2026 Christmas Tree Scouting Report May 14, 2026

Weather Update 

Much of Pennsylvania experienced another variable week of spring weather, with periods of rain, cooler overnight temperatures, and moderate daytime warming continuing across many growing regions. While some southern and lower elevation areas continue progressing ahead of average, colder nighttime temperatures across much of the state have noticeably slowed overall tree development compared to the rapid advancement seen earlier this spring. Many growers are observing tighter bud progression, slower needle elongation, and delayed movement in certain insect populations following repeated nights dropping into the 40s and in some northern areas even cooler.

The slower overnight accumulation of heat units has helped reduce stress on newly emerging growth while slightly extending key management windows for several pests and diseases. Soil moisture remains generally favorable across most regions, although localized heavier rainfall events continue creating prolonged needle wetness periods favorable for fungal disease development. Growers should continue monitoring local growing degree day accumulations closely, as pest development remains highly variable depending on elevation, species, and regional temperatures.

The week ahead is expected to bring continued moderate temperatures with additional chances for scattered precipitation. While warm daytime highs may briefly accelerate growth, continued cool nights are expected to keep overall development somewhat slower and more manageable compared to previous warm springs. Continued field scouting remains critical as many pests are now entering important management windows.

Pest Information

Douglas Fir Needle Cast Diseases

Swiss needle cast and Rhabdocline needle cast remain major priorities across Douglas fir plantings as new growth continues elongating. Newly emerging needles remain highly susceptible to infection during this growth stage, particularly under extended periods of moisture and humidity. Many growers have completed initial fungicide applications and are maintaining protective coverage as shoots continue to expand. Some growers in the southeast are on their third, fourth or fifth sprays depending on their location, pest pressure, and length of elongation.

In areas where cooler nighttime temperatures have slowed elongation, protection windows may remain open slightly longer than expected. Continue monitoring new growth carefully and maintain spray intervals according to label recommendations and rainfall conditions. Interior lower branches continue showing symptoms from previous infections in some blocks, reinforcing the importance of protecting current season foliage.

Spruce Needle Cast Diseases

Rhizosphaera needle cast continue to be active concerns in spruce plantings, particularly in dense blocks with limited airflow and prolonged moisture retention. Cool nights combined with wet foliage periods continue favoring disease development. Growers should continue scouting interior canopies and lower branches for discoloration, premature needle cast, and black fungal fruiting structures.

Rhizophaera appears as neat lines of tiny black dots. The fungal spores enter through the stomata of the needles and germinate within 48 hours. First year needles are susceptible throughout the growing season, and a second infection period late summer is also possible. There is a long time period between infection and when symptoms appear making it difficult to diagnose. Around this time in May, you may start to see signs of infection from last year's infection. You will see fruiting bodies, and eventually those needles will yellow, turn reddish purple and needles will cast in the fall. Remove any severely infected branches. Fungicides should be applied when growth is 3/4- 1 1/4" long, or half elongation, and then again at full elongation around 3 weeks later. It may require two consistent years of spray applications to clear. Chlorothalonil products such as Bravo Weather Stik remain some of the most commonly used and effective protectant fungicides in Christmas tree production, with copper and mancozeb products also providing control where labeled. Fungicides protect only newly emerging needles and will not cure existing infections, making application timing critical. Thorough coverage throughout the canopy, especially lower interior branches where humidity remains highest, is essential for effective control. Cultural practices including improving airflow, maintaining spacing, and removing heavily infected trees also remain important parts of long term disease management.

Some growers of Canaan Fir have also reported similar symptoms. Samples have been sent to the Penn State Plant Diagnostic Lab for confirmation. 

Bagworms

Bagworms can become a serious issue in spruce, fir, arborvitae, and juniper blocks where populations may go unnoticed until feeding damage becomes severe. Successful management depends on understanding the pest life cycle and beginning scouting long before large bags become obvious later in the season.

Bagworms overwinter as eggs inside old female bags attached to branches from the previous year. Each bag may contain hundreds of eggs that hatch from late May through June, depending on temperatures and regional conditions. Newly emerged larvae are extremely small and often disperse by ballooning on silk threads, allowing infestations to spread rapidly through fields, windbreaks, and neighboring plantings.

Growers should now begin weekly scouting in historically infested blocks, older spruce plantings, arborvitae borders, windbreaks, and areas near buildings or hedgerows where infestations commonly establish first. Carefully inspect the lower interior branches for tiny caterpillars carrying small, spindle-shaped bags made of needles and silk. Early symptoms include clipped or browned needles, thinning foliage, and scattered defoliation.

