2026 Christmas Tree Scouting Report May 7, 2026

Weather Update 

The past week brought a mix of warm temperatures, cooler nights, scattered rain events, and slower than expected growing degree day accumulation across many regions of Pennsylvania. While some northern and elevated sites only gained around 13 GDD during the week, warmer southern areas such as Dillsburg reached approximately 352 GDD year to date, with soil temperatures approaching 59°F and daytime highs climbing into the low 80s.

Looking ahead, forecasts continue to call for alternating warm periods followed by cooler, wet stretches. This pattern favors continued disease pressure, prolonged needle susceptibility, and staggered insect emergence timing. Growers should expect pest activity to continue increasing steadily, especially following warmer periods and rainfall events.

Frost Damage 

Frost damaged new growth can become more susceptible to both insect injury and needle cast diseases, although the level of risk depends on the severity of the damage and weather conditions that follow.

When tender expanding shoots are injured by frost, the damaged tissue becomes stressed and often develops cracks, distorted growth, or slowed hardening of the new needles. That stress can make trees less resilient overall and may prolong the period that young needles remain vulnerable to fungal infection. In Douglas fir especially, frost slowed or uneven shoot elongation can extend the susceptibility window for Swiss needle cast and Rhabdocline because the new needles stay tender longer than normal.

Frost injury can also complicate scouting because damaged tips may initially resemble disease symptoms or insect feeding. Blackened or curled shoots, water soaked tissue, and stalled elongation can sometimes be confused with midge injury or fungal blight.

From an insect standpoint, stressed trees often become more attractive or less tolerant to certain pests. Delayed growth may overlap longer with Douglas fir needle midge activity, and damaged buds or shoots can reduce the tree’s ability to outgrow feeding injury. However, frost itself does not directly “cause” insect infestations.

A good scouting approach after frost events is to:

• Revisit damaged blocks several days later as symptoms fully develop.
• Monitor whether new growth resumes normally or remains stalled.
• Continue fungicide protection on susceptible new needles if elongation continues.
• Avoid assuming all distorted growth is frost related, especially where pest pressure already exists.

This year especially, with rapid early development followed by temperature swings, growers should expect some overlap between frost symptoms, disease pressure, and insect activity. Frequent scouting remains critical.

Per Stephanie Shirk, Director of Agriculture Business Development Center, PA Department of Agriculture: "In Monday morning's USDA/PDA stakeholder virtual roundtable hosted by PennAg Industries, we have identified pain points and action steps to take. One of those steps is to encourage all producers, regardless of crop and availability of crop insurance, to be in touch with the Farm Service Agency to elevate awareness of how the freeze has affected your operation. When disaster declarations are enacted, the process begins with the Farm Service Agency. PA Farm Bureau is also conducting a survey to better understand the impact. 

Pest Information

Douglas Fir Needle Midge 

Douglas fir needle midge flight activity continues across much of the state, although trap catches are beginning to decline in several locations. A few adults were still captured this week, confirming continued activity, but overall emergence appears to be tapering off in many southern and central regions.

Many growers have already made insecticide applications targeting adults and newly emerging larvae. However, blocks with historically heavy pressure should continue to be monitored closely, especially in cooler sites where emergence may still be ongoing.

Continue checking box traps or sticky traps weekly to monitor ongoing Douglas fir needle midge activity, especially in cooler or higher elevation sites where emergence may be prolonged. Pay close attention to interior and lower branches, as these areas often experience the heaviest pressure first. As the season progresses, watch for yellowing, curled, or distorted needles that may indicate developing larval feeding injury. With recent cooler weather patterns slowing development in some regions, growers should continue scouting carefully even if activity appears to be declining in warmer areas.

Needle casts

Needle cast diseases remain a top priority statewide. New growth is continuing to elongate across many Douglas fir blocks, and newly emerging needles remain highly susceptible to infection during this period.

Many growers have completed first fungicide applications and are continuing follow-up sprays. Intermittent rainfall, extended moisture, and fluctuating temperatures are creating favorable conditions for continued disease development. Protective coverage remains critical as long as new needles continue expanding. Infection risk begins around budbreak and continues through early needle elongation, generally between 200 and 300 growing degree days, particularly under wet conditions.

Trees in Southeastern Pennsylvania are at 100% bud break and have several inches of new growth at this point. We have had several days of welcomed rain, and temperatures are rising; the perfect environment for needle cast to sporulate so be timely with applications for maximum control. Spray fungicide when new growth is ¾-inch and again 3 weeks layer. The needle cast diseases of spruce, Rhizosphaera and Stigmina, will also be ready to release spores to infect the newly emerging buds.  Rhizosphaera affects Colorado blue spruce and Engelmann spruce and Stigmina infects Colorado blue spruce, black spruce and Serbian spruce.

