Christmas Tree Scouting Report: April 3, 2025

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

Pest Information

Balsam Twig Aphid

A common pest of true firs was observed in southern York County this week. There have not been any aphids found in Schuylkill or Berks Counties this week. Stem mothers of balsam twig aphid were active on Fraser fir. The hatching of these first-generation aphids typically occurs within the range of 30-100 GDD. These aphids have hatched from the overwintering eggs. There were still some eggs found to be unhatched. The newly hatched stem mothers will feed on last season's needles. This feeding doesn't cause much damage, but when bud break of firs begins, these stem mothers will give birth to nymphs that will enter the opening buds and begin feeding on the newly expanding needles.  This feeding will cause the needles to curl and this damage is not reversible.

When scouting for the balsam twig aphid, a hand lens is necessary. The overwintering eggs will be found on the twigs, tucked in at the bases of needles. They will most commonly be found on the outer two inches of growth and on undamaged twigs located next to twigs with damage. The eggs are football-shaped and covered in fine silver filaments. The stem mothers that hatch from these eggs are pale green, wingless, and waxy.  They often will have a clear bubble of 'honey dew' or excrement at their posterior. If growers are having difficulty finding aphids on the foliage, an easy scouting technique is to hold a paper plate under symptomatic foliage and tap the foliage to dislodge any hatched aphids onto the plate. A hand lens will be helpful to see aphids moving on the plate.

To prevent damage from this pest, growers who have had damage in the past should apply a horticultural oil or insecticide after most of the eggs have hatched, but before bud break.

White Pine Weevil Monitoring

White pine weevils were found in multiple traps this week in York County, Berks County and Schuylkill County. Most locations in Pennsylvania are beyond the 7-58 GDD starting range for adult weevil emergence. Another indicator for the emergence of this pest is ground temperatures. When soil temperatures rise above 50°F, these weevils will begin to be found. This week temperatures collected in Berks, Dauphin, York, Cumberland and Schuylkill, the soil temperatures had risen above 50°F. Growers can expect to be finding weevils in their traps as this week's temperatures continue to warm up. There have not been feeding adults on the leaders of these trees yet, so growers must determine when the best time to spray. It is recommended that insecticide be applied when those adults are actively feeding to gain the most control.  For growers who are using the pyramidal traps (Tedder's traps available at Great Lakes IPM) to monitor for white pine weevil, it is important to remember to keep the bait vials filled with ethanol and turpentine. These attractants are essential in drawing the weevils into the traps, but the ethanol will eventually evaporate if not regularly refilled.

Growers who are not trapping for this pest may still be able to see weevils in their fields. On warm, sunny days like we have had this weekend, weevils may be found on leaders of host trees feeding on sap or mating. Those trees are pines, especially eastern white pine, spruces, especially Serbian, and occasionally Douglas-fir. These weevils are approximately ¼ inch in size and are brown in color, with white and rust-colored spots on the lower portions of their wing covers (or elytra). After emerging and moving to the leaders of the trees, the weevils will feed and mate for a while, but after about a week, they can begin to lay eggs in the leader. After this happens, the damage will be inevitable, so it is important to make any pesticide applications before egg laying begins or in less than a week after weevil emergence on your farm. Insecticides can be applied to the top third of the trees. If weevils continue to be found in traps several days after the first application, growers may want to consider making a second application 7-10 days after the first.

For more information on white pine weevil see the Penn State Extension factsheet on white pine weevil.

Eriophyid Mites

In Schuylkill and York Counties, hatched Eriophyid mites (also called rust mites) continue to be found on the foliage of Colorado blue spruce. These mites may have begun emerging a few weeks ago, as the GDD range for the start of egg hatch is 7-22.  The activity of these cool-season mites peaks in the spring and decreases as the warmer temperatures of summer arrive. A lot of foliage damage can occur within that peak cool season activity. Look for twigs that have a rusty or gray discoloration. When scouting, check the top third of your trees, pulling needle clusters on the southeast side of the tree.  Be sure to check trees from a variety of locations within the block of trees. Damage will appear like small scratches running parallel with the midrib of the needle. This damage is caused by the rust mites sucking on the plant fluids. Hatched mites are somewhat cone-shaped and will be peach or off-white in color. A hand lens is needed to see both the mites and the overwintering eggs, which are even smaller and will be clustered together on the undersides of needles, very close to the needle bases. Eggs are salmon-colored or off-white.

If mites are found on 80% of the twigs sampled, then a control action may be necessary. When most of eggs have hatched (hatched eggs will be transparent) and there is no risk of freezing temperatures, growers can apply a horticultural oil (prior to bud break) or a miticide with rust mites listed on the label.  It is important to spray when you find active mites. It isn't advisable to apply a horticultural oil to blue spruce because it can affect the blue coloration. Scout again within four weeks to determine if a follow spray of a miticide or horticultural oil is required.

Key Upcoming Activity to Monitor

Douglas Fir

Prep for the early signs of bud break: swelling and lightening in color, with just a very small percentage (1%) showing a slight opening at the tip. Growers should keep a close eye on these buds over the next week and be prepared to make their fungicide applications for Rhabdocline and Swiss needle cast diseases and insecticide applications for Douglas-fir needle midge. No midges have been found in traps at this time.

Concolor Fir

Phyllosticta and Pythium Root Rot have been found on samples sent for testing, and Phyllosticta is often found on concolor but also associated with plants that are stressed due to poor soil conditions and root problems. Several of the rapidly declining Concolor were dug, and the presence of "J" roots was observed. Due to the severe drought conditions, partnered with the taproot root system, this would be the leading environmental probable cause of early death. Pruning and removal of dead and decaying branches is recommended. Pythium Root Rot can be treated with fungicides containing etradiazole or other drenches containing phosphorus acid salts is recommended. Note that if soil draining or poor soil moisture conditions remain, the fungicide may not be effective.

Visit the Penn State Plant Disease Clinic for Information about testing

 The next scouting report will be available Thursday, April 10, 2025