Elderberry Under Seige
We have just found something (caterpillar- larva like) on the leaves of our elderberry bush, Sambucus nigra "eva. The culprit has appeared the last few years and almost defoliates the shrub. What might it be and how can we control it. Could it be an elderberry sawfly? That is the best we could find.
Wayne County Michigan
Although these larvae are similar to caterpillars in appearance, they are really wasp larvae. As such, they are not controlled with B.t.k.; instead, they require carbaryl (Sevin) or another chemical insecticide to achieve control. If you prefer a more organic solution, a combination of Insecticidal Soap and Botanical Pyrethrins should kill Sawfly Larvae on contact.
Insecticidal Soap (Potassium Salts of Fatty Acids) & Pyrethrin - The soap will penetrate the insect's shell and kill it by dehydration. Adding Pyrethrin creates the organic equivalent of a one-two knockdown punch. Pyrethrin is a nerve agent that will absorb into the insect and kill by paralysis.
Keep in mind, this soap is not like dish detergent, it's a base from a blend of plant sources and pyrethrin oils and come from the chrysanthemum flower.
When shopping for a pesticide, be sure to choose one that lists sawfly larvae on its list of pests controlled. As always, carefully read and follow all label directions; keep pets away, and wear protective clothing and gloves. It is recommended with any pesticide to test plants for sensitivity to the product. Spray a small section of the plant in an inconspicuous area and wait 24 hours before full coverage.