Producer’s Choice Seed and Cal/West Seeds recently hosted a seminar to discuss the 2009 and 2010 stem nematode outbreaks in northern San Joaquin Valley, the Delta and lower Sacramento Valley. It was noted that alfalfa growers have been hit the hardest with estimated losses of more than $50 million a year. Some growers have lost their entire alfalfa crops.
Why are we seeing such an increase in stem nematode infestations? Jon Reich, executive vice president of Cal/West Seeds, introduced a panel of nematode and alfalfa experts to discuss possible causes, symptoms of nematode outbreaks and what growers can do to curb increased infestations.
Watch for symptoms
Dan Putman, University of California, Davis, agricultural productivity and Extension agronomist, and Rachael Long, Farm Advisor in pest management and field crops, kicked off the seminar by giving an overview of the stem nematode problem in California and symptoms growers should watch for: stunted and patchy growth, uneven crop height, circular stunted areas and yield reduction – all signs that you may have nematodes.
Another noticeable symptom called “white flagging” sometimes occurs when a stem nematode attacks the alfalfa host resulting in an albino stem. Don Miller, director of product development for Producer’s Choice Seed, uses white flags as indicators that a field may be infested. “While doing in-field alfalfa consultations, I can tell there are stem nematodes just by seeing white flags,” he says.
Another indicator to watch for is swollen crown buds. Stem nematodes attack the plant by injecting a digestive enzyme, then burrowing into the host causing swollen “tumors” to appear. Each tumor can contain thousands of stem nematodes. With a reproductive cycle of 300 eggs every 30 days, the damage can quickly destroy the host.
Soil sampling key
Internationally recognized expert nematologist, Saad Hafez, Extension professor of nematology, University of Idaho, discussed the biology of stem nematodes, soil and plant sampling methods and benefits of crop rotation for nematode control. Emphasizing the importance of soil sampling before planting, Hafez recommends, “Test when the soil’s moist, because nematodes are aquatic creatures. Dry soil may contain millions of eggs, but unless the soil is irrigated, you won’t find evidence of a nematode infestation.
Take 2-3 samples from the root zone per acre in a zigzag pattern.” He also recommends using crop rotation as a way to control harmful nematode populations. “When rotating out of alfalfa, plant a non-host crop, such as small grain, beans or corn, for 2-4 years to reduce the nematode population in the soil.”
Breeding resistant varieties
Dr. Miller talked about the advances being made in breeding nematode-resistant alfalfas, and the rating system used to label resistant strains. Cal/West Seeds has been working for 15 years developing improved strains of alfalfa that are far less susceptible to stem nematode damage.
Typically, it takes three generations of plant breeding to eliminate a susceptible gene, but steps forward are being made everyday creating hardier strains of alfalfa.
The current rating system for labeling a plant’s resistance is on a scale of 0% to 100% with 0% – 5% being classified as Susceptible (S), 6% – 15% being Low Resistance (LR), 16% – 30% Moderate (M), 31% – 50% being Resistant (R) and 51% and above being High Resistance (HR).
That means a grower facing infestations should choose a variety with at least an “R” or an “HR” rating for Stem Nematode, if past or current infestations have been severe in his county.
One limitation of the rating system is that an HR rating is any seed above 51% meaning you might get a seed performing at only 51% or as high as 100%. There’s no way of telling what you’re getting.
Miller addressed the concern stating, “I wouldn’t be opposed to a new rating system that more accurately represents the quality of seed in the HR category – possibly an additional category: “VHR” meaning Very High Resistance.”
This alfalfa grower seminar ended with a hands-on workshop held by Lei E of Cal/West Seeds and a tour of their research facilities and greenhouses. Attendees were given information and tips vital to combating the current stem nematode problem in their own fields. Program organizers hope that through continuing education they will see a more profitable 2011 for California alfalfa growers.