| Summary: | Diflubenzuron (Dimilin) was evaluated as a control agent for the codling moth, Laspeyresia pomonella L. and obiiquebanded leafroller, Choristoneura rosaceana (Harris).
Laboratory tests showed codling moth eggs to be extremely sensitive to diflubenzuron, particularly when treated topically immediately after oviposi-tion. LD50 values for 0- to 2 ½ and 3-day-old eggs were 1.1 and 17.2 ppm, respectively. Diflubenzuron was more effective as an ovicide when kept in solution on egg surfaces for longer time periods. When the compound had dried on fruit or foliage, residual action was excellent against the eggs. This activity did not decrease over a 10-day period and daily spraying of foliage with water did not significantly reduce ovicidal action. Tween 20, a surfactant, improved the distribution and efficacy of diflubenzuron on foliage and young apples but not waxy mature apples.
First- and 2nd-instar codling moth larvae were susceptible to diflubenzuron
when the compound was ingested from agar diet or apple foliage. On the diet, the LD₅₀'s for the two instars were 48.2 and 8.1 ppm, respectively. Adult codling moths dipped in or fed diflubenzuron solutions showed no marked adverse effects, although marginal reductions in fecundity or egg viability were observed.
The sensitivity of the obiiquebanded leafroller (a representative leaf-roller species) was also examined under laboratory conditions. Egg masses were insensitive to diflubenzuron at concentrations as high as 1,000 ppm. However, 100 ppm diflubenzuron proved toxic to first-instar larvae and reduced
longevity of adult moths. In field tests, diflubenzuron significantly reduced leafroller damage to apples. However, at comparable application rates (375 ppm), control was only 25% that provided by azinphos-methyl (Guthion). In contrast, against the codling moth diflubenzuron provided control equal to that of azinphos-methyl in orchards of Golden Delicious and mixed apple cultivars. The addition of Tween 20 did not enhance the efficacy of diflubenzuron. Leaf mite-counts suggested that diflubenzuron was non-toxic to predaceous mites.
The implications of these findings are discussed in terms of the potential
of diflubenzuron in the integrated control of apple pests. === Land and Food Systems, Faculty of === Graduate
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