Organic Japanese Beetle Control Methods

There ain’t no rest for the wicked! I was out dilly-dallying in the garden recently, inspecting my plants for signs of damage caused by the squash vine borer I’d spotted weeks earlier, when I caught a glimpse of something else sitting on the leaves of my pole beans. Could it be an innocent, garden-friendly beetle? Nope. I had another uninvited guest: the Japanese beetle. Told you there was no rest, and these beetles were about to find out how wicked I can be.   

What is the Japanese Beetle? 

Japanese beetles stand out because they have metallic green bodies and bronze wing covers that shimmer in the sun. They have short, clubbed antennae and tufts of white hair along their tummies. It took me all of 30 seconds to identify the bug in my copy of Susan Mulvihill’s The Vegetable Garden Pest Handbook, a book I’ve reached for many times this growing season (trust me, you need this in your life!). 

Japanese Beetles: New Kids on the Block

Kim Stoddart, author of The Climate Change Resiliant Vegetable Garden, says it’s no surprise that gardeners are finding Japanese beetles destroying their plants. She says that with changing climates, many insects are migrating to new regions. Erratic jet streams and weather patterns are widening the geographic range that these pests can invade, so if you’ve never seen them in your garden before, this could be why you do now. She groups the Japanese beetle with the fire ant, Asian citrus psyllid, and spotted lantern fly as newcomers to North America.  

Japanese Beetles and Their Targets

Adult Japanese beetles feed on ornamental plants and vegetable crops, and if you find one, there are plenty more. They feed in groups, and after checking the rest of my beans, I found four more chewing holes through the leaves. The damage causes plants to release pheromones that attract more beetles, so it’s a vicious cycle! I discovered the beetles on my beans, but you might also find them on basil, collards, corn, eggplant, lettuce, okra, peppers, soybeans, and tomatoes. So, basically, nothing is safe.  

The Life Cycle of the Japanese Beetle

The entire life cycle of the Japanese beetle takes a year. Adults emerge from the soil in June and find host plants where they can feed and mate. Females lay small clusters of eggs throughout the summer in the soil beneath turfgrass. When the eggs hatch, the larvae, which are clear white grubs with dark heads, begin to feed on grass roots, killing the lawn in the process. They mature in less than a month and move deeper down into the soil to overwinter. According to Mulvihill’s book, the beetles live about two months and lay about 60 eggs. 

Signs of Japanese Beetles

If you don’t find them sitting on your plants, you’ll know you have them if you have dead patches of lawn, skeletonized leaves, or chewed corn silks. 

Do Japanese Beetles Have Natural Predators?

Yes! Assassin bugs, birds, moles, parasitic wasps, robber flies, skunks, and tachinid flies will all feast on Japanese beetles.

Controlling a Japanese Beetle Infestation Organically

The best way to control Japanese beetles is to walk through the garden daily and observe for damage or bugs resting on the leaves. The beetles will drop from the plant as soon as you touch them, so I’ve been wearing my garden gloves and squashing them between my fingers as soon as I find them. I’ll give you fair warning: they’re crunchy. Mulvihill says hand-picking them is the best way to curb plant damage and prevent the beetle-attracting chemical signals from going out. 

She offers many other tips for controlling Japanese beetle populations, including:

• Applying beneficial nematodes, kaolin clay, neem, or pyrethrins for the beetles
• Mowing the lawn less frequently to boost lawn vigor and make it more tolerant of grub damage
• Water the lawn less often; grubs hate dry conditions

Another day, another garden pest. Ultimately, the best form of control for any uninvited guest is to inspect plants daily. The best-case scenario is you don’t find anything and simply enjoy the free therapy. Worst case, you discover you’ve got problems and take your anger out on the critter in question, which is arguably also quite therapeutic.