The effect of rain and sunlight on the number of microcapsules containing oriental fruit moth, Grapholitha molesta (Busck), pheromone was determined with microscopy after treating apple leaves with Phase I, III, or V OFM MEC. 'Golden Delicious' trees in the various replicates were exposed to field conditions of 0-87 mm rain, and solar radiation of 260-3,713 langleys (ly). Rainfall > 10 mm significantly decreased the number of microcapsules on field exposed leaves to 42-65% of the controls. One week of cloudless exposure to mid-July sun (3,713 ly) caused a significant decrease in Phase I and III treatments but not the Phase V treatment. Microcapsules of the Phase I formulation were more susceptible to breakdown from sunlight than Phase III and V formulations. The rainfastness of Phase I microcapsules was comparable to the Phase V and slightly less than the Phase III formulations. With the exception of the Phase I treatment in one of thirteen replicates, the spreader-sticker-extender, Nu-Film-17, did not significantly increase the number of Phase I or III microcapsules after exposure to field conditions. The top surface of leaves treated with Phase III OFM MEC had the highest number of microcapsules/cm2 on both field (3.6 ± 0.6) and control (6.5 ± 0.8) foliage. Phase III OFM MEC may be more effective in fruit growing regions with significant rainfall, whereas, Phase V may be more suited to regions with a high intensity of sunlight throughout the growing season.
Species 1: Lepidoptera Tortricidae Grapholita molesta (Oriental Fruit Moth)
Keywords: pheromone, mating disruption
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