At this time of year, you are probably seeing those tell-tale shredded flowers and skeletonized leaves. Upon closer inspection, it’s confirmed — the Japanese Beetles (Popillia japonica) are back and busy eating and mating in preparation for next year’s invasion. And you know that when you see one or two, you’ll likely see hundreds in the next few days.
Consider while you engage in warfare with this year’s crop of beetles what you can do to prevent them in years ahead by using their natural enemies instead of traps and pesticides. Birds, spiders, and predator insects can kill many more Japanese beetles you will be able to even with the most extensive chemical countermeasures. If you haven’t laid down broad-spectrum insecticides (organophosphate and carbamate insecticides like chlorpyrifos–Lorsban and methomyl–Lannate), you should have plenty of beneficial insects living in your yard and in your soil. As for your chemical options, you can download UTK’s brochure here.
Japanese beetles can be found in four stages (phases): as eggs, larvae (grubs), pupa and adult beetles. The key to using natural Japanese Beetle control is to attract, implant and keep natural beetle enemies in your yard and garden at each stage of beetle development.
Eggs and Grubs: Using an Effective Ground Assault
Eggs are a particularly vulnerable development stage and natural predators can play a major role in cutting down this year’s hatch. Spiders and ants will consume large numbers of beetle eggs in the soil even before they hatch.
While you might not be immediately aware of what’s going on below the surface, Japanese beetle and other white beetle grubs (June beetles, chafers) are busy feeding on grass and other plant roots. The grubs hatch from buried eggs usually in the summer and immediately begin feeding on available roots and other plant matter near the surface. As the climate gets colder, the grubs may burrow deeper and become inactive. In general, the heaviest root damage usually occurs in early spring when the grubs move toward the surface again and fatten up in preparation for their emergence as pupae.
Within the soil, there is a very deadly white grub predator– a microscopic roundworm also known as a “nematode.” Entomapathogenic nematodes live in the soil and feed on the bacteria deadly to the beetle grubs. The nematodes penetrate the grub, injecting it with the bacteria that will infect the grub and eventually kill it. One of the most effective nematode varieties is Heterorhabditis bacteriophora and is commercially available under a number of labels (Heteromask, NemaSeek, Terranem).
Parasitic wasps like spring tiphia wasp (Tiphia vernalis) and the beetle’s natural enemies like the Istocheta aldrichi fly are another grub control measure. The tiphia wasp was originally released in northeastern US in between 1925-7 and has successfully spread throughout the US in pursuit of Japanese Beetle infestations ever since. Both predators implant grubs with their eggs. Upon hatching, the wasp and fly larvae feed on the grub, killing it. Both predators also feed on aphids, a side benefit. Other insects that feed on grubs include Assassin bugs, ground beetles, spined soldier bugs, and wheel bugs.
Aerial Assault – Birds
Among bird predators, Starlings are the best known beetle-eaters, eating both the grubs and adult beetles. Other birds known to eat grubs are robins, crows, grackles, catbirds, sparrows, bobwhites, blue jays, eastern kingbirds, woodpeckers and purple martins. You can often see birds pecking at your lawn — they may be hunting — and eating — beetle grubs among other garden and lawn pests.
By the time the adults have emerged with their protective shells, it becomes harder to control their numbers. Some birds like Starlings are known to eat the adult beetle although if truth be told, I have never witnessed a bird eating a Japanese Beetle. Other area birds reputed to be Japanese Beetle eaters include robins, cardinals and catbirds.
Feed Birds Year Round
Next to beneficial insects, songbirds consume the most pest insects in your yard and the best way to attract birds is to provide them with year round food (bird feeders), water, and shelter. An excellent review of attracting garden pest eating birds can be found at National Wildlife Federation’s eNature website.
Mow The Lawn Properly
Japanese beetles prefer to lay their eggs in turf grass that is short, avoiding grass that is more than 2 inches high. Tall grass harbors natural beetle egg predators like ground spiders and ants. And, cool season turf like fescue should be maintained at a higher length regardless for many other good reasons, so consider this one more reason for keeping your lawn mower setting at around 3 to 4 inches.
Plant Resistant Varieties
Another strategy is to use plants that are not on the Japanese Beetle’s preferred eating list. The UTK publication cited above provides examples of Tennessee suitable shrubs and plants that are not as susceptible to Japanese Beetle attacks.