SANDEA–SOIL INSECTICIDE INTERACTION STUDIES IN NORTH CAROLINA POTATOES

in HortScience
Authors: R.B. Batts1 and A.W. MacRae1
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  • 1 North Carolina State University, Raleigh, NC and University of Georgia, Tifton, GA

Trials were conducted at Plymouth, NC in 2004 and 2005 to determine the effect of halosulfuron on the yield and grade of white-skinned and red-skinned Irish potatoes when used in combination with different infurrow insecticides. Factors for the factorial design used included potato variety, halosulfuron timing, halosulfuron rate, and insecticide. In-furrow insecticides included imidacloprid. aldicarb, and phorate at 30.3, 293, and 233 g ai/1000 m of row, respectively. Halosulfuron was applied at 26.3 or 52.6 g ai/ha preemergence (PRE), postemergence, over the top (POST), or postdirected (P-DIR) to the potatoes. Preemergence applications of halosulfuron were made after last hilling of the bed, POST applications were made at early flowering, and P-DIR sprays were applied at late flowering. Crop injury was evaluated visually at 2 and 4 weeks after treatment (WAT). Potatoes were dug and graded at maturity. Data was subjected to analysis of variance (ANOVA) with means separated using Fisher's protected LSD (p = 0.05). No interaction between insecticides and halosulfuron were observed. However, some yield differences were seen due to halosulfuron alone. Minimal (<10%) injury was seen with PRE and P-DIR applications. Substantial injury was only seen at 2 WAT, and only from POST treatments. At this timing, halosulfuron applied at the low rate injured potato 14-19% across the insecticides, while the high rate caused significantly higher injury (23% to 24%). Injury from the POST timing did affect yield. Higher levels of smaller potatoes (USDA Grade #1) were found in the POST treatments, when pooled over years, varieties and rates. This indicates that tuber development may have been delayed due to foliar injury. This is supported by the lower levels of USDA Grade #3 potatoes from POST applications compared to other timings. When pooled across years, varieties, and rates, the lowest total yields were with the POST timing.

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