Gardening with Gary

Gardening Advice from an Expert

Japanese Beetles

Q. In past years, I have had major problems with Japanese Beetles. They are especially destructive to string bean plants. Can you suggest some organic remedy to rid of these darn pests?

A. You have touched upon a longtime nemesis of our garden plants. I remember first confronting them in Ohio around 1963. They are as ugly as they are nasty and voracious.

Organic compounds have not been very successful against these large critters. You could try the Safer Insecticidal Soap products which have been out for a while and have a greater range of success than prior mixes.

I have not attempted to control them with Safer's, but you could give it a try. I had read of an insect that was being experimented with to see if the beetle larvae would be eaten. Once they have developed that hard outer shell, they are hard to penetrate and kill. The larvae may be the better stage of the insect to attack.

Check with your local ag department as to whether there is a beneficial insect available, and if they are using any nontoxic organic compounds in the eradication. If you find out something newsworthy, please tell me!

Q. I have some Japanese beetles in my garden. What should I do?

A. Please treat them as soon as you can. They are terribly destructive and eat rapidly. Follow the label instructions always and take care to avoid breathing in the spray, apply on a still morning, and wash hands and arms carefully with warm soapy water after use.

Here is pertinent info listed in this order:
Insecticide,
Amount to Mix with 1 Gallon Water,
Amount to Mix with 10 Gallons Water,

Comments.

Cythion 57% EC (Malathion)
1 teaspoon
1 1/2 fluid ounce
Do not use on Boston fern, maidenhair fern, Crassula, violets, Saintpaulia, petunias, gloxinia, some red carnations or maple or hickory under stress. Highly toxic to bees

Dymet (20/10) EC (Methoxyclor and Diazinon)
6 teaspoon
1/2 pint
none

Marlate 50% WP (Methoxychlor)
3 tablespoons
5 fluid ounces
none

Marlate 25% WP (Methoxychlor)
6 tablespoons
9 fluid ounces
none

Orthene 75 S (Acephate)
4 teaspoons
2 fluid ounces
Repeat applications of two week intervals as necessary

Sevin 50% WP (Carbaryl)
1 1/2 tablespoons
3 fluid ounces
Mites and aphids sometimes become a problem after Carbaryl sprays. Carbaryl is highly toxic to bees. Do not use on Boston ivy.

Adult Japanese beetles are 3/8-inch long metallic green beetles with copper-brown wing covers. Five small white tufts project from under the wing covers on each side, and a sixth pair at the tip of the abdomen, distinguish them from similar beetles. Adults emerge from the ground and begin feeding on plants in June. Individual beetles live about 30 to 45 days. Activity is concentrated over a four to six week period, beginning in July, after which the beetles gradually die. Japanese beetles can feed on about 300 species of plants ranging from roses to poison ivy. Odor seems to be a very important factor in the selection of a suitable food plant. They usually feed in groups, starting at the top of a plant and working downward, and prefer plants exposed to direct sunlight. A single beetle does not eat much; it is group feeding by many beetles that causes the severe damage. Adults feed on the upper surface of foliage, chewing out tissue between the veins. This gives the leaf a characteristic skeletonized appearance. They tend to do little feeding on thick, tough leaves. The spread of the Japanese beetle infestation is primarily the result of flight by the adults. They can fly as far as 5 miles but 1 to 2 miles is more likely. Usually, they make only short flights as they move about to feed. Local infestations spread as beetles move to favored food and suitable sites for egg laying.

Assistance from University of Kentucky, Agriculture/Entomology