, overhead water delivery systems have proved to be an inadvertent catalyst for the spread of the above-ground version.
Stem nematodes cause the most damage over winter. Symptoms include poor spring growth distinguished by bare patches, and swollen, distorted buds that are unable to elongate into normal stems. When nematodes migrate into the leaves, the tissue turns white, resulting in a symptom known as white flagging.
Stressed stands are especially vulnerable.
“Growers should avoid stressing their plants, whether it involves water, nutrients or weeds,” says Saad Hafez, a University of Idaho extension nematologist.
Callahan reduces competition by spraying his fields for weeds and volunteers before planting. He avoids buying seed offered at bargain-basement prices. Instead, he goes with proven multileaflet varieties known to stand up to nematodes and other yield-robbing pests.
“I believe you have to start with good-quality seed,” he says. “It has to have, at the very least, moderate resistance or I don't even look at it.”
“Planting varieties with high levels of resistance is probably the best management tool available, especially when alfalfa is grown on irrigated land,” says Hafez. “Without some level of resistance, a stand is at real risk.”
Cultural practices also can impact stem nematodes, he adds. Unlike root knot and root lesion nematodes, alfalfa stem nematodes are relatively host-specific. So rotation with non-host crops such as small grains, beans and corn can be highly effective in controlling their populations.
Callahan adheres to a strict rotation program, with his alfalfa stands running three years in straight alfalfa followed by two more years with interseeded orchardgrass. Then he rotates to spring-planted potatoes, fall-planted triticale, spring-planted silage corn, fall-planted triticale and finally back into spring-planted alfalfa.
“Whether it's through mechanical or chemical means, we try to not leave any live tissue in the field between crops,” he says.
Irrigation timing is also a deciding factor. University of Idaho researchers have determined that drying out fields before cutting can prevent reinfection. Hafez recommends that the top 2-3" of soil be dry before alfalfa is cut.
Callahan spikes his water and shuts down about a week before removing hay. The soil surface is dry enough to raise dust when he bales.
For him, there's no magic bullet to protect his crop against pests like stem nematodes. Instead, it's a series of conscious decisions that focus on producing the highest-quality hay possible.
“Do the right things and take good care of your forage and it will take care of you when it comes time to sell,” he says.