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Japanese Beetles

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If we knew what it was we were doing, 
it would not be called research, would it? -Albert Einstein

Japanese beetle: The beetles arrived in this country in 1912 on Japanese Iris bulbs and they were first noticed in 1916 in New Jersey. They have been slowly moving west ever since. Larvae is grayish-white, 1 inch long, has a dark brown head and two rows of spines. They lie curled up in the soil and burrow into deep soil to overwinter, pushing upward as the weather warms up in the spring. The adult is 1/2 inch in length, very fine hairs all over the body which is shiny bluish-green. The wing covers are a metallic copper, which shines various colors in the light and the head is bluish-green (they are hard to miss!) One generation every 1-2 years is produced. They eat and fly only during the day. They can cover an area up to 5 miles! The damage is seen as the familiar lacy looking skeletonized leaves on everything they attack. Several years of this destruction can seriously compromise a plants chances for survival.

The adults will eat most anything however their food of choice includes: flowers, fruit trees, roses and raspberries. They skeletonize foliage giving it the characteristic lacy look. The grubs chew on the roots of plants which is often seen in turf area damage. If you encounter a dead area of grass and can lift it right up you will probably find the Japanese beetle grubs to be the culprit. Raccoons and Canada Geese move into areas infested with Japanese Beetle grubs infestations and rip up the turf to feed on them.

Predators: Starlings...yes, those pesky starlings love to dine on Japanese beetles! Tachnid flies and tiphia wasps kill them. Native birds and chickens will feed on the larvae. You can help the birds along by turning the soil in autumn to expose the larva. Skunks and moles will go after them too. 

Repellent plants: Catnip, chives, garlic, tansy and rue.

Resistant plants: Bearing in mind they will eat most any greenery the following plants have shown to be less attractive to them: Box elder. Common lilac, Firs, Hemlocks, Hollies, Pines, Rhododendrons, Spruces, Scarlet oak, Tulip tree, White ash, White poplar and Yews.

Control Methods:

  • Trap crops for the beetles are African marigold, borage, evening primrose (oonthera), four o'clocks, knotweed, soybeans, white roses, white and pastel zinnias, wild grapes and blackberries.
  • Make bait traps of water, mashed fruit, sugar and yeast. Place on the perimeter of the garden at least 1 inch off the ground in plastic jugs with an entrance hole cut at the top. Choose sunny spots and strain the bodies out of traps every evening.
  • For easier handpicking : In the morning spread out a sheet under infested plants. Shake the plants and the beetles will fall onto the sheet. Dump them into a bucket of soapy water. Dew on their wings in the morning keeps them from flying away. The cooler air also makes them more lethargic.
  • Use pheromone traps keeping them at a distance from victim plants so you won't attract new beetles.
  • Use inter-plantings of four o'clocks (Mirabilis), larkspur, white geraniums, red (and dwarf) buckeyes whose flowers attract and poison the beetles. The leaves of the castor bean plant also poison them. These plants are poisonous to people to so be careful using them around children or pets!
  • Milky spore disease known as Bacillus popilliae can be used against the grub stage as a most effective long term control. This is best done on a wide scale treating entire infested areas in neighborhoods or grasslands. Complete control may take a few years. Once it does take effect the control can last up to 15 years!
  • Japanese Beetle Trap and Bait
    The following bait and trap method is to be used during the height of the Japanese Beetle season.

    1 cup water
    1/4 cup sugar
    1 mashed banana
    1 pkg yeast

    Dissolve sugar and yeast in the water. Mix the well maxhed banana into the sugar water. Put all ingredients in a gallon milk jug. Place the jug (with the top off) in an area where Japanese Beetles gather. The fermentation  and odor of the bait attracts the beetles which get in but not out.
  • Trap crops for the beetles are African marigold, borage, evening primrose (oonthera), four o'clocks, knotweed, soybeans, white roses, white and pastel zinnias, wild grapes and blackberries.
  • Nematodes: Another control for the grub stage is to apply beneficial nematodes to the infested area. These are applied at a ratio of 50,000 per square foot of targeted area.
  • Botanical Control: Pyrethrin, ryania or rotenone.
  • Bug Juice spray: If you can handle it this is supposed to work. Harvest about 1 cup of beetles, put them in an old blender and liquefy them. Thin this with enough water to make it pass through a sprayer. Spray it on any plants they victimize. NOTE: If you make this out of beetles infected with the milky spore disease you will actually infect more grubs with the disease. So...if you can handle it give it a try!


Update: 02/24/15


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