2026 Christmas Tree Scouting Report May 21, 2026

Weather Update

The past week brought significant swings in weather conditions across much of Pennsylvania, including several days of unusually high temperatures, strong sun intensity, and periods of drying conditions. Many growers experienced rapid drying of soils and tender new growth, along with increased plant stress on recently flushed trees and arborvitae. The heat also caused some growers to delay fungicide applications, particularly chlorothalonil products and other protectant sprays, out of concern for potential phytotoxicity or stress to tender foliage during extreme temperatures.

While the recent warmth helped accelerate degree day accumulation and insect development, the forecast moving ahead appears to shift toward cooler temperatures, higher humidity, scattered rainfall, and more prolonged needle wetness periods. These changing conditions may create increasingly favorable environments for fungal pathogens such as Rhizosphaera, Stigmina, Swiss needle cast, Phyllosticta, and Pestalotiopsis, particularly in stressed or historically susceptible plantings. Warm, wet conditions combined with extended leaf and needle wetness periods can significantly increase spore production, spread, and infection potential.

Growers should continue monitoring weather patterns closely over the coming week and be prepared to resume protective fungicide programs as temperatures moderate and application conditions improve. Upcoming moisture may also improve efficacy and uptake of certain systemic products while supporting continued flush and root activity in actively growing trees. Careful attention to spray timing around rainfall events, humidity levels, and plant stress conditions will remain important as the season transitions from heat stress into a potentially favorable disease development period.

Pest Information 

Elongated Hemlock Scale 

Elongate hemlock scale activity is increasing across several regions of Pennsylvania. In untreated small Fraser fir at approximately 420.5 GDD, eggs and crawlers were found beneath scales, though crawler movement onto needles has not yet been widely observed. York County observations also noted EHS crawlers were present on Fraser fir, indicating active development is underway in some blocks. Mature treated Fraser fir plantings showed little to no active EHS pressure, suggesting earlier management programs remain effective in managed blocks. Growers should continue carefully scouting the undersides of needles and beneath scale covers over the next 1 to 2 weeks as crawler emergence progresses.

For growers currently seeing relatively low elongate hemlock scale populations, it may be worth considering whether scale applications can be timed closer to anticipated cryptomeria scale crawler emergence in early June. In several monitored plantings, cryptomeria scale eggs are developing rapidly, though crawlers have not yet emerged. Delaying treatment slightly may allow growers to better target multiple scale species during a more vulnerable life stage while potentially reducing the number of applications needed.

Beneficial parasitoid wasps attacking cryptomeria scale were also observed actively working in the field this week. These naturally occurring beneficial insects lay eggs within scales, where developing larvae consume the scale insect from the inside before emerging to continue parasitizing additional scales throughout the planting. Preserving these beneficial populations may provide valuable long term biological suppression of scale pests. Reports from the field noted interest in products such as Movento, which may offer scale management while being less disruptive to beneficial parasitoids compared to some broad spectrum insecticides. As always, growers should carefully review current label directions, timing recommendations, and rotational considerations before making management decisions.

Needle Casts 

Swiss needle cast fruiting bodies are easy to find on Douglas fir trees at this time. Look on the undersides of the needles for the black dots in rows.

Recent periods of unusually high temperatures have caused some growers to delay fungicide applications for spruce needle cast diseases, including chlorothalonil products such as Bravo and other protectant fungicides. Applying certain fungicides during periods of extreme heat may increase the risk of phytotoxicity or plant stress, particularly on tender new growth. However, the combination of recent heat followed by forecasted humidity, rainfall, and prolonged needle wetness periods may create favorable conditions for fungal disease development and spore spread. Diseases such as Rhizosphaera, Stigmina, and Swiss needle cast often spread rapidly during warm, wet conditions where needles remain wet for extended periods. Growers should continue monitoring weather patterns closely and resume protective fungicide programs as temperatures moderate and application conditions improve. Careful timing around upcoming rain events may be especially important for protecting susceptible spruce and Douglas fir blocks during this infection period.

Cryptomeria Scale 

In many scouting areas across the state, Cryptomeria scale eggs are now present beneath scale covers in monitored plantings, although crawlers have not yet emerged. Based on current development and weather conditions, crawler emergence may begin in early June. Winged Males have been observed flying. Beneficial parasitoid wasps actively attacking cryptomeria scale were also observed this week. These beneficial insects naturally suppress scale populations by laying eggs within scales, where developing larvae consume the host insect. Preserving beneficial populations may improve long term biological suppression of scale insects. Begin and continue scouting, flag areas and be prepared to spray once crawlers emerge. Based upon your pest pressure, your choice of treatment will vary.  As mentioned above, Movento is a good choice to protect beneficials like a parasitic wasp that lays its eggs inside of Cryptomeria scale. 

