Tank Mix Combinations of Insecticides and A Herbicide Against Cutworms and Weeds on Flue-Cured Tobacco, Ontario, Canada, 1988

Abstract

Abstract Each of the 6 insecticides and a herbicide, Devrinol, were applied in tank-mixed combinations on tobacco seedlings after transplanting to determine their effectiveness against cutworms and weeds on flue-cured tobacco in Ontario. Tobacco seedlings were transplanted into a field of Fox loamy sand on 27 May. Plots were 76 × 14 ft, replicated 4 times in a randomized complete block design, and consisted of 4 rows with 38 plants in each row. Furthermore, 2 subplots (12 × 12 inches each) containing 3 tobacco seedlings were established in each plot. Ten fifth- and sixth-instar larvae were introduced in each subplot 2 h before treatment and then 5 DAT. The larvae were retained in the subplots by aluminum barrier strips 8 inches high with 3 inches embedded in the ground to prevent the cutworm larvae from escaping. The tank mixtures of each insecticide and Devrinol were applied in a 10-inch band over the row in each plot on 1 Jun, using a power sprayer equipped with 65-06 flat nozzles applying 11 gal/acre at 15 psi and 3.5 mph speed. Cutworm damaged plants from the 2 central rows in each plot were counted weekly after treatment for 4 wk and the number of weeds was counted 2 wk after treatment. Mortality counts of the larvae in the subplots were made daily for 5 d. Toxicity and residual activity of the treatments were evaluated by collecting random leaf samples at regular intervals from each plot. Samples were taken to the laboratory and equal amounts of leaves were placed in 4-inch Petri dishes containing insecticide-free sand and 10 fifth- to sixth-instar larvae. Mortality was assessed daily for 5 d by counting the number of dead larvae in each dish. Abbott’s formula was used to correct for the mortality occurring in the untreated check. The percentages of larval mortality in the subplots and laboratory tests were transformed into angular units, and square root transformation was used for the number of cutworm damaged plants before ANOVA. Means were converted to original units for tabulation.