Effects of Insecticides on Cutworms and on the Yield and Quality of Flue-Cured Tobacco, Ontario, Canada, 1985

Abstract

Abstract Twelve insecticidal treatments, including foliar- and soil-applications, were evaluated to determine their effects on darksided cutworms and on the yield and quality of flue-cured tobacco at the Research Station, Agriculture Canada, Delhi, Ontario. Plots measured 76 × 14 ft and were arranged in a randomized block design with 4 replications in each treatment. Each plot consisted of 4 rows of tobacco with 38 plants in each row, the outside 2 rows in each plot being guard rows. Tobacco seedlings of the variety Candel were transplanted into a field of Fox loamy sand on 28 May. Furthermore, 2 subplots (12 × 12 inches each) were established in each plot. Test insects were 4th and 5th-instar larvae for rye treatment and 6th and 7th-instar larvae for soil and tobacco seedling treatments. The insecticides were broadcast evenly on the rye cover crop on 17 Apr, soil surface on 16 May, and on tobacco seedlings on 5 Jun, using a power sprayer equipped with 80-04 Tee Jet nozzles applying 25 gal of liquid per acre at 3.4 mph and 32 psi. Ten larvae were placed in each subplot 2 hours before treatment. The larvae were retained in the subplots by aluminum barrier strips 8 inches high with 3 inches embedded in the ground to prevent the larvae of the darksided cutworm from escaping. Mortality counts of the larvae in the subplots were made daily for 5 days. Abbott’s formula was used to correct for the mortality occurring in the untreated check. Cutworm damaged plants from the 2 central rows in each plot were counted on 12 and 20 Jun. The number of damaged plants recorded in the last count was expressed as a percentage of the total number of original plants within the 2 center rows of each plot. The harvest and curing of each plot were carried out in the conventional manner. Cured tobacco leaves were analyzed for reducing sugars and total alkaloids as measures of the quality of the tobacco. Agronomic parameters measured were yield (lb/acre) and grade index (0/lb). The percentages of cutworm mortality in the subplots and plants damaged per plot were transformed to angular units before analysis of variance. Means were converted to original units for tabulation.