Impact of Precipitation on the Performance of Insecticides MGWIC 2008 Final Report John C. Wise¹, Christine VanderVoort², and Rufus Isaacs 3 Michigan State University, Trevor Nichols Research Complex Department of Entomology, 205 CIPS¹, 202 CIPS 3, East Lansing, MI 48824 MSU Pesticide Analytical Laboratory² Problem Statement Michigan grape producers face an array of new challenges leading into the Twenty First Century, ranging from global competition, to the high cost of fossil fuels, to increased regulatory restrictions resulting from the Food Quality Protection Act. In relation to grape pest management it is fortunate that many new insecticide chemistries are being developed for US agriculture. In fact, in the past decade there have been more than ten new insecticides registered for use in grapes, representing four new chemical classes. One issue that is poorly understood by growers as well as the academic community is the impact of precipitation on the performance of insecticides. Michigan s spring production season regularly receives 10-15 inches of rainfall, precipitation patterns ranging widely in terms of the number and duration of events and the amount of rain for each. Very little research has been done on this subject, leaving growers to depend on folk lore to guide their decisions of whether or not they need to re-apply after a rain event. In 2006 the Michigan Agriculture Experiment Station provided funds to purchase and install a state-of-the-art rainfall simulation chamber at the MSU Trevor Nichols Research Complex (TNRC). Significant effort has been invested in 2007 to calibrate the new rain-booth to simulate various precipitation patterns relevant to Michigan s growing season. Precipitation events vary in duration, intensity (water per minute), and droplet size. Our state-of-the-art rainbooth will allow these rainfall characteristics to be measured and calibrated for repeatability. The purpose of this study is to create a research database on the rainfastness characteristics of every class of insecticide for a range of precipitation patterns that will give grape growers confidence in their decision making. We hypothesize that simulated rainfall events will reduce the insecticidal activity of many compounds (especially conventional chemical classes), but that certain new chemistries will have enhanced capability to maintain performance in the face of most patterns of precipitation. Objectives: To determine the impact of precipitation on the performance of insecticides, we will: a. Determine the impact of rainfall on insecticide control of the Japanese beetle (2008). b. Measure the loss of insecticide residue from grape leaf surface and sub-surfaces through residue profile analysis (2008).
Methods and Procedures: We initiated research at the TNRC, using the new rainfall simulation chamber to create a research database on the rainfastness characteristics of every class of insecticide for a range of precipitation patterns. The study had two experimental components with methods as follows: a) Determine the impact of rainfall on insecticide control of the Japanese beetle (2008). Field-based laboratory bioassays using Japanese beetle as the test insect were used to measure the rainfastness characteristics of insecticides under selected precipitation settings (0.5 in and 1.0 in rainfall events). Treatment compounds were field sprayed onto concord grapes with an airblast sprayer, and leaves collected and brought into the laboratory for testing. One set of field-treated leaves were held for Japanese beetle adult bioassays, and parallel samples treated with simulated rainfall in the TNRC rainbooth at the prescribed precipitation settings. Five Japanese beetle adults (collected with field traps) per replicate (5 reps per treatment) were exposed to untreated leaves, field-treated, and field-treated with rainfall simulations. Measurements of beetle mortality, knockdown and percent defoliation will be made after 72 hours of exposure. The chemicals studied were thiamethoxam (Actara ), indoxacarb (Avaunt ), bifenthrin (Capture ), Phosmet (Imidan ), and Carbaryl (Sevin ). b) Measure the loss of insecticide residue from grape leaf surface and sub-surfaces through residue profile analysis (2008). Parallel leaf samples were taken for each compound and test regime, and processes for analysis by the MSU Pesticide Analytical laboratory. Samples for each treatment were analyzed with GC or HPLC, separating surface and interior residues, so as to describe the location and extent of residue loss under the test conditions. These results are pending upon completion of analytical work by the MSU Pesticide Analytical laboratory, expected by April 2009. Results: When Japanese beetle were exposed to fresh 24 h old residues, all compounds caused high levels of adult mortality, with Capture, Sevin and Imidan showing the fastest activity over the 48 hours (Table 1). When 0.5 and 1.0 inch rainfall simulations were conducted, the activity of Capture, Sevin and Actara was relatively maintained, whereas for Imidan and Avaunt the effectiveness was reduced. When Japanese beetle were exposed to 7 day old field-aged residues, Sevin and Imidan caused high levels of adult mortality, while Capture, Avaunt and Actara showed moderate (Table 1). When 0.5 and 1.0 inch rainfall simulations were conducted, the activity of Actara, Avaunt, and Capture was relatively maintained, whereas for Imidan and Sevin the effectiveness was reduced. Comparing toxicity of given compounds across rainfall simulations (Figure 1) showed Actara, Avaunt and Capture to be the most rainfast, although that characteristic does not necessarily translate to the best control. The high toxicity of Imidan and Sevin on JB adults largely masks their weaker rainfastness characteristics.
