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Garden Plot: Insects attack! How to get rid of beetles, yellow jackets and bagworms

Friday - 7/26/2013, 1:54pm  ET

Beetle traps are magnets for the pests

WTOP Garden Editor Mike McGrath

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WASHINGTON - Mike from Beltsville, Md., writes: "Our traps are out, but we have more Japanese beetles on our roses than I have ever experienced before."

Well, that's probably because those traps are out, Mike.

Yes, it's emotionally satisfying to see those bags filled with hundreds of defoliating demons writhing away, but the math actually works against you. The lures on Japanese beetle traps are so effective that they attract four times as many beetles as your roses would alone. But traps can only capture about half of the beetles in any given area, so you're spending good money to double the number of beetles chowing down on your hybrid teas.

Either trash the traps or move them far away from any plants you wish to protect.

And keep your lawn cut high and as dry as possible -- or all of the female beetles you've invited to your yard will "plant" lots of baby grubs in your grass! (Female beetles look for wet, scalped lawns in which to lay their grubby eggs.)

Yellow jacket nests near homes must be destroyed

Jennifer in Silver Spring, Md., writes: "I've recently noticed a lot of bees near my flower bed, just steps away from my front door. They fly into a hole in the dirt and then more come out. I didn't know that honeybees nested in the ground. I'd feel bad pouring chemicals in the ground to kill them, but I'm very allergic to bee stings. Any advice?"

You wish they were bees, Jenn.

Now, if this were spring and the "bees" were flying into individual holes in the ground, they would be gentle, non-stinging native bees.

But native ground-nesting bees are "solitary." Each has its own little home. Honeybees are not native (they're from Africa), feral honeybee colonies are rare (most honeybees live in man-made hives) and honeybees never nest in the ground.

This time of year, lots of insects that look like bees coming and going from a single hole in the ground indicates a yellow jacket nest. There are hundreds of highly-aggressive stinging hornets down there, and poisonous chemicals won't destroy the nest because of how it's constructed.

Stop using that door if you can, and arrange to have someone eradicate the nest safely and effectively. Don't go near it yourself. Virtually all so-called "bee sting" deaths are actually caused by yellow jackets. These hornets like to sting and can sting repeatedly. When they sting, they inject you with a pheromone that entices other yellow jackets to come after you.

Three ways to safely destroy a yellow jacket nest

Anyone who is sting-allergic should not go near a yellow jacket nest. Children and pets should be kept away, too.

If you call a professional exterminator, make sure they will vacuum the wasps out of the ground. Sprayed pesticides of any kind are dangerous and ineffective. Yellow jackets in their nests can't be poisoned, but they can be killed.

  • One way to eliminate the danger is to drop the hose of a shop vac next to the hole late at night on a cool evening when they're not active, and then plug the machine into a grounded, approved outdoor outlet and turn it on in the morning. The workers will attack the noisy invader and be sucked inside until the nest is emptied. Leave it on until no more wasps are seen and then plug the hose up with duct tape before you turn the suction off. Then let the machine sit out in the sun for several days before disposing of the remains.

  • You can use a bug zapper the same way. Place the zapper next to the nest hole late on a cool evening, plug it into a grounded outlet and turn it on in the morning. The yellow jackets will attack the noisy intruder until it fries the last wasp.

  • You also can fill a wheelbarrow or big cooler with a load of ice and quickly dump it on top of the hole late at night. This will chill them down and temporarily trap them. Then cover the area with a tarp or sheet of thick plastic weighed down with bricks -- maybe put a big potted plant right in the middle. Don't leave any openings they can fly out of. They're not good at digging (they use old mouse holes to start their nests) and will die down there. Don't be in a hurry to remove the covering.

And again, don't waste time dumping poison down the hole. The design of the underground nest just sheds it off to the sides, and you'll probably end up being stung repeatedly.

Worst case scenario? Gypsy yellow jackets

Kirsten in Stafford, Va., has a big problem. She writes: "Yellow jackets have begun congregating on three dwarf crepe myrtles growing in front of our house. The wasp population is getting higher, we are scheduled to have new windows installed directly above these shrubs in a month, and I don't know where the nest is located. Is there anything we can do to ensure safety for the installers?"

Unless someone locates the nest -- typically a hole in the ground they fly in and out of -- your best hope is to hang a number of wasp and hornet traps in the area. These are simple devices you'll find at any hardware, home or garden store. The yellow jackets fly in but can't fly out. Over the years, I've found the best baits to be canned cat food or spoiled ham when the wasps are after protein and overripe peaches when they're after sugar.

Hang several traps containing each kind of bait in the area, and delay the installation if their numbers don't decline.

Bag those bagworms

Sheila in Leesburg writes: "I have 120 Green Giant arborvitae planted around my property as a living fence. They are five years old and 10- to 12-feet-tall. I'd always find a bagworm nest or two now and then and just pluck them off. But last year the trees got too tall for me to get the ones that were at the very tops, and now I have a full blown bagworm infestation! I can actually see the little buggers eating the tree from their bags. What can I do?!"

What you should have been doing in previous years: Spray the trees with Bt, the organic caterpillar killer. Although called "worms," these pests that nest in pinecone-like bags and prey on tasty evergreens like arborvitae are tiny caterpillars. And any caterpillar that tries to eat a plant that's been sprayed with Bt will quickly die without any harm to people, pets or the environment. Bt only affects caterpillars, and only caterpillars that eat the sprayed leaves. It's one of the most specific, and safest, pesticides known.

You'll find Bt sold online and at virtually any decent garden center under brand names like Dipel, Thuracide and Green Step. It may be called Bt or BTK. Look for "Bacillus Thuringensis" as the active ingredient. (It will not be called BTI, that's a different strain that only works to prevent mosquito larvae from breeding.)

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