May 10, 2006
Christmas Tree Scouting Report Number 9 - May 10, 2006
Weekly newsletter compiled by Sandy Gardosik, PA Department of Agriculture.
Larvae of the European pine sawfly were found feeding on Scotch pine in Dauphin County. A sawfly is really not a fly, but is actually a wasp. Part of the common name "sawfly" comes from the stout body that gives them a fly-like appearance, and the saw-like ovipositor the female uses to lay her eggs. The female cuts open the needle with her ovipositor and inserts the eggs into the open wound. Scotch and white pine are the most common Christmas tree hosts of the European pine sawfly. Eggs are laid in clusters, and when the larvae hatch they feed in colonies on the outer edges of old needles, producing tufts of dead needles. The larva is green with white and black stripes, and a shiny black head capsule. Older larvae eat entire needles, leaving only the needle sheath to remain. Since this sawfly emerges in early spring and feeds only on old foliage, trees are never completely stripped of needles. However, if populations are high, small trees can be stripped of old foliage and growth rate slowed. Look for tufts of strawlike needles, and larvae present on the old growth. Control larvae by spot-spraying with a registered insecticide, or simply remove them by hand.
Crawlers of elongate hemlock scale (EHS) are beginning to hatch on Fraser and Grand fir in Adams County. This scale was first detected in Pennsylvania in 1958 and is now found in most of Pennsylvania's eastern counties and also in Allegheny County. Control of this armored scale is difficult because of the protective armor that encloses the adult female and her eggs, and also because of this scale's unsynchronized life cycle. With this scale, crawlers are present throughout the growing season and do not emerge in short, well-defined "crawler emergence periods" that facilitate insecticidal control. The continued spread of this scale, the difficulty of controlling it, and the serious damage that it causes, made it obvious that research was needed. Dr. Paul Heller from Penn State University completed a three-year spray trial evaluation study in 2005, and his results showed that 4 applications of dimethoate 267 applied at 3-week intervals, begun when crawlers are first observed, produced an average mortality of 98%. Begin scouting your own fields for EHS, look for chlorotic spots on top of needles on the lower branches in toward the trunk. If chlorotic spots are found, check for scale on the bottom of needles. The adult female covering is a glassy amber color where as the adult male covering is white with long white waxy fibers. With a hand lens look for tiny, flat yellow crawlers either moving around on the bottom surface of the needles or sitting still, which would mean they began to insert their mouth part, and are beginning to feed, and will remain in this spot as they develop and produce their armor covering.
Adults of Douglas fir needle midge were found in emergence traps in Schuylkill County, where they could also be seen flying about host trees. In Bucks County adults are still being found in traps, eggs are still present among expanding new needles, and larvae can be found in needles that show early symptoms of kinking. Spray trials conducted in Bucks County in 2005 and 2006 will be evaluated this fall, and results will be shared at upcoming regional meetings.
Eggs of pine needle scale are beginning to hatch on Scotch and white pine in Adams County, and a few crawlers have been found on the needles. Look for tiny, paprika-colored crawlers on the needles. Control pine needle scale crawlers with two applications of a registered insecticide, 7- to 10 days apart.
If you have any pest information to report please email Sandy Gardosik at firstname.lastname@example.org or call (717) 772-0521 and give pest, host plant and county where observation was made and I will include this information in the next report.