Table 1. Mean ± (SD) proportion of Japanese beetles alive after exposing 5 beetles to field ages residue subjected to 0 inches, 0.5 inches or 1 inches of rainfall. 24 hr 0 in rain 0.5 in rain 1 in rain Treatment 4 24 48 4 24 48 4 24 48 UTC 1.00 (0.00) 0.92 (0.11) 0.96 (0.09) 1.00 (0.00) 1.00 (0.00) 1.00 (0.00) 1.00 (0.00) 1.00 (0.00) 0.96 (0.09) Imidan 0.24 (0.43) 0.04 (0.09) 0.00 (0.00) 0.76 (0.21) 0.44 (0.38) 0.28 (0.27) 0.76 (0.36) 0.52 (0.48) 0.40 (0.42) Sevin 0.12 (0.18) 0.04 (0.09) 0.00 (0.00) 0.40 (0.24) 0.12 (0.18) 0.08 (0.11) 0.56 (0.36) 0.32 (0.33) 0.24 (0.33) Capture 0.16 (0.17) 0.16 (0.26) 0.00 (0.00) 0.40 (0.32) 0.24 (0.43) 0.12 (0.18) 0.56 (0.33) 0.04 (0.09) 0.12 (0.11) Actara 0.64 (0.26) 0.40 (0.28) 0.24 (0.22) 0.92 (0.11) 0.60 (0.14) 0.44 (0.38) 0.56 (0.46) 0.60 (0.37) 0.20 (0.20) Avaunt 0.88 (0.27) 0.52 (0.23) 0.40 (0.28) 0.92 (0.18) 0.92 (0.17) 0.68 (0.23) 0.88 (0.11) 0.84 (0.22) 0.72 (0.27) 7 day Treatment 0 in rain 0.5 in rain 1 in rain 4 24 48 4 24 48 4 24 48 UTC 1.00 (0.00) 1.00 (0.00) 1.00 (0.00) 0.96 (0.09) 0.96 (0.09) 0.92 (0.11) 1.00 (0.00) 1.00 (0.00) 1.00 (0.00) Imidan 0.80 (0.20) 0.24 (0.22) 0.00 (0.00) 1.00 (0.00) 0.80 (0.35) 0.68 (0.41) 0.96 (0.09) 0.72 (0.18) 0.40 (0.42) Sevin 0.72 (0.11) 0.12 (0.18) 0.04 (0.09) 0.64 (0.30) 0.44 (0.46) 0.24 (0.26) 0.92 (0.11) 0.80 (0.20) 0.52 (0.33) Capture 0.84 (0.09) 0.48 (0.39) 0.68 (0.27) 0.56 (0.46) 0.60 (0.42) 0.40 (0.55) 1.00 (0.00) 1.00 (0.00) 0.80 (0.14) Actara 0.92 (0.11) 0.72 (0.39) 0.64 (0.41) 0.76 (0.26) 0.76 (0.26) 0.60 (0.42) 1.00 (0.00) 0.92 (0.18) 0.76 (0.33) Avaunt 1.00 (0.00) 0.72 (0.44) 0.48 (0.30) 1.00 (0.00) 0.76 (0.35) 0.52 (0.46) 0.96 (0.09) 0.80 (0.35) 0.64 (0.38)
Figure 1. Mean ± SD proportion of beetles alive in bioassay chambers containing leaves which received simulated rainfall after 48 hours of beetle exposure. Lack of a significant difference between a treatment proportion and the corresponding UTC proportion is indicated with an asterisk (*). A significant difference between the proportion of beetles alive at 24 hour and 7 days at the same rainfall level is indicated with a diamond ( ).
Communications Activities, Accomplishments, and Impacts The margin of profitability in Michigan s grape and wine industry is becoming ever more tight, and yet the penalty for even limited fruit injury at harvest can be catastrophic. Given the high cost of modern IPM programs, there is no room for unnecessary sprays. Understanding the rainfastness characteristics of insecticides will give grape growers confidence in their pest management decision making. The findings of these trials have and will be communicated to growers at a variety of forums, such as the 2009 SW Hort Days, Industry Webinars, and 2009 Great Lakes Fruit and Vegetable Expo. Funding Partnerships: $9,908.00 was provided for this work by the Michigan Grape and Wine Industry Council. The associated Agricultural Chemical companies (Syngenta, Gowan, FMC, DuPont, and Bayer) supported this work through their contribution of treatment compounds.