May 9, 2007

Christmas Tree Scouting Report #7 - May 9, 2007

Weekly newsletter compiled by Sandy Gardosik, PA Department of Agriculture.

Growers in Bucks, Dauphin, Juniata, Lebanon, Schuylkill and York counties are planning to begin their spray programs for Rhabdocline needle cast on Douglas fir this week. Three to four sprays are recommended for best control. The first application is applied when the field is at 10% bud break; apply the 2nd spray one week later; the 3rd spray two weeks after the 2nd.  During long cool springs, when new shoots harden slowly, a 4th spray may be needed 2-3 weeks after the 3rd spray. If you are also controlling Swiss needle cast in the same field a 4th spray is recommended since Swiss sporulates later than Rhabdocline.

Growers who are planning on spraying for spruce needle rust on Colorado blue spruce should follow the same spray program as for Rhabdocline needle cast.  Some growers claim they have experienced phytotoxicity with chlorithalonil on spruce. Contact your chemical sales representative for the appropriate rate.  At this time of the year spruce needle rust shows up as an orange band across the needle and will also be visible when the needle is examined from beneath.

White pine weevils and their feeding damage were found on the leaders of white pine in Dauphin and Juniata counties. When terminals were examined, eggs were found, but no egg hatch had occurred yet.  Weevil damage and eggs were found on Serbian spruce in York County.  White pine weevils were just beginning to show up in pyramidal traps in Warren County this week, and so the grower applied his first spray. Growers will scout for damage and continue to monitor traps to determine if a second spray will be necessary. 

Damage from eriophyid mites is starting to become evident on Norway spruce in York County. This tiny, wedge-shaped mite removes the green color from the needles, and when their populations get heavy, the needles turn bronze. The eggs and mites are smaller than those of spruce spider mite and can be difficult to see with a hand lens. It is usually the color change that alerts growers to a problem.

Balsam twig aphids were found feeding on the new growth of Concolor and Fraser fir in Juniata and Dauphin counties. At, or just before bud break, the stem mothers produce live young. The stem mothers and immature aphids are pale green and can be found feeding on the new growth. If you decide to control these aphids, insecticide must be applied before the trees start to break bud for best control. The aphids are sheltered from pesticide applications by the immature needles, and-- if cones are present -- aphids also can hide under the cone bracts.

Cooley spruce gall adelgids were found on the new growth of Douglas fir in Bucks, Dauphin, Juniata and Lebanon counties. The best time to control Cooley adelgids and prevent damage to the new grow is in the fall, between September and October or early spring before adelgids cover themselves with protective white, waxy fibers.

Galls from the eastern spruce gall adelgids adult females are starting to become evident on Norway spruce. The female adelgids lays about 100-200 eggs under a white, waxy, cotton-like covering. As the spruce buds expand feeding from the adult female cause the lower needles in the bud to swell and lightly discolor. Once eggs hatch the nymphs will move to the swollen needle bases to feed and continue gall formation. The best time to control adelgids on both Norway and Colorado blue spruce is in late fall or early spring before adults mature and cover themselves with wax.

Last week the Douglas fir needle midge adults were beginning to emerge from beneath Douglas fir trees in Bucks and York counties. Eggs were found between the scales of the new buds. This week eggs have hatched and the midge larvae were found inside the needles. This insect was first found in Christmas tree fields in Pennsylvania in 2002. The window of opportunity for control of this insect appears limited. Eggs are laid soon after adults emerge followed by egg hatch within a couple of days. Larvae enter directly into the needles after hatching making contact with chemical difficult. Timing and effective chemicals to control this insect needs to be studied.