SCN is in 22 Ontario counties
By Jonathan Martin
Soybean cyst nematodes (SCNs) are sneaky little parasites. Farmers often can’t tell their fields are infected until they look below the surface.
The adult females cling to a crop’s root. They’re tiny, pale bumps that look a bit like miniature root nodules.
“The are quite small so you may need your glasses,” Meghan Moran; canola and edible bean specialist with the Ontario Ministry of Agriculture, Food and Rural Affairs; told Farms.com.
Female juvenile SCNs maneuver through a plant’s cells until they reach the part of the plant that transports nutrients. There, they latch on and start to feed.
As they feed, they grow until they get so big that they pop out the end of the root and become visible to the naked eye. The males fertilize them, the females lay eggs and then the females die. When the females die, their cuticles harden around the eggs and become cysts. From there, the babies develop, wait for the soil to reach the right temperature and moisture levels, hatch and the process repeats itself.
Three or four generations of SCNs can proliferate in a single growing season. They’re one of the most yield-limiting soybean diseases in North America and they can infect all types of dry beans. They’re in 22 Ontario counties right now.
In total, 80 per cent of fields tested in Ontario were SCN-positive.
Nemacides offer variable effectiveness in Ontario’s SCN-infected dry bean fields and no SCN-resistant varieties of dry beans are available.
The best option – right now, at least – is to manage risk.
“Ideally, you’re just monitoring all your fields and taking soil samples to look for SPN,” Moran said. “Don’t plant dry beans in fields that have SPN or, at the very least, choose some of the more tolerant varieties of dry beans. We think black beans may be a little more tolerant (of SPN), for example, though we don’t know why.”
Stunting, poor canopy closure, and chlorosis are good signs that a field is infected. So are plants that mature early or have fewer pods. The damage is often most apparent in sandy areas of the field.
Often, though, no above-ground symptoms are visible.
“SCM is a silent yield thief,” said Moran. “A farmer might not know their field has it, so they’ll take their equipment from one field to another and, since SCN lives in the dirt, it will spread to their other fields.”
A farmer can spot cysts 30 to 45 days after emergence by gently digging up his or her plants, rather than pulling them out.
SCN is likely to take hold earliest near the entrance of the field, along fence lines and in areas that have flooded. SCNs also like soil with a pH value greater than seven.
The best way to test for SCN is to use a soil probe to take samples at a depth of six to eight inches shortly before or shortly after bean harvest, sampling directly in the row, before tilling.
Researchers are studying ways to treat the disease, so hopefully some good news will be available soon. If there is, you can be sure Farms.com will let you know.