March 22, 2006
Christmas Tree Scouting Report Number 2 - March 22, 2006
Since temperatures returned to slightly below normal early last week, there have been no white pine weevil adults found in any of the pyramidal traps in Bedford, Carbon, Columbia, Dauphin, Juniata, Perry, Schuylkill, or York Counties. A grower from Juniata County reported 22 Growing Degree Days (GDD) and growers from Schuylkill County were reporting 27 to 36 GDD as the temperatures briefly climbed into the low 80s early last week. Growing Degree Day accumulations for adult spring emergence range from 7-58 (base 50). In Schuylkill Co. in 2005, white pine weevil adults began to emerge with accumulations of ~5 GDD on April 1st. Weevil activity probably won't resume until daily temperatures average above 50 degrees F.
If you had damage last year from the Cooley spruce gall adelgid you can now begin scouting for over wintering nymphs on Colorado blue spruce and Douglas fir. On Colorado blue spruce the tiny, black nymphs feed around the buds, and are easily spotted if you examine the twigs with a hand lens. Nymphal feeding causes the tips of the new growth to swell and curl downward. On Douglas fir, the nymphs feed on the undersides of the needles, where they cause chlorosis and kinking of needles. On Norway spruce it is the eastern spruce gall adelgid that form the galls at the base of the new growth and cause tip die back. As the weather warms these nymphs continue to mature, and produce a protective wax covering. The best time to control these pests is either in the fall or early spring when the nymphs are still exposed.
Overwintering eggs of the Balsam twig aphid can be found on the bark of twigs. This is a pest of “true firs” or Abies spp. Look between the needles for tiny, oval eggs covered with silvery threads of wax. These eggs begin hatching as early as the last week in March. These aphids or “stem mothers” begin to produce live young when buds begin to open. Feeding damage by the maturing young aphids cause the new needles to twist and distort in shape. Control toward this aphid is best when the majority of eggs have hatched but before new buds open.
Eggs of the spruce spider mite can be found on the bark and at the base of the underside of needles when twigs are examined with a hand lens. Begin by looking for discoloration at the base of needle surfaces and then salmon to red colored eggs on the underside of twigs. Feeding by spruce spider mites cause plant cells to die turning shoots a yellowish to rusty-brown color and can be found damaging all Christmas tree species. Dormant oil can be applied when temperatures are above 40 degrees F, and there is no danger of freezing before spray dries. Otherwise a registered miticide or insecticide labeled for mite control can be used once mites begin to hatch about mid April.
Another mite known as eriophyid mites or “rust mites” can give Colorado blue spruce and Norway spruce a washed out or bleached look to the needles. To scout for this mite in early spring look for that off color then examine bottom of needles for very tiny salmon color eggs. Like the spruce spider mite, these too are known as cool season mites that will begin hatching very soon. Remember dormant oil will remove blue bloom from glaucous trees. Occasionally rust mites can cause damage on Concolor firs as well.