A Few Tips To Protect Gardens From The Japanese Beetle

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Growing along my front porch, a Virginia creeper rises up from the ground 10 feet below. It twists around 6×6-inch porch support, and once reaching the railing, branches are trained left and right to provide the south-facing porch deck some protective shade during the summer.

Honestly, the plant isn’t very spectacular or showy. Once the leaves emerge from their buds in May, small, inconspicuous clusters of greenish flowers follow in June. These mature into dark blue, grape-like berries in late summer that last into fall and are relished by house wrens, robins, and other birds that dare to light close to the house for an autumn feast.

Beyond that, at the bottom of the hill, is our vegetable garden. It’s filled with rows of green and yellow beans, beets, squash, and other vegetables during the growing season.

Surrounding the house itself are rock gardens filled with various flowers and shrubs, some purchased but most gifted by friends and relatives. Built over the years, they are part of our rural utopia. We take pride in what we’ve built and work hard to maintain it, but it has been a battle.

The Battle Begins

When we purchased our property, built the house, moved in from town, and started landscaping, we had no idea battling deer, woodchucks, and other wildlife, as well as insects, would be part of the rural routine.

Surprisingly, wildlife proves easier to deal with than various insects. One of the worst to cope with is the Japanese beetle, Popillia japonica.

Where They Came from and Where They Live

where they came from and where they live

As their name implies, these iridescent, coppery/green-colored little buggers are natives of Japan. The first adults appeared on American soil in 1916 at a nursery in New Jersey, believed to have arrived as grubs in a shipment of iris bulbs a few years earlier.

In Japan, the beetles cause little damage and are controlled by natural predators, but America was a new territory. With no natural defense measures, the beetles quickly moved west, north, and south.

By 2002, two years after we moved into our new home and started landscaping and enjoying the fruits of labors, Japanese beetles had become established in nearly every state east of the Mississippi. Today, they have firmly extended claim to areas in at least eight states in the Midwest and are pushing westward.

According to the USDA (U.S. Department of Agriculture), Japanese beetles are now one of the most widespread and damaging pests of turf, landscape, and ornamental plants in the United States as well as fruit, garden, and field crops, with damages and losses estimated at more than $450 million annually.

What They Eat and How They Damage

fighting back

As we quickly discovered, Japanese beetles don’t discriminate when it comes to eating. Over a few years, we toiled putting in everything from fruit trees and berry bushes to ornamental shrubs to perennial flower beds, not to mention a vegetable garden. Japanese beetles thanked us and took advantage of it all.

We didn’t know it at the time, but out of necessity and frustration, we learned from our local extension service that the pests are known to feast on some 300 different plant species. On their impressive menu are some of the most popular and desirable fruit trees, ornamental shrubs and flowers, and garden crops.

In the adult stage, Japanese beetles are especially drawn to beans, grapes, peppers, tomatoes, raspberries, blueberries, blackberries, strawberries, and apple, pear, and peaches trees. The adults will also eat the fruits and berries of these plants.

Much to my wife’s chagrin, roses are also a favorite target. In severe cases, the larva or grub will dine on these plants’ roots and many others. Chances are, if you grow it, or if it grows naturally on your property, Japanese beetles will take advantage of it.

Typically, adult insects begin eating along the uppermost part of a plant in full sun, consuming the greenery downward between the veins, eventually turning the leaves into a brownish, lace-like skeleton. If left unattended, the entire plant becomes entirely or partially skeletonized, if not defoliated.

In the grub stage, along with ornamentals, certain shrubs and many garden plants and the roots of grass and sod are especially susceptible. As a result, the plant’s ability to take in water and nutrients is reduced, especially in hot, dry weather, eventually turning entire patches brown.

Fighting Back

what they eat and how they damage

It took us a few years to realize some important things about Japanese beetles. One is that infestation is worse during some years than others. Mild winters with less-than-average snow cover and soils that freeze more deeply followed by dry, warm springs seem to reduce grub and adult numbers.

Adult female beetles instinctively lay their eggs in areas with adequate moisture to ensure offspring survival. And while older grubs are more tolerant of deeper freezes and dry spring conditions, even traveling deeper into the soil if necessary, in general, beetles in the grub stage seem to increase in normal soil conditions. They can withstand high levels of soil moisture during wet springs.

We’ve come to appreciate those rare mild winters and drier springs. But, we can’t always depend on Mother Nature to cooperate.

Another thing we’ve learned is both grubs, and adult beetles cause damage, and controlling one life stage may not prevent damage from the other. In fact, it seldom does. Both must be dealt with separately, and because Japanese beetles utilize such a wide variety of plants (often in large numbers), completely eradicating them is virtually impossible.

There are, however, ways to minimize the damage and fight back.

Preferring not to rely on chemicals unless absolutely necessary, our first attempts at battling adult beetles included attracting more birds to our property. Over time, several feeders, birdbaths, a couple of small fountains, and nesting boxes were placed, and we planted shrubs and ornamentals receptive to birds.

Honestly, it’s difficult to say whether the additions have made an impact. I believe they do during years of low infestation when natural foods are less abundant and during years of drought when birds flock to our water sources. But, they certainly haven’t hurt and have added a level of aesthetic appeal to our property.

