By Erin Hodgson and Ashley Dean
Corn rootworm egg hatch in Iowa occurs from late May to the middle of June, with an average peak hatching date of June 6 in central Iowa. In 2020, the expected hatching date will be behind the average due to cool spring temperatures. Development is driven by soil temperature and measured by growing degree days. Research suggests about 50% of egg hatch occurs between 684-767 accumulated degree days (base 52°F, soil). Most areas in Iowa will reach peak corn rootworm egg hatch in 5-7 days (Figure 1).
To predict corn rootworm egg hatch for your area based on degree day accumulation, use the ISU Agronomy Mesonet website. Set the start date to January 1 of the current year, use the current date for the end date, and make sure the plot parameter is set to “soil growing degree days (base = 52).” Be aware that some locations are having technical difficulties with the soil temperature probes this year.
A severe corn rootworm larval infestation can destroy nodes 4-6; each node has approximately 10 nodal roots. Root pruning interferes with water and nutrient uptake and make the plant unstable (Photo 1). A recent meta-analysis showed a 15% yield loss for every node pruned back to 1/5 inches.