When your life is a frantic sprint to manage family, home and job, a comfortable bench beneath a Japanese maple (Acer palmatum) can be the perfect spot to relax. Zen garden staples, compact Japanese maples bring sharply sculpted leaves, eye-catching red seedpods and vivid fall color to yards in U.S. Department of Agriculture plant hardiness zones 5 through 8. Their striking foliage attracts equally striking -- and occasionally damaging -- striped bugs.
Green-Striped Mapleworm Moths
Green-striped mapleworm moths fluttering around Japanese maples in the late spring or midsummer at dusk make a pretty picture, with their yellow-striped, pink forewings and fuzzy yellow bodies. While their visits may provide a wonderful photo op, the moths' only intention is to deposit masses of light green eggs on the backs of the maples' leaves. Within 10 days, those eggs produce voracious, foliage-munching caterpillars. Large numbers of these redheaded, green-striped yellow eating machines may strip a maple of its leaves in the month they feed on it before they move to the soil to pupate.
In years of heavy mapleworm feeding, you may need to step in to save your Japanese maples. Instead of using toxic chemical pesticides, spray the trees with kid-, pet- and plant-safe Bacillus thuringiensis var. kurstaki microbes. Start checking in May for light green eggs on the backs of the leaves. When they begin hatching, saturate the foliage with a garden sprayer containing 1 to 2 teaspoons -- or the manufacturer's specified amount -- of wettable Bt powder per 1 gallon of soft water. Continue spraying with fresh batches of solution every three or four days until the eggs are gone. Bt bacteria disrupt the young caterpillars' digestion systems so they eventually starve. Spraying on a cloudy day or at dusk protects the UV-sensitive microbes.
You'll recognize winged, flat, black adult boxelder bugs from their red eyes and the orange-red pinstripes outlining the area just above their wings. Their red-bodied, black-legged nymphs’ gray or black wings develop red veins as they mature. After hatching in spring from yellow eggs deposited in bark crevices, the nymphs feed on Japanese maples' leaf sap until midsummer, when they mate. Their offspring head for protected overwintering spots, such as tree hollows, rock and wood piles or building foundations and interiors. If you're in a mild-winter climate, you may find the bugs congregating on your' home's south or west side on sunny winter days.
Managing Boxelder Bugs
Don't be concerned if you spot boxelder bugs feeding on your Japanese maples, because they seldom cause serious damage. The real problem comes if the bugs begin invading your home to escape the winter cold. To prevent that, eliminate the pests by washing them from the maples' trunks with a strong spray of water. Boxelder bugs drown easily, and the non-toxic insecticidal soaps or horticultural oils used to remove them from other trees aren't safe for Japanese maples.