By Greg Tylka and Meaghan Anderson
Soybean cyst nematode (SCN) is a major yield-reducing soybean pathogen in Iowa, but numbers can drop as much as 50% when nonhost corn is grown. This decrease in egg numbers contributes greatly to overall management of the nematode. SCN reproduces well in greenhouse studies on the winter annual weeds henbit, pennycress, and purple deadnettle. Consequently, there is concern that large, uncontrolled infestations of these weeds (see image) could allow for increases in SCN egg numbers in the soil and somewhat negate declines in SCN egg numbers that occur when corn is grown.
There is no published information on how much soybean yield loss from SCN might occur, if any, due to the situation described above. SCN is a cold-blooded animal, and fall and spring soil temperatures affect how rapidly the nematode completes its life cycle and produces eggs. Nonetheless, it would be unwise to ignore the possibility that reproduction on weeds could diminish the overall drop in SCN numbers when corn is grown. And conceivably, the SCN reproduction could result in some degree of unnecessary soybean yield loss when soybeans are grown after corn.
While it is too late to effectively manage henbit this spring in most fields, a timely fall herbicide application would be warranted in fields that had significant infestations this spring. Also, it will be important to collect soil samples to determine SCN egg population densities this fall before growing soybeans in these fields in 2027. Sample results will reveal the SCN situation for next season’s soybean crop.
Source : iastate.edu