Christmas Tree Scouting Report: March 27, 2025

Weekly scouting report compiled by Kelly Piccioni, Penn State Extension. This week's scouting data contributors: Kelly Piccioni, Penn State Extension, Don deMackiewicz, Sarah Pickel and Cathy Thomas (Pennsylvania Department of Agriculture), Jim Fogarty (Schuylkill County).

Pests

White Pine Weevils

Weevils were found in very low numbers this week in Berks County traps set amongst Serbian Spruce. Soil temperatures were measured at 52 degrees where these weevils were found. In other traps in Berks set amongst White Pine, soil temperatures are still in the 40s, and no weevils have been found. In Schuylkill County, the soil temperatures remain in the mid 40s as well. To read more about white pine weevils, reference last week's report: March 20, 2025 scouting report  Scouters should be vigilant in checking traps and taking various temperatures throughout their fields. Different blocks may be active sooner than other blocks, such as blocks with smaller trees where there is more exposed soil compared to larger trees that is harder for the sun to penetrate.

The emergence traps attract brown-mottled adult beetles after they have emerged from their overwintering sites. After emergence, they will feed and mate. The hope is that an insecticide application will be made within 7 days of this emergence to prevent the adult weevils from laying eggs inside the host tree leaders. Once the eggs are protected within the leader, they will hatch into larvae that feed on the leader's vascular tissue. It is the larval feeding that eventually kills the leader. If the opportunity is missed to kill the adults with an insecticide application, the infested leaders can be cut out and burned/removed from the fields before the developing weevils have a chance to emerge mid- to late July. The cutting should be made down in the green, healthy tissue to ensure that all the developing weevils are removed.

Spruce Gall Adelgids

These adelgids are now covered in a white, cottony wax, whereas two weeks ago, the small black adelgids were still somewhat exposed. This waxy covering provides protection, making insecticide applications ineffective from this point forward. Preventative insecticide treatments should have been applied a few weeks ago. The protected adelgids will soon lay dozens of eggs beneath their coverings, which will hatch and begin feeding on emerging Norway spruce buds. This feeding leads to the formation of a pineapple-shaped gall at the base of new growth, which can be unsightly and potentially hinder tree development. This process is similar to the effects of the Cooley spruce gall adelgid on Colorado blue spruce. However, the Cooley spruce gall adelgid also affects Douglas-fir, where it causes needle kinking instead of gall formation.

The most effective time to control spruce gall adelgids is in the fall when they have settled into their overwintering sites at the base of next season's buds and are exposed to the elements. At this stage, they lack their protective waxy covering. When scouting for this pest, check branches adjacent to those already damaged by galls for the presence of adelgids.

Eriophyid Mites

In York County on Tuesday morning, active, hatched Eriophyid mites were found moving on Norway Spruce. These tiny mites attack not only firs, hemlocks, and spruce but can also be found on pines. When scouting, look for small, round eggs clustered on the lower portion of the needles near the twig. The narrow, triangular-shaped mites can be seen moving along the needles. On spruce, both the eggs and mites appear peach or salmon-colored, while on firs and hemlocks, they are white or translucent. Hatched eggs on any host appear clear. Growers should consider treatment with horticultural oil or insecticide if mites are present on 80% of the sampled twigs. Remember that use of horticultural oil on blue spruce (Picea pungens) can cause temporary color loss. 

Balsam Twig Aphid

Balsam twig aphids are strictly a pest of true fir species such as Fraser fir, Canaan fir, Concolor fir and others. The damage these tiny, soft-bodied pests cause is a twisting of the new growth. This twisting does not kill the new growth, but the twisting will not go away. 

Balsam twig aphids overwinter as eggs on the underside of the current season's twigs. When GDD falls within the range of 30-100, gray-green nymphs will hatch from these overwintering eggs. When scouting for this pest, look for eggs on last season's stems that are close to symptomatic twigs, but not showing damage themselves. The aphids will begin feeding on the undersides of the needles. A tip to find these nymphs is to tap the upper side of branches over a white paper plate or piece of paper. The aphids will appear green and plump. These aphids mature to become stem mothers or reproductive females, which will produce the next generation of aphid nymphs. As soon as the season's new buds begin to break, those nymphs will crawl in and begin feeding on the new, tender needles. This feeding causes the irreversible, twisting damage. To prevent this damage from occurring, a control application of a horticultural oil, insecticidal soap, or insecticide should be applied after the majority of eggs have hatched, but before the buds begin to break.

Douglas Fir Midge

Douglas Fir Midge Traps have been set in Schuylkill and York Counties. Traps can be made from plastic recycling bins, wax-coated cardboard boxes, clear empty jars with dry, crumpled paper towels to detect emerging adults. Boxes should be placed on the north side of the tree known to have previous damage. A picture of the traps can also be found in last week's guide as well as in the Christmas Tree IPM Guide. The Douglas-fir needle midge is a small, mosquito-like fly whose larvae mine needles, causing yellowing, distortion, and defoliation. The pest overwinters in the soil as pupae, with adults emerging around budbreak in spring to lay eggs on new growth. Larvae feed throughout the summer before dropping to the ground to pupate, completing one generation per year. Integrated Pest Management (IPM) strategies emphasize non-chemical controls, including pruning heavily infested branches, using emergence traps to capture adults, and scouting for early detection. Chemical control, if necessary, should target adults during budbreak, using pyrethroids or acephate, with multiple sprays applied within one week of the first catch and again after ten days. The scouters will continue monitoring these traps throughout the growing season.

We are in the process of setting up the IPM Hotline at 1-800 PENN IPM (1-800-736-6476). For Christmas trees, you will press 5. Those updates will hopefully start next week. If you are seeing anything on your farms and would like to contribute to the weekly scouting reports, please email pictures and information to Kelly at keg200@psu.edu. The next scouting report will be available April 3, 2025.