Warm Fall Temperatures, Winter Annual Weeds Favor SCN

Warm Fall Temperatures, Winter Annual Weeds Favor SCN

Iowa weather this fall has been wonderful for many autumn tasks but as it turns out, soil temperatures above 50 degrees F are also good for the growth of soybean cyst nematode juveniles. Do you need to test your soil for SCN?

"We have had a wonderfully sunny, warm, dry fall so far this year," says Greg Tylka, Iowa State University Extension nematologist. "How could anyone complain about the weather?  Leave it to a nematologist."

A recent ISU Integrated Crop Management newsletter has an ICM News article that reminded growers and agronomists to delay application of anhydrous ammonia fertilizer until soil temperatures drop below 50 degrees F. It turns out that 50 degrees F is also an important temperature to consider for soybean cyst nematode (SCN).

"The winter annual weeds chickweed, henbit and purple deadnettle are good hosts for the soybean cyst nematode," says Tylka. "But SCN juveniles do not develop in roots when temperatures are below 50 degrees F. So cool fall and spring temperatures usually keep SCN reproduction on these winter annual weeds in check. Such may not be the case this fall."

ISU's Soybean Cyst Nematode web page has recommendations

The chances of having soil temperatures at Ames in central Iowa below 50 degrees F on Oct. 19 are estimated to be 75% (see ISU 4 inch soil temperature probabilities). But today - Oct. 20, most of Iowa still has soil temperatures in the mid 50s F (see figure on the accompanying map). 

Growers and agronomists managing SCN-infested fields with significant populations of winter annual weeds should be aware that considerable SCN reproduction could be occurring on these alternative hosts this year. See the ISU Soybean Cyst Nematode web page for more information and recommendations about the biology, scouting and management of SCN.

Soil temperatures on October 20, 2010, at a 4 inch depth (Source: Elwynn Taylor, ISU 4 inch soil temperature map).

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