SENECA FALLS, NY – As the soybean cyst nematode (SCN) has made inroads in New York State and other parts of the Northeast, farmers should remain vigilant for its appearance – and make plans to address it before it proliferates.
Dr. Kathryn Bushley with USDA-Agricultural Research Services in Ithaca presented “Soybean Cyst Nematode: An Emerging Pest In New York” as part of a New York Soil Health Field Day recently, hosted by Rodman Lott & Son Farms.
“Soil is an incredibly diverse environment,” Bushley said. “In one gram of soil, there are billions of bacteria, millions of fungi and thousands of nematodes and protozoa. There are very complex interactions among them.”
She listed the types of nematodes, including roundworms, plant parasitic, animal parasitic and bacterial and fungal feeding. The SCN, Heterodera glycines, “causes the largest yield losses to soybeans in the U.S.,” Bushley said.
They account for more than 30% of total soybean losses, totaling more than an estimated $1.5 billion annually. The five-year average loss is 119.99 million bushels, compared with seeding disease (46.21 million), charcoal rot (43.92 million), sudden death syndrome (40.54 million), Phytophthora rot (31.84 million), Sclerotinia stem rot (18.54 million) and brown stem rot (19.09 million). The distribution of SCN reflects the areas of the country with the top production of soybeans.
“It’s kind of an unseen killer in the soil,” Bushley said.
She explained that the invasive pathogen originated from Asia and spread quickly throughout America’s soybean growing regions, likely in soil on boots or equipment, as nematodes are not airborne. Each nematode cyst contains 200 – 500 eggs, making their proliferation rapid. Plus, the SCN can live up to 10 years.
“The cyst is a protective structure,” Bushley said. “It’s impossible to eradicate it.”
Its 30- to 35-day lifecycle enables it to reproduce two to three times per growing season in the Northeast. The pest is mostly obligate with soybeans.
Ninety-five percent of resistant cultivars use a single resistance locus, P188788, but many types of SCN have already overcome resistance.
“I don’t mean to be a doomsdayer, but we have about another decade of effectiveness,” Bushley predicted.
Nematicides work, but the U.S. has banned most of these because they also kill non-targeted organisms, and they have other environmental and health risks.
She said that crop rotation – the soil-conscious farmer’s go-to strategy – can help reduce SCN populations.
Only a few biological controls exist: Poncho/VOTiVO and Clariva (brand name biocontrols) and Abamectin and DiTera (biopesticides). As effective as some of these methods are, unfortunately, there’s no silver bullet for SCN.
“It’s not one solution; you have to throw everything at it,” Bushley said.
In her research while at the University of Michigan, in an area where SCN has been established for more than 40 years, crop rotation and the other strategies to help improve soil health reduce the load of SCN. Interestingly, continuous soybeans for 20 to 30 years creates “suppressive soil” that keeps SCN numbers down to manageable levels.
“There are lots of theories about why,” Bushley said. “Over time, the microbes might be helping to control it. Can we isolate these bacteria and fungi?” That may represent the next step in fighting SCN.
But generally, in the short-term, continuously growing soybeans in the same field season after season reduces yield and does not promote healthy soil.
“There is a yield effect of continually cropping,” Bushley said. “You get a yield increase after a rotation.” Disrupting the SCN proliferation with a non-host crop can reduce their numbers too.
One potential tool for fighting SCN is nematode egg parasites. Another is parasitic fungi that form “traps” for nematodes in the soil anytime they detect them.
“They’re thinking of the SCN as a source of food,” Bushley said. “Another thing to think about is will these treatments persist in the soil?”
So far, experiments show that the egg parasites were the most abundant. More research will be needed to show if they will survive through a soy/corn rotation, but Bushley thinks they’re likely to persist in the soil. So far 20 fungi are shown to be effective against SCN, but more work will need to be completed to know how to use that information and the right dosage, method for application and timing. Application methods may include seed treatments and soil drenching.
“There are a lot of challenges with SCN,” Bushley said. “The most effective tool is plant genetics. Researchers need new sources of resistance. Unfortunately, SCN is moving north. There hasn’t been enough effort to bring resistant varieties into the northern varieties.”
She encourages farmers to ask seed developers for further expansion of SCN-resistant varieties that will grow in the north.