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Adult Japanese beetles do unsightly damage in the garden, feeding on the leaves and blooms of about 270 different species of plants.
Photo by William Fountain, University of Kentucky, Bugwood.org
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Three species of white grubs that commonly damage lawns include (left to right) the Japanese beetle, the European chafer and the June beetle.
Photo by David Cappaert, Bugwood.org
Pop quiz: What do Japanese beetles, Asian tiger mosquitoes and red imported fire ants have in common? Answer: They’re not supposed to be here! All these insects are non-native invasive species, brought here accidently in shipments of internationally traded products. And all of them cause harm in the landscape.
One pest we’ve battled for a long time is Japanese beetles. Summertime brings the familiar sight of these bugs voraciously feeding on the leaves and blooms of about 270 different species of trees, shrubs and flowers. Although the damage their feeding leaves behind is unsightly, it rarely causes severe harm to healthy plants.
The real damage from Japanese beetles often goes unseen. Immature beetles, or larvae called white grubs, are considered the number-one insect pest of lawns. They feed on grass roots below ground. Heavy infestations will cause a severe decline of your turfgrass.
You can manage the aboveground feeding of adult Japanese beetles with a number of insecticides. I prefer to handpick them from leaves into a bucket of soapy water. This is easy when populations aren’t too high. Songbirds will also help; they’re fond of the multicolored beetles. If populations are high, or there’s more leaf damage than you can tolerate, buy an insecticide labeled for Japanese beetle control at your lawn-and-garden center.
Many people like Japanese beetle traps, which use attractants to lure adults to their demise. Sounds good in theory, right? But research has proven that the lures are so effective, they actually attract more beetles to your landscape. Plus, not all beetles find their way into the trap. As a result, you end up with more beetles and more damage than if you hadn’t spent $5.99 on a trap. You’re better off if the traps are located at your neighbor’s house, three doors down!
While Japanese beetle adults harm plants for only a few weeks in summer, beetle larvae (grubs) damage grass roots much of the year. The damage caused by white grubs (including other beetle species, such as Southern masked chafer and May and June beetles) is often misdiagnosed as disease, lack of water or poor fertility. White grubs are also a favorite snack of several animals, such as skunks, moles and armadillos, which will destroy a grub-infested lawn by digging or tunneling to reach the tasty morsels.
Check your lawn periodically for grubs. Simply peel back a square foot of sod and examine its root zone for white, C-shaped grubs. If you see 10 or more grubs per square foot, treatment is necessary. Fewer than 10 isn’t likely to cause serious harm to a healthy lawn.
There are two basic strategies for managing grubs. One is to use a biological product called Milky Spore. This is a bacterial disease that infects and kills Japanese beetle grubs. Once this disease is established in a lawn, it can effectively manage grubs for 20 to 30 years. But it takes two to three years to achieve complete control. This organic-approved product, available at lawn-and-garden centers, is applied as a powder. Follow the product label for application instructions.
The second strategy uses insecticides. During summer, offending beetles lay eggs in the sod; these hatch and begin feeding on grass roots. June through July applications of preventive grub-control products, with active ingredients imidacloprid, dinotefuran, thiamethoxam, clothianidin or chlorantraniloprole, are most effective, because they kill grubs as they hatch and begin feeding near the surface. Many grub-management products work equally well on multiple species of white grubs. Some are labeled as “grub control”; others as more broad-spectrum “lawn insect control.” For heavy infestations, look for curative insecticides with the active ingredient trichlorfon, and apply late summer through early fall.
With some careful grub management, you can keep these garden invaders at bay.
S. CORY TANNER is an area horticulture agent for Clemson Extension based in Greenville County. Contact him at shannt@clemson.edu.