2026 Christmas Tree Scouting Report June 4, 2026

Weather Update and Growing Degree Days

Growing degree day accumulations continue to advance rapidly across Pennsylvania.The past seven days featured a mix of moderate temperatures, scattered rainfall events, and periods of elevated humidity across much of the state. These conditions supported continued shoot elongation, disease development, and insect activity. Many growers have now completed multiple fungicide applications targeting Swiss needle cast, Rhabdocline needle cast, and spruce needle cast diseases. In several locations, mature Douglas fir are beginning to harden off as new growth rapidly transitions from succulent tissue to mature foliage.

Looking ahead, temperatures are expected to climb significantly later this week, with daytime highs reaching the upper 80s and low 90s across portions of Pennsylvania. The return of summer-like temperatures is expected to accelerate scale crawler emergence, stimulate mite population growth, and advance bagworm development. Growers should pay particular attention to spider mite populations, which are beginning to reappear following the cooler spring weather. Warm, dry conditions can allow populations to increase rapidly, especially in Fraser fir and other susceptible hosts.

Douglas Fir Growth and Needle Cast Diseases

Many mature Douglas fir are beginning to harden off, marking an important seasonal transition. New growth is changing rapidly, and susceptibility to several needle cast pathogens is beginning to decline as shoots mature.

Several growers report completing three fungicide applications for needle cast diseases and spruce needle diseases. Continued monitoring remains important, particularly in areas that experienced frost damage,  prolonged wetting periods, but the highest risk period for new shoot infections is beginning to pass as foliage matures. Growers should continue evaluating new growth and monitoring for symptoms that may become apparent later in the season.

Elongate Hemlock Scale (EHS)

Elongate hemlock scale remains active in Fraser fir plantings. Eggs, crawlers, settled crawlers, and individuals beginning to develop protective coverings were observed this week. Some crawlers have already settled and begun covering over on needles, indicating that crawler emergence has been underway for several weeks.

The presence of multiple life stages suggests that emergence remains ongoing. Growers should continue inspecting the undersides of needles and monitoring crawler activity with tape traps or hand lens inspections. Management efforts remain most effective when targeting active crawler stages before protective coverings fully develop.

Where treatment thresholds warrant intervention, products such as dinotefuran (Safari) and pyriproxyfen (Distance) remain among the most commonly utilized options during crawler emergence periods. Thorough coverage of infested foliage is critical for successful management.

Cryptomeria Scale

The first cryptomeria scale crawlers of the season were observed this week in the York/Harrisburg region on Canaan fir. Egg hatch appears to be just beginning, and crawler emergence is expected to continue over the next two to three weeks.

Interestingly, no crawlers were observed on Fraser fir at this location despite active emergence on nearby Canaan fir. Differences in host species and site conditions can influence emergence timing, making block-by-block scouting especially important.

In Schuylkill County, no live cryptomeria scale stages were observed during this week's scouting. Growers with a history of infestations should continue monitoring closely as crawler activity is expected to expand across the region during the coming weeks.

Crawler emergence represents the most effective treatment window. Growers considering management should monitor closely over the next several weeks. Products commonly utilized for crawler suppression include pyriproxyfen (Distance), dinotefuran (Safari), and other labeled materials identified in the Pennsylvania Christmas Tree Pest Management Guide.

Spider Mites

Low populations of spider mites were observed on both old and current season growth of Fraser fir this week. Following the cooler weather experienced earlier this spring, mite activity appears to be increasing as temperatures warm.

With hot weather forecast later this week, growers should begin paying closer attention to mite populations. Warm, dry conditions favor rapid population growth, and infestations can develop quickly once temperatures rise. Scouting should focus on interior foliage and lower branches where populations often establish first.

Many growers reported good control of spider mites earlier this season. Continued monitoring will be important to determine whether populations remain below treatment thresholds as summer conditions develop. If treatment becomes necessary, growers should select products based on the life stage present and rotate modes of action to reduce resistance development. Common miticides used in Christmas tree production include abamectin (Avid), spiromesifen (Forbid), spirodiclofen (Envidor), bifenazate (Floramite), and hexythiazox (Hexygon), where labeled. Thorough coverage remains essential for effective control.

Eriophyid Mites

Small populations of eriophyid mites were also observed on Fraser fir. While often difficult to detect without magnification, these mites can contribute to needle distortion, bronzing, and reduced aesthetic quality when populations increase.

Growers should continue monitoring affected blocks and documenting symptom development throughout the season. As temperatures rise, populations may increase rapidly in susceptible plantings.

Balsam Twig Aphid

Balsam twig aphid populations appear noticeably lower than those observed during 2025. However, colonies remain easy to locate on current season growth, and second-generation winged adults are now present.