The signifying symptoms of these diseases are brown or discolored needles on the lower branches which exhibit tiny, black fruiting bodies pushed out through the stomates on the undersides of the needles. Growers dealing with rust should begin fungicide applications to the spruce foliage when the new buds have begun to break. Additional applications can be made weekly and should continue until the new needles harden off or the old infected needles are cast. This should also be followed if both rust and needle cast diseases are present. The recommendations for needle cast suggest a 2-3 week interval between applications, although if the season is rainy, that interval can be shortened.

Scouting Tips

• Focus on lower branches and dense interior foliage first.
• Older infected needles often appear purple to brown before dropping.
• Black fruiting bodies may be visible with magnification emerging through stomata.
• Maintain coverage on expanding new growth during wet weather periods.

Elongated Hemlock Scale 

Elongate hemlock scale activity continues to increase slowly in Fraser fir plantings. While viable eggs were limited in some scouting locations this week, crawler emergence has begun at low levels, with several crawlers already observed in Fraser fir blocks. This could mean within  3 weeks away from elongate hemlock scale crawlers.

Crawler emergence is the most important management timing for this pest because crawlers are the most vulnerable stage to insecticide applications.

Scouting Tips

• Start searching in the yellowest or most off-color trees first.
• Focus on the bottom third of the tree and inspect older interior needles deep within the canopy.
• Look for pale spotting or mottled yellowing (chlorosis) on needles.
• Clip suspect twigs and examine indoors under controlled lighting.
• Using at least a 10x hand lens, inspect needle undersides for elongated, waxy brown female scales approximately 2 mm long.
• Compare findings carefully to known EHS photos if uncertain.

Weekly monitoring beginning now is highly encouraged. Growers should begin treatments when yellow mobile crawlers are consistently observed.

Because elongate hemlock scale produces multiple overlapping generations, continued scouting throughout the season is important. Follow pesticide labels carefully regarding retreatment intervals and seasonal use limitations. When possible, consider products with reduced impact on beneficial insects to help maintain long term biological suppression.

Erie County received over 5 inches of rain in April, and the wet weather has continued through the first days of May. Hemlock woolly adelgid and elongate hemlock scale were observed in Erie County landscapes, often on the same hemlock trees. Elongate hemlock scale was also found on Abies spp., The eggs of the elongate hemlock have not hatched yet, but with our warmer-than-normal temperatures, egg hatch monitoring should start now.

Mites

Spider mite eggs remain abundant in many locations, especially in blocks with carryover pressure from last season. Activity has been most noticeable during warmer days, while cooler temperatures have slowed development somewhat. As temperatures increase and humidity fluctuates, populations may increase rapidly.

Many growers are finding good success with miticides such as Envidor 2SC and Avid 0.15EC, particularly when applications are timed to active populations and good coverage is achieved deep into the canopy. These products work differently and target different life stages, making rotation and resistance management important as the season progresses.

Growers should also use caution with broad spectrum pyrethroid insecticides during periods of mite activity. While pyrethroids may help control certain insect pests, they can unintentionally flare spider mite populations by eliminating beneficial predatory insects that naturally help suppress mites. In some cases, blocks treated repeatedly with pyrethroids may experience rapid mite population explosions several weeks later, especially during warm, dry weather.

Fertilization practices should also be considered carefully in blocks with high mite pressure. Excessive nitrogen fertility can stimulate lush, tender growth that may favor increased mite reproduction and feeding activity. Trees already under stress from heavy mite feeding may struggle to utilize aggressive fertility programs efficiently. Maintaining balanced fertility while reducing tree stress can help improve overall tolerance and recovery.

Scouting Tips

• Use a hand lens to examine older interior needles first.
• Look for tiny moving mites and translucent eggs near needle bases.
• Tap branches over white paper to detect active mites.
• Continue monitoring populations weekly as warm weather returns.

Looking ahead

The coming week's pattern of mild temperatures, scattered showers, and periodic warmups is expected to continue driving gradual pest development and prolonged disease pressure. Rainfall and humidity will favor continued needle cast infection periods, while warmer afternoons will increase crawler movement and mite activity.

The combination of advanced crop development and highly variable spring weather continues to reinforce one key message for growers this season: Scout the field, not the calendar! Blocks can vary dramatically by elevation, exposure, species, and regional temperatures. Frequent monitoring remains the best tool for proper timing of both fungicide and insecticide applications.

The Next Report

The next scouting report will be available on May 14, 2026. Reminder, please submit observations anytime prior to Tuesday, May 12, 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.