Question
We've had worms stripping the leaves on our birch tree stand.  Some worms about 1.5-2 in. long, green and off white long stripes with orangish feet and head.  What can we do to stop them from reappearing.  We torched all that we could see off the branches.

Answer
My guess would be a Luna moth or a close species.

The bright green full-grown caterpillars are 55 to 70 mm in length (Godfrey et al. 1987). There is a yellowish-white sub-spiracular line on abdominal segments one through seven and posterior yellow lines extending across the dorsum of segments one through seven to just above the level of the spiracles. A mid-segmental transverse band of setae-bearing scoli occurs on all thoracic segments and abdominal segments one through eight. The body is sparsely covered with short, white, spatulate setae. The head varies from green to brown. Just prior to pupation, caterpillars turn a reddish color.

Northernmost populations most often utilize white birch, Betula papyrifera Marsh, as a host. More southerly populations use a variety of host plants particularly members of the walnut family Juglandaceae (walnuts [Juglans] and hickories, [Carya]); sumacs (Rhus); sweetgum, Liquidambar styraciflua L.; and persimmon, Diospyros virginiana L. (Tuskes et al. 1996). Villard (1975) lists hickory as the preferred host, but recommends that rearing be done in sleeves or cages on living plants since most hickories wilt rapidly when cut. This obstacle can be overcome by diligently supplying fresh food. Sweetgum works well for captive rearing.

Luna caterpillars gain protection from predators by their cryptic green coloration. When threatened they often rear the front part of the body in a "sphinx" pose ?possibly to make them less caterpillar-like to a predator. If attacked, luna caterpillars as well as those of many other bombycoid moths make a clicking noise with the mandibles ?sometimes as a prelude to or accompanied by defensive regurgitation of distasteful fluids.

When caterpillars are full-grown, they may begin to wander. The cocoon is spun among the leaves of the deciduous host plants but is not anchored to a twig as is the case with many polyphemus moth cocoons. Therefore, they fall to the ground in autumn (Holland 1968) as the leaves fall and are not commonly seen. Development from hatching to pupation takes a month or longer depending on temperature.

Luna moth caterpillars are never sufficiently common to cause significant damage to their host trees.

Insecticides can be sprayed on treess in the yard setting but are not needed in a forest situation since there is very little real damage that the caterpilar does to the overall health of the trees.
Bt can be use as a spray for the smaller instars of the caterpillar but Orthene should be used for the larger instars. Bt has to be eaten by the caterpillar while Orthene is a contact insecticide and kills almost at once.