Stem nematode is becoming such a problem in Western alfalfa fields that stem nematode-resistant varieties – at this point the only way of controlling the pest – will have to become more resistant. So says Don Miller, director of development and an alfalfa breeder with Producer’s Choice Seed and Cal/West Seeds.

“Years where stem nematodes aren't extremely bad, the resistance level in the 30-50% range has been good enough,” Miller says. “It looks like what we're seeing in California is that we need a bit higher high resistance than what we have now.”

Part of the reason the nematode is severe this year is because the West's cool, wet weather has been ideal for the pest to survive. So much so that not only first cutting, but also second cutting was damaged in northern California and the Pacific Northwest, he adds. Up to 50% yield losses have been reported in parts of some first-cutting fields in the Sacramento Valley as well as severe damage in southern Idaho and the Delta, UT, area.

As temperatures warm, the nematode stops feeding, but Miller's concerned it will be back again this fall as conditions cool. So his companies' plant breeders have been “gearing up” to add 10% or more resistance to highly resistant (HR) alfalfa varieties. Most current varieties on the market claiming the HR designation are actually just over 50% resistant. It will take one and a half to two years to get 60% or more resistance into those existing lines, he says.

Miller and colleagues are also planning an Aug. 25 Stem Nematode Seminar/Workshop in Woodland, CA, to help teach growers how to identify and keep the pest from spreading.

“Part of the problem in California is that growers weren't familiar with stem nematode and didn't know how to identify it,” he says. “They need to be more aware of it. We'll actually take them to the field and bring plants in and let them look at them. We'll have a discussion on management. Some people think they can just go out there and spray like for aphids, but that's not a possibility at this time.”

The workshop will be held at the Cal/West Seeds Research Center and is sponsored by Cal/West Seeds and Producer's Choice Seed. Registration starts at 8 a.m., and the program will run from 9 a.m. to noon.

Dan Putnam, University of California Extension forage specialist, and Rachael Long, UC Extension farm advisor, will take part in the program with Saad Hafez, University of Idaho nematologist, as well as Miller, Cal/West California breeder Lei E and Jon Reich, a Cal/West research and development executive.

To preregister by Aug. 13, email c.souza@calwestseeds.com or call 530-207-5102.

For more on stem nematode, including management tips, watch for the August issue of Hay & Forage Grower.