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ESTIMATING CORN ROOTWORM

ESTIMATING CORN ROOTWORM BEETLE POPULATIONS WITH STICKY TRAPS return to table of contents by Jeff Mathesius, Agronomy Research Manager OBJECTIVES • Quantifying corn rootworm beetle populations in the summer allows growers to make better informed decisions regarding management options the following season. • A survey was conducted in 2016 to estimate corn rootworm population levels in fields throughout the Central and Northern Corn Belt using Pherocon ® AM/NB sticky traps. STUDY DESCRIPTION Year: 2016 Locations: Sampling Methods: 773 fields in Iowa, Illinois, Minnesota, Nebraska, and South Dakota • Sticky traps placed in field beginning at blister stage (R2) • Sticky traps placed per field: 1 or 6 • Beetles counted on each trap at 7-day intervals with the average per trap recorded • Trapping continued for 4 to 6 consecutive weeks. • Trapping was conducted in both continuous corn and corn-soybean rotated fields. Northern corn rootworm Western corn rootworm RESULTS • Corn rootworm population levels were categorized at zero, low, moderate, or high for each sampling location in 2016: »» Zero = no beetles collected »» Low = traps average < 21 beetles/week »» Moderate = traps average 21 - 50 beetles/week »» High = traps average > 50 beetles/week • Maximum corn rootworm beetle population levels observed by location across all weeks (Figure 1 and Figure 2): »» 8.4% of locations had high populations. »» 10.9% of locations had moderate populations. »» 75.8% of locations had low populations. »» 4.9% of locations had zero adults collected. • Previous crop appeared to influence beetle populations. Across all locations, the average maximum count for corn after corn was 21.6; whereas, corn after soybean was 7.6 (Table 1 and Figure 3). Corn Rootworm Beetle Count 450 400 350 300 250 200 150 100 773 Locations 4.9% - Zero Beetles 75.8% - 50 Beetles (High) 50 0 Figure 1. Population levels observed at corn rootworm beetle trapping locations in 2016. 106

eturn to table of contents RESULTS Zero = no beetles collected Low = 50 beetles/week collected Figure 2. Maximum population levels observed at corn rootworm beetle trapping locations in 2016. Table 1. Effect of previous crop on maximum beetle count averaged across all locations. Previous Crop Average Beetle Count Locs Corn 21.6 408 Soybeans 7.6 305 Corn Soybeans Other Figure 3. Previous crop at corn rootworm beetle trapping locations in 2016. ACTION THRESHOLDS Traps average 50 beetles in a single week. • High rootworm populations anticipated next year. • Select a control option for high populations: »» Rotate to another crop. »» Apply foliar insecticide in the current year to control adult beetles prior to egg-laying, and use a rootworm resistant Bt corn or soil-applied insecticide the following year. »» Consult with your Pioneer sales professional, university extension, crop consultants, or other local experts for recommendations if considering planting a corn rootworm Bt corn product and adding a soil-applied insecticide. MANAGEMENT CONSIDERATIONS • Although DuPont Pioneer studies have shown that the HXRW trait remains an effective tool for corn rootworm management, DuPont Pioneer and university research suggests that continuous, uninterrupted use of the same corn rootworm Bt technology can lead to decreased corn rootworm susceptibility to that technology and may result in reduced product efficacy against these insects. • To help maintain the efficacy of Bt corn rootworm products, it is essential to develop a multi-faceted rootworm management plan. • Your Pioneer sales professional or local extension professionals can assist you in developing best management practices for your operation. • Please contact your authorized Pioneer representative or consult with your local university extension for more information regarding insect resistance management, best management practices, and to understand whether there has been insect resistance documented in your area. 107

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