ask-ruth-pictureDear Ruth,

This is my second year at gardening and I am wondering what to do about Japanese Beetles. Last fall I lay down the milky spore and that has seemed to help some. I spray with a soap/oil solution, sanafad?…pick them off. They are devouring everything. Anything else to try? Not gonna use poisons.

Thank you for your time,

Rhonda

Dear Rhonda,

Japanese Beetles can be discouraging, and it is a bit nerve-wracking when they arrive in droves and decimate your plants seemingly overnight. It beetlesounds like you are taking the right steps already, but (Yikes!) you are still dealing with lots of beetles.

Japanese beetles were first discovered in the United States in 1916, and are present in most states east of the Mississippi River and in a few of the western states. They are very pretty bugs, having 3/8” long metallic-green bodies with iridescent copper-colored wing-covers. Japanese beetles feed on the foliage, flowers, and fruit of a wide variety of plants, but have a preference for about 50 different plants. Some of their favorite foods are roses, Japanese maples, apples, peaches, plums, cherries, grapes, raspberries, crape myrtles, linden, and birches. Commercially they can compromise corn and soybean crops. As they feed, they will skeletonize or completely destroy plant leaves. They love to eat rosebuds. Apparently they send out an APB when they find likable food, and feeding females release powerful sex pheromones that will quickly attract males in droves.

Japanese beetles usually emerge in June-July and hang around for about a month. They
mate and lay their eggs mostly in grass and lawns. The eggs hatch in late summer/fall and the grubs begin feeding on plant roots until the weather cools down. They overwinter in the ground and resume feeding in spring once the weather warms back up. Japanese beetle grubs feed on a number of different plant roots ~ but they love grasslands and lawns. Kentucky bluegrass and tall fescue (both prevalent in the mountains) are among their favorites.

Lets go over some options for controlling Japanese beetles:

HANDPICK: Generally, I don’t hesitate to squish bugs and smash their eggs with my fingers, but I have to admit ~ squashing Japanese beetles bare-handed is a bit intimidating. They seem to drop to the ground and disappear when you try to hand pick them, so I think it helps to have soapy water to drop them in. Rather than dropping them into a jar, I have switched to brushing them off the leaves into a bowl of soapy water (the wider opening captures more of them). Hand picking is best achieved in the morning when the beetles are more sluggish. Linda Blue, Buncombe County Extension agent, thinks handpicking is one of the most effective ways to deal with Japanese beetles. Why? If you spray them with an insecticide today, you will kill some of them, but more beetles will arrive the next day.

MILKY SPORE: The idea with Milky Spore is that if you get rid of the grubs, you will reduce beetle populations. Milky Spore contains the Milky Spore disease bacterium Paenibacillus (formerly Bacillus) popilliae. These bacteria will kill the grub stage of the Japanese beetle by eating it from the inside out. Milky Spore is not harmful to humans, pets, beneficial insects, wildlife or aquatic life, and comes in two formulations.

  1. The powder formulation will only have to be applied once, and can be applied anytime the ground is not frozen (10 ounces treats 2500 ft.). It is applied every 4 feet in teaspoonfuls. Each teaspoonful contains 100 million spores.
  2. The granular formula (in 20 lb. bags that cover 7000 sq. ft.) should be applied with a drop spreader 3 times a year (spring, summer, and fall) for 2 years (or 6 applications over 2 years).

The Milky Spore should be watered in after it is applied. The advantage of the granular mix is that it is applied over the entire surface of the yard, so spores are present everywhere and the likelihood of a grub eating a spore is increased. When each infected grub dies it will release 3 billion new spores into the soil. So Rhonda…spore numbers will increase every time a grub dies and will increase with each passing year; lasting up to 15 to 20 years. Spore numbers increase more slowly in the Northeast where the weather is colder. Rhonda, I have one question for you about your Milky Spore application ~ If you used the granular formulation, have you applied the follow-up applications?

JAPANESE BEETLE TRAPS: Japanese beetle traps definitely work. The bait for the trap is either a sex pheromone, or something that smells like yummy beetle food. At the prospect of good food or a chance to mate, the beetles congregate quickly. The problem with the traps is that they often attract more beetles into your yard/garden than would have naturally been there in the first place. If you use beetle traps, set them as far from your garden as possible and empty them religiously (daily). Consider putting them out only a couple of days a week.

INSECTICIDAL SOAP: The soap must actually hit the beetle directly. Spray in early morning when beetles are sluggish.

