Gypsy moth is often in the news and with it comes the promise of aerial spraying of Btk by the department of agriculture. While the idea of the government spraying pesticides over an entire neighborhood may be frightening, a gypsy moth out-break would be devastating to the trees of the Emerald City or any city. Gypsy moths defoliate over 500 species of trees, both deciduous and evergreens.
Bacillus thuringiensis var. kurstakiis a bacterium that affects only caterpillars. It is considered an acceptable pesticide by organic gardeners, provided it used only when really needed. The major caterpillar pests in our area include:
- the larvae stage of the gypsy moth;
- cutworms that feed in winter and spring on primroses, chives and other perennials;
- tent caterpillar often seen later in the spring on apple trees;
- keep in mind that sawfly larvae which can strip a flowering red currant bare in a few weeks are not caterpillars, and Btk will not control them.
Btk will kill caterpillars of butterflies, which is why it must be used with caution only when pest populations are high or the potential damage is intolerable. Btk is typically sold as \”caterpillar killer\” where other pesticides are sold.