In the past, mealybugs haven’t posed a significant problem for cherry growers because they don’t cause direct damage to cherries, but because apple and grape mealybugs are vectors for little cherry virus 2, researchers are looking for ways to combat them.
Control is challenging because mealybugs differ in their life cycles: The apple mealybug has just one generation per year, while the grape mealybug has at least two, which is an important consideration when timing control methods, said Dr. Andrea Bixby-Brosi, postdoctoral research assistant with Washington State University’s Tree Fruit Research and Extension Center.
With grape mealybugs, she said, “At some point in the summer, you could have eggs, nymphs, crawlers and adults on the same tree.”
Bixby-Brosi and a team of researchers tracked the life cycle of apple mealybugs at WSU’s Sunrise Orchard between Wenatchee and Quincy in 2014 and 2015.
They found that females were emerging from overwintering sites in midspring, followed by males. Egg masses were laid around June, and crawlers emerged during that month.
“It’s interesting to see the difference between 2014 and 2015,” Bixby-Brosi said. “We had a hot spring and summer in 2015, and everything emerged about a month ahead of what it did the year before. That’s another thing to take into consideration when managing these pests.”
The researchers tested several approaches to controlling the mealybugs: delayed dormant pesticide applications to intercept overwintering females; systemic petal fall applications to target crawlers; and foliar summer sprays timed when 70 percent of the crawlers are estimated to have emerged.
In the 2014 trial, a combination of Lorsban (chlorpyrifos) and oil spray was found to be most effective at the delayed-dormant stage. Diazinon worked best at controlling the newly hatched crawlers later in the summer.
Researchers tested again in 2015 and found the same results, with one addition: A combination of Centaur (buprofezin) and oil also was effective at the delayed-dormant stage.
For grape mealybugs, systemic compounds, Admire Pro (imidacloprid, a soil drench) and Ultor (spirotetramat) and oil, applied 14 days after petal fall showed the best results.
Research continues this year into possible chemical-control recommendation for organic growers, as well as research into natural mealybug enemies in orchards.
– by Shannon Dininny