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April 18, 2007

Christmas Tree Scouting Report #4 - April 18, 2007
Weekly newsletter compiled by Sandy Gardosik, PA Department of Agriculture.

The unusually low temperatures we have been experiencing is slowing insect activity in the field. Temperatures are expected to get back on track within the next week, so get ready for spring because here it comes I hope.

No white pine weevils were found in traps in Perry County this week. Terminals of white pine from Berks County, exhibiting feeding damage were examined for eggs, but none were found. Since the white pine weevils began to emerge three weeks ago, I would have expected female weevils to begin ovipositing or laying eggs, had this been a normal year.  It will be interesting to see if there will be a second surge of weevils as temperatures warm. Some growers only sprayed once when weevils first began to emerge from their overwintering sites at the end of March, and they are hoping not to find weevils in traps as the weather warms, as this may warrant a second spray.

Spruce spider mite eggs have not begun to hatch on Fraser fir in Berks or Dauphin Counties. Historically, spruce spider mite eggs have hatched as early as the first week in April, but on average hatch begins in mid- to late April. Using a handlens, begin scouting where you noticed damage in previous years by examining the undersides of twigs for round red eggs on the bark, between needles, and around the buds. In the next week or two, you should check for egg hatch by tapping a branch over a white surface and looking for small fast-moving dots that squish red.

Cooley spruce gall adelgids on Colorado blue spruce in Berks County were covered with long waxy white threads but no eggs were found. The best control is achieved before the long wax fibers form over the adult females.  In Dauphin and Schuylkill counties the Cooley spruce gall adelgids on both Colorado blue spruce and Douglas fir were still exposed, with little wax forming around and over top of the developing nymphs.

Growers in the southeast counties, who are planning on spraying for the Douglas Fir Needle Midge (DFNM), should have emergence traps set under Douglas fir trees that were infested last year. Growers further north should plan on putting traps out during the next week (April 23rd-28th). For best control of this midge, it is essential to know when the adult midges emerge from the soil beneath Douglas fir at your particular farm.  Chemical controls are directed at the adults, before their eggs are laid. Emergence traps for the DFNM can be constructed with minimal materials and time: a 12" x 12" cardboard box, four rocks, and a plastic peanut butter jar. Turn the box upside down so the open flaps are down. Cut a hole that is slightly smaller than the lid of jar in one of the sides near the taped flaps, then screw the jar into the hole. Place the trap under a tree that was infested the previous year, then flip the flaps out and place a rock on each one so the box stays secure under the tree. Adult midges that emerge beneath the box fly to the light at the jar and collect there. Midges are small flies with long legs and antennae and orange bodies.  Adult midges mate, and females lay eggs within 2-3 days of emergence so the window for chemical application is limited. Adults emerge when buds swell and just begin to break. Eggs are elongate, orange, and can be found between newly expanding needles and bud scales. They hatch in a couple days, and larvae bore directly into the needle, making chemical control impractical at this stage. Once larvae are inside the needle, they will feed and grow there until they mature. In late November to early December, the mature larvae chew a small exit hole in the bottom of the needle and drop to the ground where they will overwinter. Damage caused by the DFNM feeding turn needles yellow to brown as the larvae grow. The needles are frequently bent and distorted by the larval feeding, and damage can be sufficiently heavy and cause enough early needle drop and make trees unsaleable. Check the PA Christmas Tree Pesticide Recommendation Sheet for control recommendations. Spraying before bud break with a long-residual insecticide should give the best control because the adult midge is your target, and egg-laying occurs soon after they emerge.