Japanese beetle

Just who are these infamous little grubs that have the ability to reap such levels of fear in the minds of the homeowner? To say their reputation precedes them is an understatement.

Actually they haven’t quite arrived yet or at least they haven’t in their most voracious stage: as grubs. That, my friends, is the good news. The bad news is they’re here. It’s just that you see them in a different form. Right now chances are many of you are doing battle with Japanese beetles (some of you more than others) and in doing so, you are actually combating the adult stage of the grub that will soon be gnawing on the roots of your grass plants.

However, before we venture further, let me say that there is another beetle, the European Chafer, whose grub can also wreak havoc on turf. Since distinguishing between the two grubs may be difficult for the homeowner, I will refer to the Japanese beetle for simplicity.

Also fondly known as Popillia japonica, this beetle is native to Japan where it isn’t considered a pest because of natural predators. It’s believed the beetle hopped a ride to the United States in shipment of Iris bulbs back in 1912 well before import inspections were required.

By 1916, the first population was discovered in a nursery in New Jersey.

The Japanese beetle is a small, oval shaped beetle roughly a quarter inch in length and width, emerging from the soil in early June. Its body is metallic green, a dead giveaway when identifying this pest. (The European chafer, by contrast, is a coppery brown in color.) It feeds on many different plants by devouring their leaves. A few of their favorites include roses, hollyhocks, raspberries, apple and grapes. They are also attracted to a variety of weeds, hence another reason to try to keep your gardens weed free.

If you can control the adult beetle stage, you can reduce the larval grub stage. The best approach to controlling the beetle is simply to take a coffee can, put some warm soapy water in it, and flick them in (this is effective for potato beetles, too). Hunt them in the early morning or evening when they are sluggish.

Can you spray? Yes, but remember to do so in the evening after the bees have gone back to their nest for the night. They have enough problems, and do so much good for humans they’re worth taking care to preserve. Also keep in mind that if you spray fruits or vegetables you will need to wait some time before harvesting.

Two pesticides are recommended for control: nonorganic is Carbaryl, found in Sevin; the organic alternative is Pyrethrum, which is found in Rotenone. Read and follow all label directions.

Ah, but what about beetle traps? Let me say this: If you hang one, they will come, all of them. The traps work by attracting the beetles with natural pheromones and floral lures.

They not only attract the beetles in your yard, but those in your neighbors’ yards, too. Before you know it, you are Hotel Japanese Beetle and on days when your traps are brimming over, the excess beetles simply find food elsewhere . . . in your yard. Use these traps wisely: if your yard is isolated so the attraction will simply be resident beetles, fine; if all your neighbors agree to put up traps and take care of them (they overload quickly — I’ve seen the bags burst from the weight — so empty daily), great.

Right about now the adult beetles are beginning to mate. The females will lay eggs, the eggs will hatch and the grub will take shape. It’ll grow to about an inch by autumn’s end; going through three “instars” or life cycles. As the colder soil temperatures creep in, the grub creeps deep into the soil to wait out winter, emerging next June as the Japanese beetle.

So now what do you do to control the grubs?

First and foremost, don’t just assume you have grubs. Cornell recommends you scout your lawn for activity. Because they are root feeders, you’ll need to dig down to the root zone. With a shovel remove a 1-square foot area of sod; it’s easiest if you cut out 3 sides of the square and roll the flap back over the side still intact. Count the number of grubs; less than five grubs is an acceptable population and there is no reason to treat. Replace the sod, water and then move over 10 feet and repeat the test, continuing at 10-foot intervals.

Lawns are natural homes for grubs; that’s just nature. It’s when the population per square foot reaches 8 to 10 grubs that Cornell indicates treatment may be necessary.

For those with healthy, dense lawns, even this higher threshold can be tolerated, letting Mother Nature take care of the natural balance. Others may choose to treat. If your lawn has problems, the grubs alone may not be at fault, so treatment is not a no-brainer.

If you do treat, treat only those sections that have a population that meets the 8-to-10 grub requirement. If you choose to treat and you have a well, be particularly cautious to not contaminate your water (again, follow directions on the products you use).

Any application must be watered in thoroughly to be activated and to get the control into the root zone where the grubs can ingest it when actively feeding. It’s important that applications are made at the right time; again, so the grubs are present and ready to do their job during the active feeding stage. Remember, grubs are very inactive in late fall as well as spring, so applications made during those times are not recommended.

What are the control options? The most promising biological control is beneficial nematodes, which you can buy through the company Gardens Alive at their Web site www.gardensalive.com.

Nematodes are tiny worms that enter the bodies of grub larvae that live in the soil, infect them and kill them. The beneficial varieties do not harm people, pets, plants or beneficial insects. They arrive by the millions on a small sponge that you keep in the refrigerator until you intend to use them. You then soak the sponge in a bucket and water the nematodes into the lawn or garden.

They are applied when soil temperature is about 60 degrees, usually in the spring or fall. Sunlight kills them, so apply only early in the morning or late in the evening. The population will take some time to reach an effective control level.

Another control, no longer recommended due to its inability to survive winter temperatures here, is Milky Spore, a bacterial disease.

As for chemical controls, these must be applied now in order to be in place when grubs are feeding.

Nancy O’Donnell is a nursery owner from Schaghticoke, N.Y.