Control of Colorado Potato Beetle with Natural Product Insecticides, Rosemount, 1990

Abstract

Abstract Natural product insecticides used in this experiment were Bacillus thuringiensis var. san diego (MYX 1806), and B. thuringiensis var. tenebrionis (Trident and BK-102) and azadirachtin (Margosan-O RH 0000 and RH 9999) from the neem tree, Azadirachta indica. Certified B-size seed potatoes were planted 23 May at the Plant Pathology Farm, Rosemount Agricultural Experiment Station, University of Minnesota. Plots were 6 rows wide, 19.8 m (65 ft) long, with 102 cm (40 in) spacing between rows and 30 cm (12 in) between plants. Plots were separated on all sides by 2 m (6.7 ft) of cultivated soil. A completely randomized plot design with 4 replications was used. Plots were scouted daily for CPB egg masses beginning 15 Jun. When egg masses were found these were flagged and checked daily for hatch. Timing of first spray application was based on egg hatch. Three basic spray schedules were used: first application on 30% hatch of flagged egg masses and subsequent applications on either a 7 d or 10 d schedule, or first application on 30% hatch of all eggs (unflagged) laid on or before that sampling date and subsequent applications on a 7 d schedule. Plots were sprayed 1-4 times for each generation of CPB larvae. Spray dates were: 21 Jun (30% hatch of flagged eggs—1st generation), 25 Jun (30% total hatch—1st generation), 29 Jun, 1, 2, 5, 9, 20 Jul (30% hatch of flagged eggs—2nd generation), 25 Jul (30% total hatch—2nd generation), 27 Jul, 30 Jul, 1,3, 8, 9, 10 and 15 Aug. Insecticidal sprays were applied using a tractor-drawn boom sprayer with drop nozzles, 3 hollow-cone drop nozzles to the row. Sprays were applied in 795 liters water/ha (85 gal/acre) at 620 kPa (90 psi). All data was collected from the center 4 rows of each plot. CPB larvae (small = 1st and 2nd instar, large = 3rd and 4th instar) were counted on 20 randomly selected whole plants/plot. On one sampling date, 6 Jul, CPB counts were based on only 10 plants/plot and not recorded by size-class. PLH nymphs and green peach aphid apterae were counted on 35 mid-plant leaves/plot. Leaf loss to defoliation (by CPB) was estimated visually (by 2-5 individuals per sampling date) as percent foliage lost. Hopperburn (the injury caused by PLH) was estimated visually (by 2-5 individuals/sampling date) on a 0-6 scale, 0 = no injury. CPB were counted on 26 Jun, 6, 31 Jul, 8, 15, 20 and 28 Aug. PLH were counted 3, 10, 16, 24 and 31 Jul, 6, 13, 21 and 29 Aug. GPA were counted 3 Jul, 6, 13, 21 and 29 Aug. Defoliation was estimated 29 Jun, 2, 5, 10 and 16 Jul, 2, 7, 10, 16, 23 and 30 Aug. Hopperburn was estimated on 10, 16, 23 and 30 Aug. Data was expressed as mean insect numbers or plant injury × number of days elapsed (= Area Under Curve). AUC for CPB was calculated separately for 1st and 2nd generations, and then combined. For calculation of AUC for 1st generation CPB the 6 Jul counts were multiplied × 2 and included in the column CPB large. Two way analysis of variance was used to test for treatment differences in pest densities, plant injury and yield. Yields were obtained 17 Sep by harvesting one center row from each plot.