When rootworm corn became a reality in 2003, US farmers finally had an effective tool to control a billion dollar pest. Unlike western and southern rootworm, northern rootworm is a particular problem due to extended diapause: the ability of their eggs to survive during rotated years of beans. Likewise, the western variant found predominantly in Illinois and fringe areas of adjoining states also presents the problem of laying eggs, preferentially in bean fields. Understanding these behaviors helps to manage risks of these yield robbers and allows a management strategy to lower those risks.
Typically, when deciding whether or not to plant a rootworm corn, most farmers look at some common factors to determine their risk such as corn on corn, past history of rootworm pressure or in some cases late planted or replanted corn that tends to flower later. These cases of later planting/flowering tend to “draw in” beetles looking for a food source such as corn pollen and silks and ultimately lay their eggs for the next crop in those areas. I would suggest considering weed control in soybeans as another factor, especially late germinating waterhemp.
One troubling and somewhat new behavior that has been observed in the Midwest the past few years is the rootworm beetle feeding in patches of late germinating weeds in bean fields. University researchers have also observed that rootworm pressure the following year seems to be much higher than the rest of the field when rotated back to corn. It appears as corn hits brown silk stage and other pollen sources “dry up”, these bugs are drawn to the only available food source–in this case waterhemp pollen seems to be a favorite.
To help manage weeds in your bean fields, strongly consider utilization of effective pre-emerge herbicides, along with a post program of Xtend or Enlist soybeans, if your state allows their use for late season post herbicide applications. If you have some fields where weed escapes have been common, strongly consider the use of SmartStax corn or insecticides to control the sleeping threat of rootworm feeding in your corn. As Christmas approaches, we all hope for surprise gifts to enjoy but don’t let corn rootworm be the “gift” that ruins your 2020 corn crop.