How to Eliminate Spiny Witch Hazel Gall Aphids
It takes the spiny witch hazel gall aphid two years to complete its life cycle. These insects begin as eggs on witch hazel that hatch in the spring, crawl into the flower buds, cause the witch hazel to form a spiny gall into which the next generation fly before making their home in a nearby birch tree and hibernating until the following spring. Then they go back to the witch hazel where the female aphids produce offspring. If you have an infestation, you should begin eradication efforts in early spring when they are either beginning to hatch or just laying their eggs. Does this Spark an idea?
Instructions
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Buy lady bugs to kill the aphids if the infestation is minor. Lady bugs are desirable insects to have in the garden and are available at most large home improvement stores or from online retailers.
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Use pruning shears to cut off the leaves where eggs have been laid if the infestation is minor. Use a saw to remove entire limbs if necessary and practicable.
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Purchase a pesticide that lists the host plant (witch hazel) and the insect (spiny witch hazel gall aphids) on its label. Follow the directions on the pesticide's label before spraying it on the infected witch hazel when its buds are just beginning to break in early spring. This will help prevent the spiny galls from forming. You may need to reapply the pesticide every year.
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Apply a systemic insecticidal soap to the soil under the witch hazel if you don't want to spray it with pesticides. Follow the directions on the label carefully. Once again, do this in the spring so that the roots of the tree move the insecticidal soap into the sap where the aphids will suck it up. The soap will do little harm to any lady bugs.
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Drench the soil in the fall with imidacloprid, sometimes sold as Merit. Like the soap, it will make its way into the sap and will limit the harm done to lady bugs also living in the tree.
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