Christmas Tree Scouting Report: March 13, 2025

Greetings, readers, and welcome to the 2025 scouting season!

It's time to prepare for the 2025 growing season and the insect activity that will soon affect your Christmas trees. We are looking forward to bringing back the scouting reports growers depended on for so many years. Although they will look a little different, we are hoping to be able to share valuable IPM information to best assist the growers of Christmas Trees.

The scouting team of Kelly Piccioni, Don deMackiewicz, Cathy Thomas, Sarah Pickel, and several growers will soon be out placing traps for White Pine Weevil. We will also start calculating Growing Degree Days on March 1; this will indicate daily heat accumulation. We monitor GDDs via GDD Calculator, and you can custom track your temperatures by zip code.  Tracking with your own thermometers, average the daily maximum and minimum temperatures and subtract a base temperature of 50°F.

As the weather soon changes from winter to springtime,  GDDs will begin adding up. The pests we monitor each season have specific GDD ranges during which they typically emerge. Throughout the season, we'll provide updates on pest activity, life cycle details, and management options. While most of our reports will focus on the south-central Pennsylvania region, we will occasionally include updates from other parts of the state. If you are interested in contributing scouting information on any pest impacting raising Christmas trees, please email Kelly at keg200@psu.edu.

White Pine Weevil Monitoring

The scouting team has begun to set up white pine weevil traps at multiple locations. These traps are designed to lure and capture white pine weevils as they emerge from their overwintering sites in the needle litter beneath Christmas trees. White pine weevils are typically the first insect pests to become active in the spring, with activity expected between 7-58 GDD or when soil temperatures reach 50°F. They can be found either in traps or on tree leaders during this time. Adult beetles are about ¼ inch long, brown, and marked with white and rust-colored spots. They emerge in early spring, move to the tree leaders to feed, then mate and lay eggs inside the leaders. Evidence of weevil feeding includes small holes on the leaders,  and sap is often observed emerging from the hole.

White pine weevils cause leader dieback in host trees, including eastern white pine, other pine species, Serbian spruce, other spruce species, and occasionally Douglas-fir. If you have experienced white pine weevil damage on your farm in the past and want to monitor their emergence, trapping is the most effective method. Pyramidal traps, sold as Tedder's traps, can be purchased online from Great Lakes IPM. These traps need to be baited with separate vials of denatured alcohol and turpentine to function effectively. Traps should be placed in susceptible blocks now and checked several times a week.

If weevils are detected in traps, it's recommended to apply an insecticide to the top third of the trees immediately. If weevils continue to be caught in traps several days after the first application, consider making a second application 7-10 days later.  For more information, see the Penn State Extension factsheet on White Pine Weevil.

*Calculation via Greencast Online began March 1.
(please note, by the time of publication, we could have gained days with the warm temperatures)

In the chart at the top of this report, the GDD totals for select Pennsylvania locations will be updated weekly. Growers who want a more precise and up-to-date specific GDD total for their farm have a couple of options:

1. Calculate GDD manually using temperature data from a min/max thermometer on your farm. Detailed instructions are available here: GDD Calculation Guide.

2. Use an online tool or mobile app to track GDD by zip code. Free options include GreenCast Online and Cornell University's Growing Degree Days app.

GDD tracking typically begins on March 1st, but in 2024, colder temperatures persisted until this week, allowing only a few totals to accumulate. However, additional cold weather could slow progress. Growers should be prepared for conifer pests to become active quickly as temperatures warm. Monitoring and paying close attention to your own fields can help you to better determine when is the best time for you to spray on your own property. There have not been any observations of White Pine Weevils as of 3/11/25.  For more information about weevils, please check above as well as the factsheet: White Pine Weevil.

Eriophyid Mites

Growers may begin to see eriophyid mite activity on their trees in the coming weeks. These tiny pests are known as rust mites on spruces, firs, and hemlocks and as sheath mites on pines. Their feeding causes foliage to fade or take on a rusted appearance.

Look for overwintering eggs clustered on the undersides of needles near the base. These eggs range in color from salmon to off-white, while already hatched eggs appear transparent. The newly hatched, oblong mites—visible only with a hand lens—are off-white to peach in color and begin emerging within a GDD range of 7–22.

To scout for mites, check twigs with off-color foliage. If mites are present on 80% of the twigs sampled, treatment may be needed. Once the majority of eggs have hatched and there is no risk of freezing temperatures, growers can apply horticultural oil (before bud break) or a miticide labeled for rust mites.

For more details on this pest, visit the Penn State Extension spruce diseases fact sheet.

If you are seeing any pest activity on your farm, please let us know! Pictures are also welcome!  Contact Kelly at keg200@psu.edu.  

The next scouting report will be available on Thursday, March 20, 2025. We can anticipate activity as the temperatures will remain warm and night temperatures will be above freezing in the SE areas of PA.