Diagnosis of Japanese Beetles
Symptoms
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Look for emerging adult beetles any time after mid-June. The are easily spotted on leaves and flower petals or buds as they eat. Beetles chew chunks from the middle of each leaf, sometimes removing all the leaf tissue between the veins completely. A serious infestation easily can skeletonize all of the leaves and flowers on a rose bush. Hybrid tea roses are like a magnet to Japanese beetles and just a few of the pests can do serious damage if ignored. As a general rule, if you see a little damage on a plant caused by a few transient Japanese beetles you can ignore it. If there are numerous beetles all over a plant, deal with the problem aggressively or there will be even more next year.
| Plants Commonly Attacked | ||
|---|---|---|
| Dahlias | Elm trees | Grapes |
| Green beans | Hollyhocks | Linden trees |
| Raspberries | Roses | Zinnias |
| Other Plants Attacked | ||
|---|---|---|
| Asparagus | Aster | Astilbe |
| Azalea | Rhododendron | Canna |
| Cosmos | Daylily | Delphinium |
| Ferns | Foxglove | Holly |
| Horsechestnut | Marigold | Peony |