We discovered one helpful thing by mistake while dealing with deer and other wildlife invading our vegetable garden. Our beans were doing fine during our second planting season and were about ready to flower, but one morning while visiting the garden, we discovered the tops had been munched overnight. The entire outer row looked like a freshly trimmed hedge.

Before it got out of hand, we started using floating row covers, leaving them each day until the crops matured, taking them off during the day, and replacing them at night when flowering. It solved the deer problem, and even though adult beetles were still evident, the plants were mature enough to produce.

Light-weight row cover material is relatively inexpensive and easy to use, is readily available at garden supply stores, and can be used on fruit trees, bramble bushes, and even flowers. Further, it will not damage tender, young plants and will hinder sun scalding.

Another measure we’ve taken is to continually plant shrubs, trees, and ornamental flowers of little or lesser interest to beetles in their adult stage, along with plants we desire. Japanese beetles do consume a long list of plants, but some trees, shrubs, and herbaceous plants are quite resistant, and the adults seem to avoid some of them.

lbor2Prime examples are ash, boxwood, forsythia, holly, lilac, juniper, and yew; begonia, California poppy, columbine, coreopsis, hosta, impatiens, pansy, and foxglove. Thinking the list may vary across the country, and some may not do well in certain regions, we checked with our local extension service for those that thrive in our area.

During years of low infestation and when damage seems to be localized, we found one of the best methods of battling adult beetles is handpicking them. It isn’t the most pleasant task and may not be for the squeamish, but adult Japanese beetles do not bite or cause any known irritations, and in most cases, it’s not even necessary to touch them.

Early in the morning, before they become totally active and are still somewhat sluggish, we simply use a bucket containing soapy water, position it under the host plant, branch or leaflet and shake it. In most cases, the beetles roll right off and into the bucket and drown to be disposed of later.

A popular line of attack is commercially available beetle traps, which we have tried and still use during low infestation years or when adults seem to be isolated to just a few plants. We also use them as a sort of a survey tool to determine the infestation level and whether other control measures are required.

Basically, these are bags equipped with two chemicals in a wax-like form, a sex pheromone and a floral lure designed to attract adults. When drawn to the trap, the beetles fall in the bag and can’t get out, and when full, the bag is disposed of or emptied.

In theory, the traps work well, but they can work too well. Japanese beetles will travel several miles to find host plants, especially when drawn by a strong attractant. The traps can actually draw beetles from other properties, thus bolstering your troubles.

Because of this, traps are best placed at least 30 feet from areas to be protected. Ideally, we like to hang traps downhill of our gardens as well. Doing so lures beetles away from our gardens, and those traveling from downhill will hopefully stop for a visit before reaching areas to be protected. We have very few neighbors where we live, but friends of ours who live in a more suburban area have pointedly gotten their neighbors involved in sort of a neighborhood beetle-control program.

In doing so, they’ve found that numerous strategically placed traps throughout the neighborhood work far better than one or two in their yard. Traps should also be emptied or replaced regularly, and like most things in life, timing is everything.

Depending upon the local weather conditions and severity of grub infestation, adult Japanese beetles are most active in June, July, and August. Traps are most effective when they’re out and about early in the season before serious mating and egg-laying begins.

One-Two Punch

one two punch

Whenever fighting Japanese beetles, a two-pronged attack is best. This means dealing with beetles in the grub and adult stages. This can be done culturally, chemically, and biologically. Some seem to work better than others, and which is best depends on the time of year and the infestation severity.

Keep in mind that Japanese beetle eggs and grubs need sufficient soil moisture to survive. During periods of peak adult-beetle activity, and the hot and dry periods of July, August, and early September, reducing or eliminating the watering of lawns, shrubs, and gardens can reduce the number of grubs.

During these periods, the downside of this is that these areas often require irrigation, so if watering is required, it should be applied sparingly and early in the day, allowing the water time to evaporate. There are numerous biologic-control products on the market, most containing milky spore, parasitic nematodes, or fungal pathogens.

The problem with these is they can be costly, depending on the area to be covered and the severity of the condition. They haven’t proven consistent or highly effective, again depending on the situation’s severity. They are also slow-working, and a second application may be required. These products are generally best applied in late August or early September when the grubs are smaller and closer to the soil surface.

Don’t Give Up!

Chemicals are the last option. Most soil insecticides have ingredients that do a reasonably good job at eliminating or at least controlling Japanese beetle grubs. They are available in liquid form, which can be applied with a sprayer, or granular form applied with a spreader.

Follow the manufacturer’s instructions or advice from your extension service, but most can be applied in the fall when grubs are small and before they burrow deep for the winter, as well as in the spring before they become active.

Finally, know that Japanese beetle eggs and grubs need moisture to survive. A good fall cleanup, mowing lawns short, and raking away fallen foliage in gardens around shrubs and trees will reduce moisture content. These areas will freeze deeper and allow your control methods to work more effectively.

Try out these tips, and hopefully, you’ll be able to save your shrubbery and gardens from obliteration by pesky Japanese beetles.

This article has been written by Andrew Houser for Prepper’s Will.

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