Organic Pesticides, Japanese Beetles & Grapevines

Identification

• Japanese beetles are 1/2 inch long and have a metallic green head and body with copper-colored wing coverings. The larvae are small, white and C-shaped. The larvae overwinter in the soil and emerge in the summer after pupating into adult beetles. The adults spend the summer feeding and mating and lay one generation of eggs before dying. Japanese beetles produce pheromones to attract a mate. The beetles tend to congregate in large groups.

Damage

• Japanese beetles leave large holes in grape leaves and may skeletonize the leaves, leaving only the veins and stems. They prefer tender, smooth leaves in full sun. They generally do not harm the fruit, but a lack of foliage may reduce vigor and fruit production.

Organic Pesticides

• Several organic pesticides are labeled for use on Japanese beetles. Spinosad is made from a naturally occurring pesticide and slowly paralyzes the beetles after they eat it. Spray neem oil directly on the beetles to slow feeding and reproduction. Neem oil may not completely control Japanese beetles, but it may reduce numbers adequately to prevent harm to the grapevines. Spray lawns infested with Japanese beetle grubs with milky spore disease. Larvae die after feeding on this bacteria, although effectiveness varies, depending on the product.

Considerations

• In addition to organic pesticides, handpicking Japanese beetles is an effective strategy for small populations. Knock the beetles into a bucket of soapy water in the morning when they are less active. The soapy water kills the beetles and destroys any pheromones, as well. Japanese beetle traps are not recommended. These products emit pheromones that attract the beetles, which then in turn attract more beetles. One trap can lure up to 10,000 beetles in a single day.