Steven Newsom has learned to live with verticillium wilt by limiting irrigation and cutting the alfalfa early.
Newsom, who also grows triticale, seed grains and cotton under center pivots at Levelland, TX, got into the alfalfa business about four years ago. He obtained land that had been in cotton. Unfortunately, lingering in the soil was verticillium, a common cotton disease. And it didn't take long for the fungus to attack part of his alfalfa crop.
This soilborne disease is much like fusarium. It can survive years without a host and is spread by soil movement, irrigation water, bad seed or even contaminated equipment. While the disease thrives in warmer climates, it's found virtually everywhere alfalfa is grown - even as far north as Minnesota and Wisconsin.
Symptoms include one or more leaflets turning a blotchy yellow. Stems remain green and erect as leaves yellow. Stems later turn yellow-brown but remain erect with leaves attached. Internally, stems show a light orange discoloration near the plant crown or even higher as the disease progresses.
"The fungus is more common in the more aggressive varieties," says Terry Wheeler, research plant pathologist at Texas Ag Experiment Station in Lubbock. "It expands inside the vascular system, the area that carries water up and down the plant. It plugs it up. Once that happens, there's really nothing one can do to protect the plant."
Newsom's problem first surfaced in 1995 after several days of rain hit the field. Five days after the field was drenched, the alfalfa wouldn't bloom and the leaves turned yellow.
"It was on a one-year-old field," Newsom recalls. "I cut the hay, and the problem didn't return until another wet spell hit."
He and his consulting agronomist determined it was verticillium wilt. The agronomist recommended that Newsom limit his watering.
In normal situations, Newsom waters 21 days after cutting. Hay is cut again at 28 days. For the wilt-infested variety, WL 323, he waters a few days after cutting, then cuts again in 22-25 days. If rains cause the disease to kick in before then, he gets into the field immediately.
With this pattern, the field yields seven cuttings a year, one more than with a 28-day cutting schedule. Yields are a little below the 1 1/2-2 tons/acre he shoots for, but quality is high.
Texas A&M's Wheeler says a limited watering program is about the only way to manage the disease, other than planting resistant varieties. Otherwise, susceptible alfalfa will develop a wilt problem virtually anytime it receives excessive water. Stand life will be shortened.
Newsom planted a resistant variety - WL 322HQ - beside the susceptible WL 323.
"It's grown under the same pivot as the aggressive 323, and will often yield 1/2 ton/acre more because it isn't harvested as soon as the susceptible variety," he says. "My protein rating for 322 is 24%. It's about 18% for 323 if it's cut at 28 days, and 24% when it's cut at 22 days."
Wheeler advises growers to use a limited watering program similar to Newsom's to manage the disease, and to choose resistant varieties the next time they seed alfalfa.