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When to trim crepe myrtles

Monday - 8/18/2014, 12:40pm  ET

WASHINGTON -- As the season turns, it's time to focus on getting bugs, worms and creepy-crawlies from eating you and your plants.

'Put the pruners down and step away from the tree, sirc'

Randy in Silver Spring writes: "I need to prune some crepe myrtles because my house renters were less green-thumbed than I had hoped. They haven't been trimmed in three years and are much in need of a clip. Is September OK? Or is October better?"

I have to answer "no" and "no." Fall pruning -- especially if followed by another hard winter like our last one -- would kill these pretty plants outright. Wait until they're dormant in winter, or even better, about two weeks after they start growing again in the spring.

Randy writes back: "But ... but ... they look awful -- like wild animals. At least what I think wild animal crepe myrtles would look like. No way in the fall? Just a little trim, no whack job?"

Don't tempt me with straight lines, Randy.

Anyway, sure. Go ahead and force them to produce new growth just as winter is due to arrive -- new growth that will freeze solid and split the plants. Go ahead and sap their strength by forcing them to grow just as these southern plants are trying to go dormant for the winter. Just don't blame me when they're dead sticks this time next year.

Bottom line: The plants don't care what you want, Randy. Follow the schedule that keeps them healthy or be prepared to buy replacements.

It's the perfect time to stop beetle grubs and weeds

Lisa in Sterling writes: "Can you let us know when it's time to apply milky spore? Japanese beetles invaded and slaughtered my roses and dahlias this year and I want to eradicate the little devils. Also, when is it time for the fall feeding of corn gluten to go down? And will putting down corn gluten affect the milky spore?"

No. They are completely compatible and can be applied at the same general time of year. Just time them a week apart for good luck and to avoid any caking up.

And you're in luck, Lisa. The ideal time for both is now through mid-September, although with the corn gluten, sooner might be better than later inside that time frame. Feeding your lawn in mid-August with corn gluten meal provides a perfect fall feeding and may also inhibit the germination of weeds such as clover and dandelion. Later applications will still feed your lawn perfectly, but may not directly affect those and other cool-season weeds.

And milky spore powder (a naturally occurring soil organism that's deadly to beetle grubs, but harmless to everything else) applied to your lawn between now and mid-September will eliminate any of your Japanese beetles' grubby babies before they can do much damage to the roots of your lawn. And it will keep your lawn grub free for decades to come.

Important notes: Don't apply any other grub-killers. Milky spore needs live grubs in the soil to do its job. And it must be applied in late summer/early fall, while the soil is warm and the grubs are feeding. It doesn't have any effect if applied in the spring or early summer.

'Giant Asian bees' are actually cicada-killing wasps

John from Sterling writes: "I've got an infestation of what I identified online as giant Asian bees. They seem harmless enough but scare the dickens out of the kids. Is there a way to get rid of them without using pesticides? They bore holes in the ground and buzz around, gathering cicadas to drag into the holes, presumably to feed their young."

It's close to impossible for a layman to identify a bee or wasp just by looking on the Internet, John, but your description of their behavior clearly identifies them as neither Asian nor bees, but native American cicada-killers. These giant wasps, as you note, are harmless to us.

To avoid their return next year, make sure your lawn is never cut below 3 inches and repair any bare spots with matching seed over the next month. They won't dig through healthy turf, and will find another place in which to torment their giant noisy prey.

Be on the lookout for hungry, hungry hornworms

Jacqui in Silver Spring writes: "Can you help identify this caterpillar we found on my habanero plant?"

Yes indeed, Jacqui -- your excellent photo reveals it to be a hornworm, one of the largest of the hungry, hungry caterpillars that attack garden crops. These ravenous caterpillars normally attack tomatoes, but will happily eat pepper plants to the ground (although this one must like its food extra spicy if it's dining on a habanero).

Be sure to carefully check any other pepper plants, as well as your tomatoes, for more of the pests. Although very large, these caterpillars blend so perfectly into the plants' leaves that you often don't see them until it's obvious that large parts of the plants are missing. In fact, they eat so much that I once mistook their ravages for deer damage.

The hornworm. (Image courtesy Jacquelynne Hunter)

What's eating her?

Paula in Gainesville writes: "I desperately need your help. My backyard seems to be overrun with chiggers -- or something that causes chigger-like bites underneath clothing -- and we are hosting a backyard wedding for my daughter this September. The lawn is mowed weekly and we don't have the classic wet, brushy habitat under which chiggers are said to thrive. What can I do, short of hiring an exterminator to use lethal chemicals?"

And would the carpet of toxins that resulted replace the traditional goody-bag for your guests, Paula? "OMG. Tell the flower girl to get her shoes back on, fast."

Since I am clearly a hopeless romantic (well, hopeless anyway), I interviewed Paula at length about this unusual occurrence. Chiggers can be found anywhere in North America, but aren't typical pests in our area. Her answers clearly ruled out fleas, and the symptom areas she anguished about matched up perfectly with chigger bites. They head for "constricted areas," such as the waistbands of underwear, armpits and, yes, those other places you're thinking of right now. She also hadn't seen what's driving the family crazy -- the troublesome "babies" that cause the dreaded itch are invisible to our eyes at a very mere 1/150th of an inch long.

Chiggers are not insects. They're a type of arachnid, like ticks and mites. And they aren't bloodsuckers. But the irritants they inject into the skin drive people crazy with itching. The Ohio State University Extension Bulletin on these creatures begins, "probably no creature on earth can cause as much torment for its size than the tiny chigger."

They typically lurk in wet, weedy, brushy areas -- which she swears she doesn't have -- but the symptoms and lack of a visible foe do scream "chigger." And there's a wedding coming up, so let's not have any scratching of the bride.

Your first effort should be to spray the yard with a concentrated garlic oil product sold for outdoor mosquito control. The original is called "Garlic Barrier." You should find several brands available at large independent garden centers. If it seems to be working, spray weekly and then again the day before the wedding. The garlic odor fades in a few hours. If you want to spray it right before the wedding, serve Italian food.

If garlic oil doesn't offer enough relief, switch to a cedar oil product marketed for tick control. Garlic and cedar oils are both non-toxic and highly effective repellents -- especially against biting insects and arachnids like the dreaded chigger.

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