Parasitoid wasps are one of the most important natural enemies helping suppress cryptomeria scale populations in Christmas tree plantings. These tiny beneficial wasps are often so small they go unnoticed in the field, but they can play a major role in reducing scale pressure over time, especially when broad spectrum insecticide use is limited.

The adult female wasp locates cryptomeria scales on needles and lays her eggs directly inside or beneath the scale covering. Once the parasitoid larva hatches, it feeds internally on the scale insect, eventually killing it from the inside. After development is complete, the new adult wasp emerges and searches for additional scales to parasitize, continuing the cycle throughout the planting.Growers sometimes notice evidence of parasitoid activity as darkened or hollowed scales, or small emergence holes in old scale covers. In fields where beneficial populations are established, they can provide meaningful natural suppression and may help slow rapid scale population increases.

Because these beneficial insects are highly sensitive to many broad spectrum insecticides, preserving them can be an important part of an integrated pest management (IPM) program. Softer chemistries and carefully timed applications may help maintain parasitoid activity while still managing damaging scale populations. Therefore products such as Movento are often discussed in these situations because they may be less disruptive to beneficial parasitoids compared to some contact insecticides, though growers should always follow current label directions and treatment recommendations.

Balsam Twig Aphid 

Balsam twig aphid feeding injury was observed in untreated young Fraser fir blocks, although both populations and damage levels appear significantly lighter than last season in many monitored areas. At this stage of the season, treatment timing for BTA is generally considered past optimal, as much of the visible damage is already set for the year. The most effective treatment window occurs shortly after overwintering eggs hatch and just before bud break, when newly emerging aphids are most vulnerable. Once feeding damage and needle distortion become visible, sprays provide limited benefit for improving current season appearance. While some systemic materials may reduce portions of the remaining aphid population, they are unlikely to reverse existing injury and may not be the most effective approach in Fraser fir blocks where scale management is also a concern. In many situations, growers may achieve better overall results by focusing management efforts on emerging scale crawler timing rather than attempting late season BTA suppression. In a high infested area, Larvae of Asian lady beetle were also found in high numbers, along with syrphid fly larvae. 

Asian lady beetles and syrphid fly larvae are both important beneficial predators commonly found in areas with balsam twig aphid (BTA) activity. Their presence in Fraser fir plantings is often a positive sign that natural biological control is helping suppress aphid populations.

Asian Lady Beetle adults and larvae are aggressive aphid predators that actively feed on balsam twig aphids throughout the growing season. Both life stages consume soft-bodied insects, with larvae often eating large numbers of aphids as they develop. Adult beetles are highly mobile and tend to move into blocks where aphid populations are increasing. While growers sometimes think of Asian lady beetles primarily as nuisance insects around homes in the fall, in Christmas tree plantings they can provide meaningful aphid suppression.

Syrphid fly larvae, sometimes called hoverfly larvae, are another highly beneficial predator frequently observed in aphid populations. Adult Syrphid Fly resemble small bees or wasps and are important pollinators, but it is their larvae that provide pest control benefits. The larvae are legless, slug-like predators that feed voraciously on aphids by grabbing and consuming them individually. Syrphid larvae are often overlooked because they blend well into foliage and move slowly, but they can dramatically reduce localized aphid populations.

The presence of both Asian lady beetles and syrphid fly larvae in BTA-infested Fraser fir blocks suggests beneficial insect activity may already be contributing to the lighter aphid pressure observed this season in some areas. Preserving these predator populations through careful insecticide selection and application timing can be an important part of an integrated pest management (IPM) program. Broad spectrum insecticides applied after natural enemies are active may reduce beneficial populations along with the target pest, potentially allowing aphid populations to rebound later.

Bag Worms

Bagworms have not yet been observed in monitored Christmas tree plantings this season, but now is an important time for growers to begin scouting and reviewing historical problem areas before hatch begins. Bagworms can become serious pests on spruce, fir, arborvitae, juniper, and other conifers, especially in blocks bordering hedgerows, windbreaks, buildings, or unmanaged landscape plantings where populations often establish unnoticed.

Bagworms overwinter as eggs inside the protective bags left behind by females from the previous season. Each bag may contain several hundred eggs. Hatch typically begins from late May through June depending on local temperatures and weather conditions. Newly hatched larvae are extremely small and often disperse by “ballooning” on silk threads carried by the wind, allowing infestations to spread quickly across fields and neighboring plantings.

