BY DOUG SCHMITZ
AMES, Iowa — While the extremely wet weather in 2019 didn’t stop the spread of soybean cyst nematode (SCN), the best way farmers can manage the disease in 2020 is by soil sampling, according to an Iowa State University (ISU) nematologist.
“I am not sure there is anything specific farmers need to do (this) spring for SCN management as they most likely have made seed and seed treatment decisions for 2020 by now,” said Greg Tylka, an ISU professor of plant pathology and microbiology, and a world-renown SCN expert.
“But all farmers should sample fields for SCN to assess the population densities (numbers) in the soil if the fields have not been sampled in recent years,” added Tylka, who leads the SCN Coalition. “Sampling can be done in the fall, next fall, after harvest.”
Tylka, who’s been tracking the spread of SCN for nearly 20 years, said as of 2019, SCN has been confirmed in every county in Illinois and Iowa, and all but two Indiana counties.
In addition, about once every three years, Tylka surveys nematologists, plant pathologists and agronomists from soybean-growing states and Canadian provinces to gather updated information on counties known to be infested with SCN.
Since 2017, the last time he updated the SCN distribution map, SCN had spread to new counties in 17 states: Alabama, Georgia, Indiana, Iowa, Kansas, Kentucky, Minnesota, Missouri, Nebraska, New Jersey, New York, North Carolina, North Dakota, Ohio, South Dakota, Virginia and Wisconsin. (Tylka said he will be polling his peers again to update the map this spring.)
Soybean plants infected with SCN have poorly developed root systems, reducing the plants ability to efficiently utilize water and nutrients. Stunting, yellowing, early death, and low yields are common symptoms of nematode injury in soybeans.
Tylka said SCN-resistant soybean varieties should be grown on infested fields and farmers should work hard to obtain varieties with the hard-to-find Peking source of SCN resistance.
He said that’s because “the common PI 88788 SCN resistance is steadily losing effectiveness (leading to the buildup of high SCN numbers in the soil and thus, the need for fields to be sampled).”
“Also, SCN numbers will be reduced by five- to 45-50 percent by growing corn, a non-host,” he added. “The percent decline varies among years and fields. The number decline is less in second- year corn and becomes negligible after two years of corn.”
That’s why farmers need to know their numbers, he said.
“You can’t manage something that you don’t know you have,” he said. “Management starts with sampling. You need to know what fields have it and at what levels. That sets the stage for how you’ll want to approach the battle.
“If you catch numbers when they’re relatively low or moderate, it’s a fairly painless rotation to non-host crops like corn, oats, wheat, alfalfa, or sunflower,” he said.
“Then, get to know more about the different types of SCN-resistant soybean varieties that are available, which ones are more effective than others, and how to rotate them properly,” he added.
Tylka said growers and agronomists should also consider checking for the presence of SCN in fields that have areas that mature earlier with no apparent reason.
“Soil samples should be comprised of well-mixed soil obtained from soil cores collected from 15 to 20 different locations within an area of 20 acres or so,” he said.
“Each core should be collected from a total depth of 6 to 8 inches,” he added. “Large fields should be divided up into smaller areas from which a 15- to 20-core soil sample should be collected.”
In addition, Tylka recommends farmers use new nematode-protectant seed treatments on the SCN-resistant soybeans.
Funded by the Soybean Checkoff, the SCN coalition is a group of U.S. university researchers, extension specialists and agricultural company representatives who are concerned about the growing threat from SCN.
The coalition has compiled an updated chart of nematode-protectant seed treatments currently available, which includes crops, targeted nematodes, active ingredient and mode of action.
The chart is available at: https://www.thescncoalition.com/application/files/3615/7911/7059/2200-004-20_Seed_Treatment_Chart_11.pdf