Most feeding injury associated with balsam twig aphid has already occurred during bud break and shoot expansion. At this stage, management of established populations is generally not recommended because treatment will not reverse existing damage. Instead, growers should evaluate infestation levels and beneficial insect activity to help guide management decisions for future seasons.

Syrphid Fly Larvae

Numerous syrphid fly larvae were observed feeding within balsam twig aphid colonies. These beneficial insects are important aphid predators and can consume large numbers of aphids during development.

The presence of syrphid fly larvae serves as a reminder of the value of conserving beneficial insect populations whenever possible. Adult syrphid flies also provide pollination benefits in agricultural and ornamental systems.

Aphid Midge Larvae

Aphid midge larvae were also observed actively feeding on balsam twig aphids. These predators attack aphids by injecting toxins that paralyze their prey before consuming internal fluids.

Although often overlooked during routine scouting, aphid midges can provide substantial biological control when populations become established. The presence of both aphid midge larvae and syrphid fly larvae within aphid colonies demonstrates strong beneficial insect activity across several plantings this season.

Bagworm

While bagworms have not yet been reported from Pennsylvania Christmas tree plantings, their arrival is likely approaching. Chris Kanarr of the Maryland Department of Agriculture reported finding early instar bagworms in Hurlock, Maryland during the last week of May.

Given current degree day accumulations and the warmer conditions forecast across Pennsylvania, growers should begin scouting susceptible hosts over the next one to two weeks. Newly hatched bagworms are very small and often go unnoticed. Early larvae construct protective bags from silk and pieces of host foliage, creating structures that initially resemble small needles attached to branches.

Common hosts include arborvitae, juniper, spruce, fir, and many ornamental landscape plants. Management is most effective when larvae are small. Products containing chlorantraniliprole (Acelepryn), Bacillus thuringiensis var. kurstaki (Btk), and spinosad provide effective control of young larvae when applied during early hatch periods. Once bags become larger later in the summer, control becomes increasingly difficult.

Clearwing Borers

Several growers are preparing treatments for clearwing borers in shade tree plantings this week. Adult flight activity has been reported in portions of Pennsylvania, and preventative applications are being timed to target newly hatched larvae before they enter host tissues.

Growers managing shade trees should continue monitoring traps where used and follow labeled recommendations for treatment timing.

Beneficial Insects

Beneficial insect activity continues to be an important component of integrated pest management programs this season. In addition to syrphid flies and aphid midges, growers should continue scouting for lady beetles, parasitoid wasps, lacewings, and predatory mites when evaluating pest populations.

Strong natural enemy activity may help explain reduced aphid populations in some blocks compared to previous years and can contribute significantly to natural suppression of several important Christmas tree pests.

Looking Ahead

The coming two weeks will represent an important transition period across Pennsylvania Christmas tree plantings. The anticipated warmup later this week is expected to accelerate development of several important pests.

Growers should prioritize monitoring elongate hemlock scale and cryptomeria scale crawler activity, as both species are entering vulnerable stages where management is most effective. Spider mites deserve particular attention as populations are beginning to reappear following the cooler spring weather. Hot, dry conditions can rapidly increase mite populations, making routine scouting especially important during June.

Bagworm hatch is likely approaching in Pennsylvania following reports of early instars in neighboring Maryland. Growers with susceptible hosts should begin scouting now for newly emerged larvae before bags become larger and more difficult to control.

As Douglas fir shoots continue hardening off, many spring disease management programs are nearing completion. This provides an opportunity to evaluate fungicide performance while shifting scouting efforts toward scale insects, mites, bagworms, and other summer pests. Continued observation of beneficial insects, including syrphid fly larvae, aphid midge larvae, lady beetles, and parasitoid wasps, will help growers assess natural biological control occurring within their plantings and may influence management decisions later this season.

The green giant arborvitae treated with Bravo Weather Stik, are starting to show improvement and pushing new growth.  Please share experience with us if you treated green giant arborvitae with chlorothalonil, or any other treatment methods. We do not have lab results back at this time, but hoping for an updated report next week. 

Next Report: 

We appreciate everyone who takes the time to share what they are seeing in their fields and beyond!

As always, growers should carefully read and follow the most current product label before making any pesticide application. Labels can change; rates may vary by crop or application method, and specific restrictions regarding PPE, reentry intervals, pollinator protection, and seasonal maximums must be followed. The Pennsylvania Department of Agriculture reminds applicators that "the label is the law" and that all pesticide applications must remain in compliance with both federal and state regulations.

The next scouting report will be available on June 10, 2026. Reminder, please submit observations anytime prior to Tuesday, June 9, 2026, by noon to Kelly Piccioni at keg200@psu.edu to be included in the next report. As a reminder, you may also call into the hotline weekly for updates: 1-800-PENN-IPM (1-800-736-6476) option 5