Question
our trees, fruit, rose bushes but apple trees are fine.  They are getting eaten by 1" x 1/8th inch green worm/caterpillar.  What can we do?  Is BT a solution?  If so, where can you buy it?

Answer
Bacillus thuringiensis (Bt) is a live microorganism that kills certain insects and is used to kill unwanted insects in forests, agriculture, and urban areas.

Bt is a species of bacteria that has insecticidal properties affecting a selective range of insect orders. There are at least 34 subspecies of Bt1 (also called serotypes or varieties) and probably over 800 strain isolates. Bt was first isolated in 1901 in Japan from diseased silk-worm larvae. It was later isolated from Mediterranean flour moths and named Bacillus thuringiensis in 1911. It was not until 1958 that Bt was used commercially in the United States. By 1989, Bt products had captured 90-95 per cent of the biopesticide market.

Bacillus thuringiensis products available in the United States are comprised of one of five varieties of Bt: Bt var. kurstaki and var. morrisoni, which cause disease in moth and butterfly caterpillars; Bt var. israelensis which causes disease in mosquito and blackfly larvae; Bt var. aizawai which causes disease in wax moth caterpillars); and Bt var. tenebrionis, also called var. san diego, which causes disease in beetle larvae. Other strains of Bt have been discovered that exhibit pesticidal activity against nematodes, mites, flatworms, and protozoa.

Bt products are used to control moth pests in fruits, vegetables, and beehives; blackfly and mosquito pests in ponds and lakes; and several beetle pests in vegetables and shade trees.   Common brand names include Dipel, Foray, Thuricide (all Bt kurstaki), Vectobac, Mosquito Attack (all Bt israelensis), and M-Trak (Bt tenebrionis).

You will be able to buy it at a nursery or garden type store under the above brand names. It will kill any caterpillar type insect by the insect eating the Bt. The caterpillar will have to eat the Bt so it will take a day or two for the insect to die.

Contact insecticides like Orthene will kill the caterpillars as soon as they are sprayed.