Take the battle to SCN this summer
Soybean cyst nematode has been the buzz since it was first found in our region in 2003. Although the spread has not been rapid and infestation has not reached economically challenging levels, every soybean grower needs to be alert and know how to identify it.
Last fall, North Dakota State University Extension Plant Pathologist Sam Markell led an effort to identify counties where SCN is present. Five new counties in North Dakota, from Emmons in the west to Pembina in the north, are now listed. All Red River Valley counties, with the exception of Walsh (probably just not confirmed), were identified with SCN in soils.
I liken these results to saying all counties have yellow houses — perhaps not widespread, but present.
Because we live and farm in the North, we have an advantage that frequently these pathogens and pests spread to our region after a solution has been discovered to fight them. SCN-resistant soybean varieties have been developed — and they are the best defense against SCN. However, don’t press your luck and plant SCN-resistant varieties on non-cyst infected ground, as resistance issues could result.
Crop rotation away from crops that are good hosts (dry beans, soybeans and peas) helps to reduce the SCN numbers but will never rid the soil of the pest. SCN is a microscopic roundworm that penetrates the roots of the soybean. The females remain on the roots and swell into the lemon-shaped cysts that are visible. These cysts contain 250 to 500 eggs each, that either burst, allowing the eggs to infect other roots, or remain in the soil, dormant for many years. SCN harms soybean yields by robbing nutrients and water from the plant. Yield is affected before visual symptoms are noticed. That is why it is so important for growers in regions where SCN is spreading to scout this summer, so the problem can be identified before it robs yield.
Scouting fields is the first step in SCN management. Yield can be reduced before visual symptoms ever appear on the plants. Begin scouting about six to seven weeks after planting and examine high-risk areas, including previously flooded areas, low spots, low-yielding areas and field entrances. Dig up the plants and roots rather than pulling them, as cysts can be lost if plants are pulled from the ground. If possible, rinse the roots prior to inspection. Examine them for yellowish-colored cysts that are less than half the size of the nodules on the roots.
SCN eventually causes visual symptoms that are very similar to iron deficiency chlorosis, soil compaction, water-logged soils and other diseases. Plants will eventually become stunted and yellowed.
With the recent expansion of the SCN infestation in North Dakota and northern Minnesota, I want to get the word out to scout this summer. You’ll be better able to deal with the problem when you know what you have.
Spelhaug is an agronomist at Peterson Farms Seed, Harwood, N.D. Contact him at 701-282-7476.
This article published in the April, 2012 edition of DAKOTA FARMER.