Killing Spanworm

If your clients' snowbush hedges (Breynia nivosa and compact B. disticha cultivars) seem to be fading away, look for the snowbush spanworm. To eradicate the pest, spray solutions containing B.t. (Bacillus thuringiensis) or a spinosad-containing insecticide product (ferti-lome's Borer, Bagworm and Leafminer & Tent Caterpillar Spray). Both of these insecticides are a narrow spectrum insecticide choice, meaning only the bad bugs will be affected. A labeled, horticultural, insecticidal soap spray may eliminate the smaller larvae.

The snowbush caterpillar is more abundant this year than in previous years and is stripping the foliage from attractive shrubs. The caterpillar became abundant in the summer of 2005 and settled in since then and can be found almost year-round. Usually snowbush hedges will re-sprout in a short time, but to make matters worse, some properties may have so many caterpillars that once the foliage is eaten, the spanworms start chewing on the twigs and bark. Caterpillars will defoliate the shrubs and start chewing the bark off of plants so severely that it resembles rabbit feeding.

The yellow and black larva (caterpillar) is the immature stage of a moth called the white-tipped black moth. Only the caterpillars cause the injury. At about only an inch long, the larva is full grown and ready to change into a pupa. Hedges typically have mixed populations of mature caterpillars (only 1-inch long) as well as newly hatched larvae, under one-eighth inch in length. When this caterpillar cannot find its favorite snowbush meal plant, it will feed on Otaheite or Malay gooseberry (Phyllanthus acidus), and supposedly white sapote (Casimiroa edulis), and snow-on-the-mountain (Euphorbia marginata).