January 30, 1998
The population density of soybean cyst nematodes is high in many fields in southern Minnesota. It would be a good idea to plant these fields to a crop other than soybeans, says a University of Minnesota plant pathologist.
Senyu Chen, who works at the U of M Southern Experiment Station at Waseca, cites a 1996 survey of soil samples collected from counties in southern Minnesota. The survey indicated that 35 percent of these samples contained more than 10,000 nematode eggs per 100 cubic centimeters of soil.
"These fields should be planted to non-hosts or poor hosts for two or more years to reduce the nematode population to below 1,000 eggs per cubic centimeter of soil before planting a nematode-resistant soybean variety," says Chen. "Crops that are non-hosts or poor hosts include corn, alfalfa and peas."
Chen says planting a nematode-resistant variety is not enough to prevent significant yield losses in fields with high nematode population densities. "A resistant variety reduces nematode reproduction rates, but can't prevent nematodes from penetrating soybean roots," he points out. "If large numbers of nematodes are in the soil, nematode penetrations can cause significant damage to soybean roots and reduce yield."
Chen conducted a study at Lamberton last year on the correlation between ematode egg (over) density and soybean yield. The study began in 1996 in a field nfested with a high nematode density. Forty-eight plots were established in the field and planted to 12 soybean varieties with various levels of nematode resistance. By the spring of 1997, egg counts in the field ranged from 50 to 38,500 eggs per 100 cubic centimeters of soil.
In 1997, the plots were planted to Freeborn, a nematode- resistant soybean variety. Yields were measured in the fall.
"Yield of the resistant variety in 1997 was negatively correlated with nematode egg density in the fall of 1996 and egg density in the spring of 1997," says Chen. "In plots with high egg density, soybean plants were stunted and the canopy did not close, while in plots with lower nematode egg counts, soybean plants were tall and vigorous. About 12 bushels of yield reduction per acre occurred in plots with about 38,000 eggs per 100 cubic centimeters of soil, compared with yields in plots with about 1,000 eggs per 100 cubic centimeters of soil."
Chen says that although yield was significantly lower in plots with high nematode density, there were no obvious above- ground symptoms except that plants were smaller.
Chen says soybean producers who want to determine the nematode density in their fields can send a soil sample to the Plant Disease Clinic in the U of M Department of Plant Pathology. Details on collecting and submitting samples are available from county offices of the University of Minnesota Extension Service.
Chen is a faculty member in the College of Agricultural, Food, and Environmental Sciences.
Web,V2MN,F4
NEXP5690
Source: Senyu Chen, (507) 835-3620
Editor: Joseph Kurtz, EDS, (612) 625-3168,
pkurtz@extension.umn.edu
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