How can I treat soil for wood borers? They killed three 35-year-old Mahonia Beali, and I need to replant the bed.
Borers were diagnosed by Bartlett Tree Service from orange frass around the stems at the soil level.
Answer
Dear gardener: I suspect the borer did not come from the soil, but is the result of eggs being laid on your Mahonia by a flying moth of some sort. These eggs hatch into larvae which crawl through the bark or a bark fissure and interfere with water transportation up the plant stem. To control this organism requires spraying the stem with an insecticide when the larvae are hatching. Timing is critical. Companies that spray for borers know the exact timing as it varies with the temperature of the season. Borers tend to attack (moths lay eggs) plants that are stressed by a harsh winter, drought or difficult growing conditions. Try to select replacement plants that are best suited to your soil and growing conditions.