2014 Preliminary Results for Chemical Control of Mealybug
In 2014, AMB was monitored weekly at WSU’s Sunrise Orchards, in a conventional apple orchard with a high density of AMB. We found that second to third instar females are present and feeding on woody plant parts near buds as early as 21 March, while immature males were still in overwintering structures. Nymphs of both sexes overwinter in individual structures underneath bark. Females continued to feed under loose bark and grow rapidly throughout the spring (21 March – 24 April), then became active, dispersing to more exposed parts of the tree (cracks in the bark, old pruning scars, and at the ends of twigs), before settling to lay eggs. Emerged males were observed as early as 2 April from bark removed from infested trees. Males emerged gradually over time and were observed mating starting on 9 April, however, some could still be found in overwintering structures a week later. Crawlers emerged gradually from egg masses staring around 10 June through 16 July, and remain feeding on the underside of leaves though the fall (Figure 1).
During the 2014 growing season, WSU evaluated potential apple mealybug control materials for effectiveness and determined optimal spray timings. Weekly observations of an apple mealybug population were made to determine apple mealybug phenology during the 2014 growing season. We used this information to determine spray timings targeting certain mealybug stages (Figure 1).
Delayed dormant treatments included Lorsban+oil, Diazinon+oil, and oil targeting overwintering females. Lorsban +oil (2.0 ± 0.4 crawlers/leaf) showed a significant lower crawler population compared to the check (15.2 ± 5.2 crawlers/leaf; Figure 2), while Diazinon+oil provided some suppression.
Two systemic compounds, Ultor+oil (foliar) and Admire Pro (soil drench), were applied 14 days after petal fall. Both appeared to provide some suppression.
Finally, we applied Admire Pro (foliar), Centaur, Diazinon, and Actara to target active crawlers on leaves. The Diazinon treatment (2.1 ± 0.5 crawlers/leaf) worked surprisingly better as a crawler spray than it did at delayed-dormant. All other treatments targeting crawlers provided some suppression (Figure 2). It appears that a delayed-dormant treatment in addition to a spray targeting active crawlers may give the best results. Note that application timings will differ for grape mealybug control due to lifecycle differences. WSU will continue its studies on apple and grape mealybug control during the 2015 growing season.