Control of Mint Root Borer & Wireworms in Peppermint, 1993

Abstract

Abstract In 1993, the effect of Steinernema carpocapsae (Biovector) and chlorpyrifos (Lorsban 4 E) on MRB larvae and wireworms was evaluated in a center-pivot irrigated field near Royal City, WA, USA (Grant Co). A RCB design was used for treatments replicated 4 times. Plots were 12 ft by 25 ft. Treatments included a split application of nematodes at a rate of 1 billion nematodes/acre followed by a second application at the same rate, a single application of nematodes at a rate of 1 billion/acre and chlorpyrifos at a rate of 2 qt/acre. The last three treatments were made at the second application date. Application dates were 27 Sep 93 and 1 Oct 93. The evaluation involved pre- and post-treatment sampling to determine if the field population exceeded the economic threshold of 2 to 3 MRB larvae/ft2 and evaluate the effect of an entomopathogenic nematode and chlorpyrifos on MRB and wireworm post-treatment sample populations. Pre-treatment sampling for MRB larvae began 13 Sep and continued to 20 Sep 93. In each plot, all rhizomes from a randomly selected 1-ft2 subsample were split, inspected for larvae and the soil to a depth of 3 inches was sieved for MRB larvae and wireworms. The same procedure was used to evaluate MRB larval and wireworm sample populations post-treatment. Treatments were applied using a CO2 backpack sprayer equipped with a 4-nozzle attachment that produced a spray width of 6 ft. Screens were removed from the nozzles and treatments were applied at 25 psi to reduce nematode mortality as they passed through the spray nozzles. The application regime consisted of the following. On 27 Sep 93, 3 gal water was applied with the backpack sprayer to moisten the soil surface immediately before applying nematodes, 3 gal water was used to apply nematodes to the soil surface at a rate of 1 billion/acre, and another 3 gal was applied post-application to water nematodes into the soil. On a per-acre basis, this was approximately 1300 gal of water/acre. On 1 Oct 93, the backpack sprayer was used to apply nematodes (1 billion/acre) and chlorpyrifos at 2 qt/acre with 3 gal water. Another 3 gal was immediately applied to each plot following application of each treatment. One inch of water was then sprinkled on all plots using a center-pivot irrigation sprinkling system to wash the nematodes and water into the soil.