SURROUND®: Surround® is a white kaolin clay that is mixed with water and sprayed on plants in liquid form. It is used on many fruits, tomatoes, cucumbers, squash, and other vegetables. The white color of Surround® seems to confuse pests and the clay barrier is an irritant. A white residue (non-toxic) may remain on the fruit at harvest time and can be washed off with water.

FLOATING ROW COVER: Row covers are a very lightweight spun polypropylene fabric that rain and light can pass through. You can use floating row cover to wrap particularly delectable plants, or even cover a small garden completely. The floating row cover acts as a physical barrier so that Japanese beetles are unable to access the plant. You will need to leave some room for plants to grow.

BENEFICIAL INSECTS: Two parasitic wasp species, Tiphia vernalis and T. popilliavora, are natural enemies of the Japanese beetle grub. They were imported from Japan, Korea, and Northern China as early as 1021 as biologocial controls that will attack the grubs. A tachnid fly, Istocheta aldrichi, will parasitize adult beetles. The presence of aphids, and Umbelliferous plants like fennel, dill, and Queen Anne’s Lace, will help retain these beneficials in your garden.

NEEM: An application of Neem Oil as soon as beetles are spotted can help diminish feeding. Apply every 7 days while beetles are feeding. To prevent leaf burn and to avoid hurting honeybees, spray Neem Oil late in the evening.

PYRETHRIN: Pyrethrin is extracted from the chrysanthemum plant and is noted for its ability to provide quick “knockdown”. However, knockdown doesn’t necessarily mean death. To be effective you must spray the pyrethrin directly on the Japanese beetle, so be thorough when you spray. Along with the top parts of the plant that you can see; be sure to spray the undersides of the plant as well.

MYCOTROL: I am not aware of this product being sold in smaller containers for gardener use. Mycotrol contains a naturally occurring fungus, Beauveria bassiana strain GHA. According to the EPA “Many strains of Beauveria bassiana are found worldwide in the soil. They control insects by growing on them, secreting enzymes that weaken the insect’s outer coat, and then getting inside the insect and continuing to grow, eventually killing the infected pest…Tests show that the fungus is not toxic to mammals, birds or plants. There is a potential for the pesticide products to harm bees, so the products must not be applied near beehives or where bees are actively hunting for food.

Rhonda, I am not sure what Sanafad is, but I wonder if you meant SPINOSAD. Monterey Garden Insect Spray and Captain Jack’s Dead-Bug Brew are two retail products with Spinosad as the active ingredient. The active ingredient is a rare soil dwelling bacterium called Saccharopolyspora spinosa. It was discovered at an abandoned rum distillery by a scientist on vacation in the Caribbean in 1982. Neither of these products specifically names Japanese beetles on the label, but they both say that they target leaf-eating beetles. Spinosad should also be sprayed late in the evening to avoid honeybees.

Researchers are studying GERANIUM PETALS as a possible Japanese beetle control. According to the Agricultural Research Service ~ when Japanese beetles eat the petals of a geranium flower, within 30 minutes they roll over on their backs, their legs and antennae begin to twitch, and they are paralyzed for a few hours. Even though they are typically recovered within 24 hours, they often fall victim to predators, since they are unable to defend themselves while they are paralyzed.

OTHER IDEAS I GLEANED FROM MY RESEARCH:

  • Vacuum the beetles off your plants with a dustbuster.
  • Deter Japanese beetles by grinding up your captured beetles in a blender with water, and spraying them back on the plants.
  • Spray plants with garlic sprays.
  • Kill the grubs by walking over your lawn numerous times wearing aerator sandals (they’re spiky), or running an aerator over your yard a few times.

So Rhonda, there doesn’t seem to be a magic bullet for Japanese beetles, and it looks like you are already on the right track. Keep up the good work and try experimenting with any of these ideas that appeal to you. I’d like to end our discussion of Japanese beetles with this optimistic note ~ Japanese beetles like to eat poison ivy and multiflora rose!

Thanks for writing,
Ruth

Ask Ruth © 2013 Ruth Gonzalez & Organic Growers School

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Ruth Gonzalez

Ruth Gonzalez

Ruth Gonzalez is a former market farmer, current gardener, and local food advocate. She has written numerous local food and gardening articles, blogs about local food, and writes the “Ask Ruth” Gardening Column for Organic Growers School. In her job at Reems Creek Nursery, Ruth offers advice on all sorts of gardening questions, and benefits daily from the shared wisdom of local gardeners. She has a special affection for clouds and finds delight in the natural world at every turn. Read more from Ruth at her blog: http://tailgatemarketfanclub.wordpress.com/