Battling Flea Beetles with a Brand New Bt

Q. Amy in Knoxville, TN writes: “I remember hearing on a previous show that a new, safe treatment was available for flea beetles. I have had problems for years with those shiny black beetles eating my Rudbeckia and I’m determined to deal with them this year. Could you please remind me of the name of the product?”

A. I suspect that Amy may have heard me talk about BT galleria, the most recent type of Bt to enter the market, often referred to simply as BTG.

Bt Background: The original strain of Bt (which organic growers depend on to control pest caterpillars), is Bt kurstaki. Discovered over a century ago, this naturally occurring soil organism is deadly to caterpillars that eat plant parts sprayed with a solution of the bio-pesticide, which was then just called ‘Bt, because no other strains of Bacillus Thurengensis had yet been found that would help control pests. It is still often referred to simply as Bt.

But other helpful strains have since been discovered, like BTI (the ‘I’ stands for the subspecies israelensis, so named because it was discovered in Israel). BTI products are sold in the form of granules and dunks shaped like small donuts. Added to standing water, BTI prevents mosquito larva from maturing into biting adults. Female mosquitoes only lay their eggs in water, so treating standing water with BTI is much more effective than trying to kill adult mosquitoes, as it prevents those adults from ever appearing.

Just be aware that the original form of Bt (sold under brand names like Dipel and Green Step II ONLY works on caterpillars; and those caterpillars must chew on plant parts that have been sprayed with Bt for it to be effective. It is harmless to everything that is not a caterpillar. BTI only works on mosquito larva and nothing else.

Birds, dogs, ladybugs, toads, pollinators, beneficial and even non-beneficial insects can drink BTI treated water without harm. Non-caterpillar pests can chew on Bt sprayed leaves without harm. All of the Bt strains are very specific; they only affect the designated target.

I emphasize this because many people use the words interchangeably and are surprised when basic Bt doesn’t stop mosquito larva. Remember: Bt for caterpillars; BTI for mosquitoes.

(PS: don’t spray Bt on ‘host plants’ that the larval forms of desired butterfly species feed on, like milkweed and parsley.)

Which finally brings me back to those pesky flea beetles. As long-time listeners know, I began extolling the virtues of a ‘new’ strain of Bt a few years back: Bt galleria, which was found to be very effective against Japanese Beetles. Spray it on plants under Japanese beetle attack and any beetles that munch on the sprayed leaves will stop feeding and soon die. It is equally effective on other {quote} ‘scarab beetles”, including the Oriental beetles that attack the same plants in the same way as Japanese beetles but do their dirty work at night.

Gardens Alive was the first company to release it publicly, under the [ahem] name “Beetle-Jus”, both in a spray form for adult beetles and as a drench [powder?] to prevent their lawn-destroying grubs from reaching adult form. It is also listed as being effective against other kinds of beetles, including the Emerald Ash Borer; and all sorts of weevils as well.

One of the insects EPA testing found BTG to be effective against were flea beetles. So, to keep it simple, spraying BTG on your rudbeckia or other plants under flea beetle attack should make any flea beetles feeding on the leaves stop eating and soon die.

But while researching this topic WAY too much, I stumbled upon a new sub-strain of BTG that is specific to flea beetles called Bt HAN055. It was developed in China and only recently became available to the American market. I quote from its entry in ‘Google Patents’ (yes, there is such a site): “A strain of Bacillus thuringiensis HAN055 with high virulence to Flea beetle was isolated, and the preparation WP-HAN055 made from this strain has a significant control effect on Flea beetles.”

I’m not sure if it’s available in the US yet, but as soon as I find a source I’ll let you know. In the meantime, in addition to “Beetle-jus” (aka Bt galleria), another proven organic control for flea beetles (and a variety of other pests) is Beauveria (‘bo-ve-ah’) bassiana, a bio-pesticide that’s been around for awhile, but seems to fly under the home gardening radar. 

It works by attacking insects with a fungus that weakens and destroys them. I was able to find it for sale from several suppliers; Mycotrol seems to be the most common brand name.

In addition, spraying the plants with Neem oil has been shown to repel flea beetles; and dusting the beetles directly with diatomaceous earth (often just called ‘DE’; a naturally-occurring mined substance composed of the fossilized remains of ancient sea creatures known as diatoms) will dehydrate them.

And finally, some species of beneficial nematodes take care of the pests in their early larval stages underground. Gardens Alive sells an ‘all-purpose’ species known as Steinernema feltiae under the name “Garden Army Multi-Purpose Nematodes” that takes care of a number of different pests in their larval stages underground, including flea beetles. You can also search “nematodes that attack flea beetles” for any other sources that may be out there. Just be sure the species is identified as useful against flea beetles.

This is a lot to take in, so for more information; and especially to make sure you get the right stuff, I’m listing some references and citations below. Happy Hunting!

https://patents.google.com/patent/CN108070534B/en

https://news.agropages.com/News/Detail-45299.htm