June 13, 2003

Christmas Tree Scouting Report -
Number 12

Welcome to the Christmas Tree Scouting Report for the week ending June 13, 2003. To receive a FAX of this week's message, please call (814) 865-1636. To report pest activity at your location or request email report, please call 717 772-5229. For local Growing Degree Day information, please go to and click on Crop Weather along the left margin.

This week in Adams, Dauphin and Lebanon counties the eggs of bagworm were beginning to hatch. Mike Masiuk also reported larvae on conifers in western PA. The caterpillar of this moth is about 1/8 inch long when it first emerges. Very shortly after egg hatch inside the bags of the females, the caterpillars spin a silken thread and drop from the bag. This week, we could find young caterpillars hanging from silken threads beneath old female bags or feeding on host needles on lower branches. Soon after starting to feed, the caterpillar starts constructing a case out of bits of host material tied together with silk. It will carry this bag around until it matures. The larva continually adds to the bag and contracts into it, for protection, while it feeds and grows. Once these bags reach about 2 inches in length the larvae will attach their bag securely to the plant. Pupation takes place in the bag in late summer. Males emerge from their bags and fly to wingless females, which remain inside their bags. After mating, females deposit eggs inside their bag before dying. These eggs will overwinter till next spring. Chemicals are more effective when applied shortly after egg hatch while larvae are still tiny. Check the recommendation sheet for chemicals listed for this year. A follow-up application about 10 days later may be necessary.

Last week cryptomeria scale was beginning to produce eggs of the first generation at some of our monitoring sites. This week at all sites monitored in Berks, Dauphin, Lebanon, Lancaster and York, lemon yellow eggs were found under the female scale covering. Like all armored scale the best time to apply an insecticide is when crawlers begin to emerge. We will continue to monitor for crawler emergence during the next couple weeks.

Some growers may have noticed a black-headed larva on their pines. It is about 1 inch long, with yellow and white spots on a black background. This is the introduced pine sawfly. It was found this week in Lebanon County on white pine. These insects' feeds on the needles of most pine species but are usually not abundant enough to cause injury. Unlike other important sawfly pests of Christmas trees, such as the European and the redheaded pine sawflies that feed in colonies and defoliate whole branches, the introduced sawfly feeds in groups when young then disperses and feeds singly causing less damage to the tree. Control is usually not necessary because natural enemies and low winter temperatures keep this pest at tolerable levels.

Botrytis blight, also known as "gray mold", is beginning to appear at most Douglas fir sites visited this week. Damage is reminiscent of the freeze damage in 2002 or of Sphaeropsis tip blight on Scotch pine. Botrytis is a fungus that can attack all conifer species grown for Christmas trees and is fairly common. Extended cool, wet weather during shoot elongation, when immature tissue is most susceptible, is the perfect opportunity for Botrytis to develop. As weather warms and less moisture is available, disease activity ceases. Shearing should remove most damaged shoots.

Douglas-fir needle midge adults have emerged from their overwintering sites underneath infected host trees. These small, delicate flies mate following emergence and females have already deposited elongate pale eggs at the bases of newly emerging needles. At a site in Lehigh County, the eggs are already hatching and larvae are boring into young needles. This activity causes the needles to swell and turn yellow at the site of attack. Infested needles are also frequently bent at the site of the gall. We are aware of several infested sites in Bucks and Lehigh counties and would like to survey as many sites as possible this summer. If you are growing Douglas fir in either of these counties and would be willing to let us visit your site, please contact either Rayanne or Sandy at 717 772-5229 or 717 772-0521, respectively. You may also email Rayanne at