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Gardeners need reminders about common pests

Posted: May 27, 2012 - 12:18am

This past week, I saw one of the more dreaded insects that can attack our plants: the Japanese beetle. Also, I have been getting numerous questions about the squash vine borer and the squash bug.

Japanese beetles 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 eat the tissue between the veins of leaves, which will have just a skeleton left. They also like to eat flowers. Blooming plants are one of the first places to look for them. Besides the adult beetle being a major pest, the larval stage is a plant pest as well. The larval stage, a white grub, eats the roots of plants. They are a major pest of turfgrass

There are a number of ways to control the adults. The first is to hand-pick them when they are first seen. Another option is to use Bacillus thuringiensis var. kurstaki, or Bt, a fungus that kills the beetles after they eat it. Bt can be found in products such as Dipel.

One of the best insecticides for Japanese beetles is Sevin. Sevin is very harmful to bees, so it needs to be used late in the day after bees have gone home for the night. Another good insecticide is Imidacloprid. This systemic insecticide is put around the root system and moves throughout the plant. Imidacloprid will also control the grub stage of the Japanese beetle. The best time to apply this insecticide to control the grub stage is late August to early September.

An organic control option is a product called milky spore, which contains the fungus Bacillus popilliae. The fungus comes in contact with the grub, and the grub dies from a disease. It takes two years for the organism to build up in the soil before the best results are achieved.

The insect that gives most squash growers the most problem is the squash vine borer. Damage is caused by larvae tunneling into the stems of the squash.

Various measures can be taken to control this pest. The first is tilling the soil in late winter to expose overwintering insects. Another practice is to break the life cycle by destroying the vines that have been killed. Also, slitting the infested vine lengthwise and removing borers reduces their numbers.

Organic growers plant radishes around their squash to repel the adults. The use of insecticides will control squash vine borers, but they need to be used late in the day to prevent harm to bees. Insecticides such as bifenthrin, sevin, esfenvalerate and permethrin are effective on these insects, but each has a waiting period before the fruit can be harvested. Also, neem oil applied weekly can help control these insects.

The squash bug (Anasa tristis) is one of the more common and troublesome pests in the home vegetable garden. Squash plants frequently are killed by this sap-feeding pest. Leaves of plants attacked by the bugs may wilt rapidly and become brittle. The adult squash bug is rather large, brownish black, and flat-backed.

The secretive nature of squash bugs can be used to your advantage in controlling these pests. Place a small, square piece of old shingle or heavy cardboard under each squash plant. As bugs congregate under it for protection, simply lift the trap and smash them. Other control methods include early planting and removing eggs and nymphs by hand. Insecticides can be used, and the best is bifenthrin or esfenvalerate. Rotenone, an organic control, can be used when the insects are in the nymph stage.

Charles Phillips is a retired Columbia County Extension Service agent and operates Hort Consulting. Reach him at cphillipshort@comcast.net or at (706) 836-2152.

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