Garden Plot: Controlling grubs doesn’t always beat the beetles

Controlling Grubs Doesn’t Always Beat the Beetles

Anne Marie in Williamsburg is grateful for last week’s non-toxic grub control advice but writes: “Not all of my neighbors use the milky spore grub treatment you spoke about on their lawns, and our homes are close together. What can I do to protect my crepe myrtles? Their flowers were eaten by the adult beetles in a week this season!”

Japanese beetles are unusual in that they are pestiferous in both the adult and larval stages, Anne Marie. Milky spore powder and the grub killing form of the new BTG (sold by the mail order form, Gardens Alive as “GrubHalt”) can prevent baby grubs from eating the roots of lawns and other plants, but you are correct — they can’t prevent adult beetles from flying into your garden from nearby properties.

That’s where another version of BTG comes into play.

BTG: One version for Greasy Grubs, One for Bad Beetles 

Anne Marie is correct — eliminating lawn grubs does not prevent adult beetles from flying over to your house to feast. But there’s a brand new answer to those rose-ravaging monsters: BTG.

BTG is the newest strain of Bt to be released to the public. Like the older strains, BTG is a naturally occurring soil organism that is harmless to people, pets, bees and birds. But if you spray the version formulated to work on adults on a plant under attack, any beetles eating the plant will die (that includes scarab beetle cousins like the Asiatic beetle and rose chafer).

The mail order firm Gardens Alive sells this “adult” version of BTG as “BeetleJus”, and it may be available at retail under other brand names. Make sure you have it on hand when the first beetles start feeding next season and un-ravaged your plants should be!

Bt 101

We’ve been talking about the newest strain of Bt a lot this summer, so let’s drop back and take a close look at the entire Bt family. “Bt” stands for Bacillus Thuringensis; a large family of soil-dwelling organisms (the first of which was discovered in Thurin, Germany).

  • The first to be commercially developed was BTK, better known under the brand names Dipel and Thuracide. Spray BTK on a plant under caterpillar attack, and the caterpillars will quickly die. (Note: This original strain, developed a century ago, is often referred to simply as ‘Bt’.)
  • Then came BTI, which you’ve all seen for sale in the form of donut-shaped dunks on hanging cards in hardware and home stores. Applied to standing water, BTI prevents mosquito eggs from developing into biting adults. (Here’s a link to Summit, the company best known for producing BTI products.)
  • Two formulations are available:
    1. BTI granules provide a strong initial knock-down but last only for a week to ten days.
    2. Larger forms compressed into the shape of “dunks” and briquettes are for longer-term (30-day) control in large bodies of water.
  • New to the family is BTG, which has only become available over the past few years. BTG is also available in two forms: a spray that kills plant-eating beetles (the biggest brand name is “BeetleJus” from Gardens Alive), and another form that kills grubs underground (GA calls their version “Grubhalt”).

Important note: All of the Bts are very pest specific. BTK only affects caterpillars that chew on the sprayed leaves of the plant. BTI only prevents mosquitoes and gnats from breeding in standing water. And BTK only affects beetles (and their grub stage) and pest weevils. None of the Bts pose any danger to people, pets, fish, bees or other good things.

Class dismissed!

Zoysia Grass Requires a Different Kind of Care

Tammy in Alexandria writes: “I have a question about the care of zoysia grass. The yard was established over 40 years ago and looks like it needs some TLC. Could you please provide me with info pertaining to the care and feeding of our zoysia yard?”

My pleasure, Tammy!

Zoysia is a warm-season grass originally from Asia. It goes tan and dormant over the winter, greens up for the summer, and its care is basically the opposite of what you’d do for fescue or bluegrass.

Do nothing now; your zoysia is preparing to go dormant and will soon lose its green color.

When it begins to green up in the spring, give it a gentle feeding of corn gluten meal or a bagged organic lawn fertilizer.

When it’s fully green, do a de-thatching. Zoysia is prone to developing large amounts of thatch and really benefits from some of this dead stuff being removed. You can either buy a specialized de-thatching rake (they make ones specifically designed for zoysia) and rake out the old dead stolons yourself, or you can hire a powerized dethatching machine.

When this chore is finished, give the grass another gentle feeding and it should look great. Do not feed in the fall or over winter.

Oh, and zoysia should be cut at two inches high — that’s an inch shorter than recommended for fescue and bluegrass.

Gnat Control

Patrick in West Springfield writes: “Every day at around five o’clock, tiny black insects descend upon our back yard and patio leaving us with small bites. Then they disappear in an hour or so. We do have a pool and do our best to keep standing water from gathering. Any ideas on how to reclaim our yard in the evenings?”

Yes, these little black gnats are super-annoying.

  • If you’re just sitting around outside, a strong oscillating fan can keep your table gnat-free (and keep you a little cooler).
  • Natural repellents that contain lemon eucalyptus as the active ingredient work as well or better than the chemical repellent DEET. (And they’re a darned sight safer!)
  • Next season, use BTI granules and dunks to treat any standing water you can’t remove. And set BTI traps outside to cut their numbers down before they can begin breeding in full force.

Mike McGrath was Editor-in-Chief of ORGANIC GARDENING magazine from 1990 through 1997. He has been the host of the nationally syndicated Public Radio show “You Bet Your Garden” since 1998 and Garden Editor for WTOP since 1999. Send him your garden or pest control questions at

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