Early feeding can be difficult to detect because young larvae remain very small and often feed within interior foliage first. Initial symptoms may appear as light browning, windowpane feeding, or thinning foliage before bags become obvious later in the summer. As larvae grow, they construct the familiar spindle shaped bags from needles and plant material, enlarging them throughout the season. By late summer, mature larvae pupate within the bags and females remain inside after mating to lay overwintering eggs.

Growers should begin weekly scouting now in historically infested blocks and around field edges, arborvitae plantings, spruce blocks, and nearby ornamental hosts. Carefully inspect branches for old overwintering bags, feeding injury, and newly emerging larvae. Early detection is critical because smaller larvae are significantly easier to manage than mature bagworms later in the season. Monitoring now can help growers better time treatments if populations begin developing in the coming weeks.

When scouting, look closely along interior foliage and branch tips for:

• Tiny moving "needle cases" attached to foliage
• Windowpane or skeletonized feeding on needles
• Small silk threads from ballooning larvae
• Old overwintering bags nearby from last season

The ideal treatment window is when larvae are still under about 1/4 inch long and actively feeding. Bt, spinosad, Safari, and Acelepryn are safer options for beneficial insects. 

Spider Mites

Growers are reporting significantly lighter spruce spider mite pressure this season compared to recent years, with some fields showing very low populations and minimal feeding injury so far. In several monitored blocks, growers noted that previous management efforts appear to be providing good control heading into the warmer portion of the season. Continued scouting is still important, however, as hot, dry weather can allow mite populations to increase rapidly over a relatively short period.

Some growers may also be seeing the benefits of improved timing, rotational chemistry programs, and increased preservation of beneficial insects and predatory mites within their plantings. Avoiding unnecessary broad-spectrum insecticide applications can help conserve many naturally occurring predators that assist with long-term mite suppression. Predatory mites, lady beetles, lacewings, and other beneficial arthropods often play an important role in keeping spider mite populations below damaging levels when environmental conditions are favorable.

As temperatures rise moving into late spring and early summer, growers should continue monitoring interior foliage and lower branches for stippling, bronzing, webbing, and active mites using shake tests or hand lens inspections. While current pressure remains low in many areas, extended periods of hot, dry weather may still favor rapid population development later in the season, particularly in stressed trees or historically infested blocks.

Arborvitae- Winter damage and opportunistic fungal infections 

Several growers are reporting prolonged winter injury symptoms on Green Giant arborvitae this spring, including scattered bronzing, tip dieback, interior browning, and decline on stressed foliage. In a number of cases, there is suspicion that opportunistic fungal pathogens such as Phyllosticta Needle Blight and Pestalotiopsis Tip Blight may be colonizing tissue already weakened by winter stress, fluctuating temperatures, desiccation, or root stress from the past season.

Current observations suggest that much of the initial injury may have originated from environmental stress rather than primary pathogen infection alone. Opportunistic fungi, such as Pestalotiopsis, are commonly associated with stressed arborvitae and can invade damaged tissue following winter burn, drought stress, mechanical injury, transplant stress, or other environmental challenges. Phyllosticta may also develop on weakened foliage and contribute to additional needle browning and spotting under extended wet conditions.

Nick Brazee from UMass Extension Plant Diagnostic Lab has emphasized the importance of first addressing underlying plant stress and environmental conditions when managing these issues. Recommendations include improving airflow where possible, avoiding overhead irrigation during prolonged wet periods, pruning and removing heavily infected tissue when practical, and maintaining overall tree vigor through proper watering and cultural management. Similarly, recommendations from Michigan State University Extension note that Pestalotiopsis is frequently acting as a secondary invader following winter injury or environmental stress events rather than as an aggressive primary pathogen in otherwise healthy plants.

Samples from affected Pennsylvania plantings are currently being confirmed through the Penn State Plant Disease Clinic to better determine the pathogens involved and the extent of fungal activity. In the meantime, some growers elected to apply Bravo Weather Stik to Green Giant arborvitae while already making fungicide applications for needle cast management in Douglas fir blocks. While fungicide applications may help protect healthy foliage from further fungal colonization during favorable disease conditions, management success will likely depend heavily on reducing underlying stressors and promoting plant recovery going forward.

In addition, Emerald Green Arborvitae, both in nursery settings and more so in landscape settings, are showing signs of fast-moving declines.  Material tested last summer showed infections of both of these fungi. We will update with confirmed findings of the most recent samples. 

The Next Report:

Growing Degree Days have accumulated quickly this week.  Next week looks cooler and hopefully with some rain. Stay vigilant in scouting and contact Kelly at keg200@psu.edu with any questions or to share observations.  We have been getting more information throughout the state, which has been helpful in sharing a more comprehensive 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 May 28, 2026. Reminder, please submit observations anytime prior to Tuesday, May 26, 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.