Beating Back Beetles

It’s July, and the crunchy, metallic adult Japanese beetles are ramping up their feeding frenzy. So what can you do? Unfortunately, the Japanese beetle has few natural enemies, as most birds stay clear of them and our local mammals will feast only on the grubs. So it’s up to us.

For purists, there is hand-picking, and this is probably the best method of control for just small outbreaks of JBs. The beetles are simply picked off the plant (wear gloves if you’re squeamish) and dropped into a bag or jar containing a bit of salad oil that will keep them from flying away, or a container of soapy water. There are also vacuum devices that can be used to suck them up, and I suppose a small shop vac would work as well.For those wanting to use a spray, there are several choices. When used early in the day, insecticides containing pyrethrin (some will also have fatty acids) will quickly knock down the beetles and usually kill them. This is a reliable organic control and you can also try products that contain spinosad, which is a new organic insecticide. It must be ingested by the insect, so it can take a couple of days to be effective. Neem oil is also a possibility, as it’s said to have a repellent effect and also disrupts the eating and reproductive abilities of the beetles, although my trials for several years have been inconclusive. The next step would be a chemical insecticide that you can find on the garden center shelf, the most effective being Sevin. I would suggest using Sevin only as a last resort or if you have a really serious problem, because this is a non-selective insecticide that will kill not only the beetles but many beneficials as well—and it’s highly toxic to bees and fish. Unlike the organics, though, Sevin can be effective for several days.

Another option for those not wanting to use chemicals are beneficial nematodes (Heterorhabditis spp seem to be most effective), which are tiny microscopic worms that feed on the young grubs. Remember, though, this will not help you at all with this year’s crop of adult beetles. Nematodes are best applied when the soil is warm and moist, and while they can be effective, all the feedback I’ve been getting for years is that if not applied properly the results can be spotty at best. It’s also pointless to apply the nematodes when the grubs are not present in the soil … like now. Another natural approach is the use of milky spore (Bacillus popilliae), which is a bacteria that can also kill the grubs. However, this can take years, as the bacterial population in the soil needs to build up over time. In addition, milky spore will not eradicate a Japanese beetle population and is generally thought of as only a “population suppressant” that is often seen as not cost-effective.For those who want to stay away from chemicals but have JB problems, a combination of hand-picking along with nematode applications and organic sprays may be the way to go.

Years ago, traps were very popular for “catching” beetles, and people swore by them. You’d buy a kit that contained a yellow plastic baffle, a plastic bag that hung from the baffle and a sex lure/scent attractant that stuck onto the baffle. The sex lure is a pheromone or sex hormone that the female beetle uses to attract the male. The scent lure is called geraniol and is a combination of rose and geranium scents. The idea is to hang the baffle with the lures attached and the plastic bag dangling below and put it in your yard or garden. The lures will attract the beetles, they hit the baffle and drop into the bag. And it worked … kind of. In no time your bag was full of beetles and you had to empty it often, so everyone assumed that the beetles were all going to the traps, end of story. But the story goes on. Subsequent research has shown that less than half of the of the attracted beetles ended up in the bag and that the traps actually attract beetles from several thousand feet downwind, where the “scents” are picked up.

But, according to Dr. David Shetlar in the department of entomology at Ohio State University, “Recent data indicate that these traps do not significantly reduce grub populations and in some cases may actually contribute to increased foliar plant damage. There has been no correlation between trap captures and reductions in white grub populations in surrounding turfgrass areas.”

So, if you placed your trap in the wrong location you’d actually be attracting all of your neighbor’s Japanese beetles onto your property, where only maybe 40 percent of them would end up in the trap’s bag. The other 60 percent are having wild sex and making sure lots of their kiddies are around to torment you, your garden and lawn next year.

Finally, there is Merit (imidacloprid). This is an insecticide that has been touted as being very safe, but there are now numerous doubters. Since traces of this insecticide began to show up in Long Island’s water table, the State Department of Environmental Conservation has restricted its use to trained applicators (as in, professional lawn care companies). There is little question that Merit is highly effective when it’s applied properly (it goes down in late spring to early summer, and it kills the next generation of grubs that develop in late summer, but not this summer’s feeding beetle population). I suspect that Merit applications every three or four years may give good results as opposed to annual applications, which are common and potentially unnecessary.

What do I use? At this time of the year I try to “drop” as many of the beetles into a small can of soapy water (about 5 to 8 drops of Joy in a quart of water) as I can, and the beetles die in about 5 minutes in this brew. The ones I can’t reach I spray with a pyrethrin that has PPB or PPO (pypernol butoxide) in it as a synergist. I try to spray before 10 on sunny days because the heat of the day can make the beetles unresponsive to the spray and pyrethrin does not work well in high temperatures. I only have one place in my garden where JBs are an issue though … on my rose of sharon plants. So, you have options and there’s a way to control these insects for every type of gardener. Choose your control wisely and consider all the alternatives. Also remember that putting a rose garden right next to a nice lush lawn is just about the best combination of food and habitat that you can offer these beetles and guarantee problems for years to come. Keep growing.