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Gardeners Grow Together~Week 29 July, 2021: They're Back! Controlling Japanese Beetles

Welcome to my special gardening page for those of you who like to garden yourselves! Each week, I will make suggestions as to what gardening tasks we need to do every week during the growing season. It will help keep you on track--as well as myself!

To keep things simple, I am using the year's weekly number, Week #1 through #52 (example: the week of January 1 is Week #1), instead of specific dates.

So, come on! Let's get our hands dirty!

Week 29:

How to control Japanese Beetles (sort of)


Life Cycle

Natural Controls

Milky Spore

Beneficial Nemotodes

I have to confess, the first time I saw a Japanese Beetle, I was fascinated. I thought it was the most beautiful beetle I'd ever seen, with its metallic copper wings, emerald head, and perfect tiny white dots with a black matrix running along its side. Little did I know what devastation this little beauty had in store for me. I had no idea what it was at the time.

Within a couple of days, that one beetle turned into thousands! The first things they ate were my grapes. A skeleton was all that was left of the leaves. Next they went for the woodbine (Virginia Creeper). Then they went for blossoms - my roses, zinnias and, devastatingly, my dahlias. They seemed to like the light colored flowers the most, pinks, whites and peachy. It was horrible. So, I started doing research to learn how to get rid of them.

Japanese Beetles are an invasive species, with few natural predators in this country. I started with pheromone traps. Bad idea. They worked great, I caught tens of thousands of them, but it turned out that all I was doing was attracting more of them into my garden from miles around! I didn't want to use pesticides, so my only other option was to hand pick them off the plants. Every morning, I would go out with a bucket of soapy water and knock them off the plants into the bucket when they were still a bit drowsy in the cool early morning air. It was satisfying, but not very effective with my large property. So, I had to find another solution.

The first thing I did was move the pheromone traps to the far corners of my property (at least 300 feet away), making sure I wasn't going it impact my neighbors in any way. Doing this helped to draw the insects away from my garden. Then I went looking for a biological solution.

Life Cycle of a Japanese Beetle

Japanese Beetle larva damage to turf grass

Japanese Beetles spend the majority of their lives underground as grubs. The adult beetles lay their eggs in grass turf, after the eggs hatch, they burrow down into the roots of the grass, which they feed on for 11 months until they emerge again in the summer. A heavy infestation will cause dead patches in the lawn, as well. Luckily for us, the adult beetles only are only active for about a month. Once they lay their eggs, they die. But the damage they do in that month can be very significant.

Natural Controls:

I have had good success in reducing the number of beetles by using these two biological products.

Milky Spore:

Milky Spore is a bacterial disease control that only affects Japanese Beetles, so it won't kill any beneficial larva in the soil. It comes in powder form and must be applied as directed to be effective. It also has to be reapplied every year at the right time.


Nematodes are a soil borne microscopic parasitic worm that feeds on many, many different damaging grubs and larva. They are a wonderful partner for us in the garden. They have been proven to be at least 95% effective in controlling Japanese Beetle grubs in field studies.

They come in cold packs and must be kept refrigerated until ready to use. When ready to apply, just mix with water according to directions, and just spray onto plants using a hose-end sprayer. It's that simple!

Of course these measures won't eliminate the beetle completely, but can reduce their numbers significantly. Unfortunately, the Japanese beetle is here to stay and it's up to us to control them responsibly.

Now, lets get busy!

If you have any questions, put them in the comments below!

~Lee Ann~

Valmont Valley Farm

Where Beautiful Magic is Always in Bloom

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