Every year in our gardens and landscapes we have unwanted visitors that show up and leave a big mess.
They eat just about everything in sight and leave our plants in bad shape. These unwanted guests stay around for three to four weeks.
I received my first call this past week on these pests -- Japanese beetles.
Japanese beetles were introduced into the United States in 1916 in New Jersey. Since then, they have spread to the north, west and south. In Georgia, they are north of the fall line, but some have been found below the fall line.
They like heavy soils, such as Georgia clay.
Japanese beetles are very striking insects. They are a bright metallic green with coppery brown forewings that reach almost to the tip of the abdomen. There is a row of five white spots along the side of the abdomen and a pair of white spots on the top of the last abdominal segment. These spots help distinguish this beetle from similar beetles such as the Green June beetle.
Japanese beetles have a preference for the types of plants they like to eat. Two plants they favor are roses and crape myrtles. Other plants they like to eat are hibiscus, apples, pears, plums and vegetables, especially beans.
The damage they cause is easy to recognize. They eat the tissue between the veins of leaves, leaving just a skeleton of veins behind.
Also, they eat flowers. If you have blooming plants in the landscape, this is one of the first places you need to look for them.
Besides the adult beetle being a major pest, the larval stage is a plant and turfgrass pest as well. The larval stage, which is a white grub, eats the roots of plants.
To control Japanese beetles, an understanding of their life cycle is important. There is one generation per year. The adults emerge in late May or June and can be active until July. The adults will live four to six weeks, with the females laying eggs during most of their lives. The eggs hatch in two to three weeks. The grubs feed on the roots of plants and will become mature by early fall. The grubs over-winter in the soil, and in the spring they pupate and become adults.
To control Japanese beetles, the adults and the white grub stage need to be attacked.
There are a number of ways that these stages can be controlled. First, hand pick them when they are first seen. I use a small bucket that has soapy water in it. I then knock the beetles into the water. Another organic control option is to use Bacillus thuringiensis var. kurstaki or Bt, which is a fungus poisonous to the beetles.
If you want to use an insecticide, you can use Sevin. If you do, remember to use it late in the afternoon to reduce the chance of exposing bees to the insecticide. Imidacloprid is another good control option.
To control the grubs, there are two times when the treatments work best. The first and best is late August through September. The other time is in March.
The grubs are closest to the soil surface at these times. There is an organic control option available; this is a fungus called milky spore that can be applied. The fungus in milky spore is Bacillus popilliae . This product can be found in stores or online.
When milky spore is used, it takes two years for the organism to build up in the soil before results are seen. There are insecticides that can be used to control Japanese beetle grubs and other grubs.
Some of the products are imidacloprid, trichlorfon and halofenozide. These can be found in most garden centers. Make sure to read and follow the labels on all pesticides.
There is one control option that is not recommended in most situations. Most entomologists do not recommend the use of Japanese beetle traps. These traps have sex pheromones in them. They will trap the beetles, but will draw them into an area. However, if the traps can be placed a great distance from an area, they will shoo some of the beetles away.
Charles Phillips is a retired Columbia County Extension Service agent who operates Hort Consulting. He can be reached at firstname.lastname@example.org.
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