Across the corn belt depending on time of year | Adult rootworm traps and counts are useful in estimating rootworm pressure but as pointed out previously, a number of factors between the trap count and the next June influence whether counts are accurate in predicting the next season's rootworm pressure.
Northern corn rootworm (the green ones): Where there is a significant presence of NCR adults on the traps, farmers should consider the issue of extended diapause. Eggs laid by these individuals hatch across a 3 yrs period. Some hatch the following June while some hatch the following two growing seasons. Why does this matter? NCR laying eggs in the final year of corn before rotating to beans next year will result in rootworm damage the year following beans due to the delayed hatching of NCR eggs due to extended egg diapause.\
Western corn rootworm:
1) traps in corn: High numbers of adults strongly suggest the field will have a rootworm problem the following year if corn is planted. This scenario is the most reliable predictor. Low numbers on traps suggests a lower rootworm pressure in the following growing season, but the count predictive value is also directly influenced by the timing and duration of the traps in the field. There are numerous cases where the traps were pulled too early and did not detect the females gravid with eggs entering the field from the neighbors, 3 wks after pollination. It is the female counts that really predict the problems the following year, not the males which make up a majority of the population around pollination. Females emerge later.
Traps counts between "light" and "heavy" have much less predictive value given the other variables in the system. In the cases of very light trap catches and very heavy trap catches, the trap results are useful. In between, it is a crap shoot.
2) traps in soybeans: Adult rootworm caught on these traps indicate the rotation resistant variant is present in the area, eggs are being laid in soybeans and the risk of rootworm damage on 1st year corn is higher.
One important variable to remember: Rootworm hatch is around June 1. Field capacity soils (extremely wet) during the hatching period drown the newly hatched larvae and regardless of the number of eggs laid, have a significant impact on the rootworm pressure. The excessive rainfall in western Iowa in May 2024 is a perfect example of this. |
Rootworm traps
