Growing Concerns 521: Japanese beetles, beetle bags

Early Summer!

Japanese beetles are terrible but not the only pest of roses


Dear Janet,

Last year I duked it out with Japanese beetles from June until fall. They will eat my rose buds from the inside out, and they literally covered my bushes before I could even cut buds to bring them inside to save them!

So I tried a "beetle bag" and even though I followed instructions (place bag down-wind, etc.) I still had problems. Not to mention that I was catching probably hundreds every day in those bags!

I cannot understand why I have such a problem. Others who live 30 to 60 minutes away have no trouble with these pests. Any ideas? I hate to go through it again this summer.


Dear D.,

Japanese beetles are obnoxious, but you may be laying too much at their feet. For instance, it was probably rose slug that harassed your roses in June, eating buds from the inside. Japanese beetles don't operate that way and they favor soft, ripe tissues -- flower petals and leaves -- over green, crunchy unopened buds.

They don't eat all summer, either, but start in late June or early July, peaking in August. Perhaps you've locked in one image of last summer and superimposed it on the whole growing season. That's often done with flowers. People say "it bloomed all summer!" of a favorite plant, even though an impartial observer will tell you that cleome, dahlia, cosmos, salvia or threadleaf coreopsis did not begin to flower until July.

What works against Japanese beetle is not a trick but a tactic that can beat any pest -- anticipate its arrival. Stop it before it gets started.

In this respect, Japanese beetles are easy targets. They all emerge over short period each summer and that time is predictable. When snowball hydrangea flowers are turning from green to white, look for these beetles to dig up from under the sod that's been nurturing them as grubs since last summer.

Look for them on their favorite plants. Here, too, they are easy to predict since they favor the same roses, raspberries, linden trees, Harry Lauder's walking sticks, hollyhocks, etc. each year. Hunt them early in the day when they are moving slowly. Knock them into a bucket of soapy water, spray them with an insecticide, or pick and crush them. At the start of beetle season you might cover the plants they like best with floating row cover -- that lightweight cloth sold for frost protection. The beetles are still drawn to the plant's smell but become stark targets against the white fabric.

In the case of Japanese beetles early action is even more important than with other insects since content, well fed Japanese beetles emit pheromones -- chemical attractants -- that can draw others of their kind from half mile away. The more beetles that land and feed in your yard, the more others they "call in." Stop the first wave and many other beetles will go elsewhere.

Your beetle bags are probably traps baited with pheromone. Throw them away! The best use for scent-traps, which are custom-made for each type of insect, is to detect when an insect appears each year. Given that information, other methods of pest management can be timed for most impact. Once target insects appear in the trap, the trap is put away. To leave it out is to invite more trouble.

Marketers, not pest management experts, promote "beetle bags." Horticulturists joke about finding a fall guy to put up a beetle bag, at least a quarter mile away, so all the beetles will go there!

Why do you have trouble with this pest while other people don't? "Other people" beg to differ.  Like all insects, it proliferates in some localities. Large areas of turf can support lots of the grubs so people near athletic fields and golf courses may see more Japanese beetle damage than those near forested parks. Sometimes wind pushes more insects to the east than the west as they emerge and begin to fly, or the smell of favorite foods lures them one way rather than another.


Short report

No time to pluck every weed from the garden?

Remove weeds closest to the bases of desirable plants. Then put a few inches of mulch on the spaces between plants, right on top of the weeds. Or spread a sheet of newspaper plus an inch of mulch. Seedling weeds will die and larger survivors will be easy to pluck later from the loose, moist soil beneath a mulch.


Green thumbs up

to garden center employees whose most demanding season seemed to have no end this year as rain and cold extended our shopping and planting. All my best to those who keep smiling and serving, even when so steeped in the season that they inadvertently address a greeting card to "Rudbeckia" rather than the intended "Rebecca!" 


Green thumbs down

to giving up on the growing season if you didn't get your garden planted on schedule by Memorial Day. We still should have at least 70 frost-free growing days, and perhaps as many as 100. That's plenty of time to see tomatoes bear fruit or begonias fill in, even if they were first planted in late June! 

Originally published 6/21/03