One given in the American Gardener’s almanac is that between the months of June and August, a flurry in concern about Japanese beetles descends with them across the country. With their metallic green shells, these rose-loving pests are yet to let up, even with pest control measures in place by countless gardeners, farmers, and horticulturists generally. Although they are one of the rarer pests, adult Japanese beetle damage can be truly devastating. Japenese beetle grubs have been known to defoliate a tree in a matter of days.

What Plants Do Japanese Beetles Attack?

As adults, Japanese beetles can feed on around 400 species of plants that grow within gardens in the United States. Trees and shrubs that attract more beetles include ornamental shrubs like roses and a sizeable variety of trees. They also present something of a double whammy in that they feast on different plants as both grubs and beetles.

What Plants Are Japanese Beetles Most Attracted to?

The softer the plant’s flesh, the greatest risk.  This, unfortunately, includes fruits and vegetables as the greatest casualties. The leaves preferred by the Japanese beetle include those with softer foliage, especially fruits and flowers which are more delicate to the touch and which they work on in the flesh between the veins.

The most notable victims are roses and hibiscuses and fruits like grapes and raspberries. Vegetables most at risk are soy and maize. Those which will usually survive the brunt of Japanese beetles include the likes of Magnolia (with its tough leaves and flowers) red oaks, pines, red maples, and of course Holly, as well as fruits with a fairly tough skin.

One Interesting Exception

Geraniums, while loved by the Japanese beetle contain a compound that paralyzes them for around half-an-hour and is quite often used as a trap plant by more eco-conscious gardeners who will then collect them one by one and bag them before they are able to wreak any more havoc.

Japanese Beetle Life Cycle

  • Eggs – Japanese beetle eggs are white and oval. They are laid two to four inches in the soil, where they can absorb moisture before they hatch.
  • Larvae – Eggs will develop into grubs and can spend the fall and winter months developing into an adult. Japanese Beetle larvae are white grubs and go through five instars before fully developing into an adult beetle. In areas where larvae are feeding, there is often an increased area of damage.
  • Pupae – Pupae are cream and brown and approximately 1/2 inch wide. Once grubs are fully developed they enter the pupation stage, becoming adults.
  • Adults – Adult beetles release pheromones which are chemicals that help them communicate with other adult Japanese Beetles.

Grub Stage

Japanese Beetles spend 8 months of the year in the grub stage feasting on lawns’ roots. The wetter the grass, the larger the infestation is liable to be.

Although the roots of other plants are not completely immune, it’s the roots of lawns that suffer most during this stage. You’ll know this is the case by a quite severe case of die-back in your lawn which is often so severe that it exposes the topsoil. The positive side of finding Japanese beetle grubs on your lawn at this point is that you can take the opportunity to stop them in their tracks before they develop tougher jaws and mandibles capable of working through your trees’ leaves.

One of the best solutions for curbing further growth is to grab a bag of fertilizer that says “Grub Control” on the label. Apply the grub control fertilizer over the resulting bare patches of grass.

Alternatively, buy a bag of fertilizer that supports nematode growth. It’s these microscopic little creatures’ whose job it is to eat grubs. This is definitely the most environmentally friendly solution as well.

As Beetles

With their small wings, they are not strong fliers, but Japanese Beetles tend to prefer feasting on foliage that grows in sunny areas of the garden. This includes the foliage of mature trees, although larger trees will be able to withstand an invasion of the insects without much long term damage.

The beetles will not touch pine trees and are less apt to attack yews, spruces, or forsythia.  At this stage, they tend to seek out softer-leaved maples, oaks (like the tender pin oak), and fruit trees, along with vegetables that range from green beans to soybeans.

One way to swing this to your advantage is to place a pheromone trap at the border of your smallholding or garden. Especially if you can find a suitable trap that doesn’t sabotage other beneficial bugs, this is a great and easy way to check a mass infestation.

For an in-depth List

For a more exhaustive list of the best and worst-faring plants in the midst of a Japanese beetle infestation, you can visit the website for the USDA. If you’re unsure, the tell-tale signs of an invasion of neighboring plants in your area are the best guide.

The Problem With Japanese Beetle Traps

When you first spot Japanese beetles in your yard, you might think that placing Japanese beetle traps would be the most logical next step. However, Japanese beetle traps can in fact make the pest problem worse if they are not used properly. Studies show that these types of pest traps can attract Japanese beetles from more than 5 miles away. If you live in a residential area, this can be a major problem.

Proper Way to Use Japanese Beetle Traps

If you follow the best practices for Japanese beetle traps, then they can be highly effective. To start, avoid placing the traps close to flowering bushes and plants that may attract Japanese beetles. Experts recommend placing the traps at least 30 feet away from such bushes and plants.

Because the trap will fill up rather quickly, it is best to remove beetles from the trap in order for it to remain effective. Failing to remove Japanese beetles as the trap fills up will result in an overflow of beetles that will cause them to find bushes and plants to destroy.

Other Notable Exceptions

Plants with which pungent garlic or onion aroma are usually immune to attack. This is also true of pines.

Farmers have also known for a long time now that some cultivars of fruits are hardier against attack than others, so it’s worth choosing your blackberry variety (for example) more carefully next time you pay a visit to your nursery, especially if Japanese beetles pose a threat in your area.

Here is a further list of vulnerable and less vulnerable plants Japanese beetles attack for the sake of illustration. It should be noted that these beetles will attack even some of the hardier plants on the list for lack of better options though. Click here for more information.

Plants Do Japanese Beetles Attack

While adult beetles feed on more than 300 types of plants in home gardens, the most common plants include:

  • Peaches, Apricots, and plums
  • Roses
  • Beans
  • Grapevines
  • Crab apples
  • Crape myrtle
  • Birch
  • Hibiscus
  • Japanese maple
  • American linden
  • Pin oak
  • Norway maple
  • Raspberries
  • Buckthorn shrubs

Plants Least Likely to be Attacked by Japanese Beetles

  • Boxwood
  • Ash
  • Clematis
  • Burning Bush
  • Fir
  • Dogwood
  • Forsythia
  • Holly
  • Hemlock
  • Magnolia
  • Lilac
  • Northern red oak
  • Redbud
  • Pine
  • Red maple
  • Yew
  • Spruce

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