Growers of true firs are advised to continue watching for the minute yellow crawler stage of this troublesome armored scale. Bagworm larvae in Lancaster and York counties have constructed their protective bags using bits of host material held together with strong strands of spun silk. The inch long bags are easy to overlook and the feeding damage is still insignificant. However, this is the best time to control these moth larvae by using a biological insecticide, Bacillus thuringiensis , or Bt. Spruce, Douglas fir, and pine are all susceptible hosts and can be defoliated by these voracious caterpillars.
Spider mites continue to build populations on spruce and fir at many locations.
Judging from the calls received recently, growers are really starting to notice the mites because their damage has become apparent. The best time of year to control the mites is when the population is building, usually in early spring or fall. At these times, controls can be applied to prevent damage and some of the newer materials that only require a single application can be effective. However, at this time, the populations are reaching their spring peaks and a material that is capable of quick knockdown is the choice. Many traditional miticides will serve the purpose but only if a total program of two applications 7-10 days apart are included in the plan.