Treatment timing is most effective when larvae remain small, generally from late June into early July across Pennsylvania. Products containing Bacillus thuringiensis provide excellent control of early instars while remaining softer on beneficial insects. As larvae mature, growers may transition to products containing spinosad, acephate, bifenthrin, cyfluthrin, lambda-cyhalothrin, or other labeled caterpillar materials depending on crop, larval size, and resistance management goals. Thorough coverage is essential because larvae become increasingly protected within their bags as they mature.

By late July into August, scouting should shift toward locating surviving larvae and monitoring adult male emergence. Pheromone traps should generally be deployed in early to mid-August before peak male flight begins. Traps can help identify active populations, map infestation hotspots, and predict areas requiring intensified scouting the following spring. Traps can be found through Great Lakes IPM. Winter sanitation through manual bag removal remains one of the most effective long-term management tools forn smaller or moderate infestations.

Spider Mites

Spider mite activity continues increasing statewide, with significant egg hatch and active populations reported in multiple regions. Cooler nighttime temperatures may slightly slow development rates, but growers continue reporting substantial carryover populations from last season, particularly in blocks that experienced flare-ups during late summer and fall.

Heavy egg populations and mixed life stages are now being found in dense interior foliage. Continued weekly scouting remains critical, especially in spruce and fir blocks with prior mite pressure. Growers continue reporting success using products such as Envidor and Avid for early-season management. Caution remains warranted when using pyrethroid materials, as disruption of beneficial predators may contribute to secondary mite outbreaks later in the season. Miticides labeled as ovicides target both eggs and active forms and often provide the longest control. Apply when the population is low or starting to build in numbers. Evaluate after 5 days for a second application 7-10 days later, in accordance to the label. Note that Envidor and other products are a one-time per season use. Resistance builds quickly in mites due to their fast reproduction so be sure to rotate products every third application.

Cryptomeria Scale

An important scouting observation this week involves cryptomeria scale on concolor fir. Unlike many conifers, concolor fir needles contain stomata on both the upper and lower needle surfaces. According to The Gymnosperm Database edited by Christopher J. Earle, concolor fir needles possess multiple stomatal rows on both sides of the needle, contributing to the species’ characteristic blue-gray appearance.

Field scouting confirmed live cryptomeria scale present on both upper and lower needle surfaces. This observation serves as an important reminder that thorough scouting and complete spray coverage are essential, particularly in dense interior foliage where populations may remain protected. Growers should inspect both sides of needles when evaluating infestations and treatment efficacy rather than assuming populations are confined primarily to undersides.

Overwintering scales have begun feeding. Males have an additional nonfeeding pupal stage before winged males emerge and fly to the females. Mating occurs and the male dies. Roughly 40 eggs are deposited by late May or early June. Crawlers emerge about 2 weeks after the eggs are deposited. This emergence can last for 6-7 weeks, but typically is at its peak 2-3 weeks after eggs are laid.  This typically occurs between 600-800 GDD. The crawlers crawl a short distance and begin feeding within a day of emerging. The crawlers start to build a waxy covering to protect themselves; this can form on top of dead females from multiple generations due to continual infections. This stage repeats itself in late July or early August. The second generation of crawler emergence typically occurs in mid-August, 1750-2130 GDD.

Growers should begin scouting and flagging heavily infested areas that require treatment. Reduction of high weeds should occur prior to spray applications to ensure full coverage. Place yellow sticky cards on the lower branches to trap the males; this will let you know egg-laying will soon follow. 

Elongated Hemlock Scale

In Late May, early June, or 360-700 GDD, eggs hatch. The crawlers move from under the female's covering to the underside of the needle. The piercing sucking mouth parts cause yellow spotting on the upper sides of the needle, and they begin to form their waxy protective coating. 6-8 weeks after emerging, females are present. Males molt and to the winged stage. Upon mating, the male dies and the female produces 12-16 eggs under the armored covering. 

Scouting tips: 

1. start searching at the yellowest tree
2. On the bottom third of the tree look for older needles (inside the canopy) that, from above, have pale spots on needles
3. Clip twigs with mottled yellowing needles, also known as chlorosis, off and take them indoors where you control the lighting
4. Using at least a 10x magnifier examine the undersides if needles looking for immobile elongated waxy brown coverings of females
5. Yellow Sticky traps can be used to trap the presence of winged males. 

These scales are most susceptible to insecticides when their young (crawlers) start moving away from the female scale.  If you check infested trees weekly starting now, I expect that you will start seeing the yellow crawlers (photo attached) in a month. When you see them, treatments should start. They have multiple staggard generations, so follow the pesticide labels that dictate how often reapplications can be made over the growing season. Some insecticides are less harmful to beneficial insects than other, and they say so on their labels. Consider them and next year only start treating when and where crawlers reappear.

We have had a few questions about comparing Safari to Dimethoate. We do not endorse one product over another, or over other product options,  just sharing the facts about each to facilitate grower decision making: 

Growers continue to ask about the differences between Safari and dimethoate for elongate hemlock scale control, especially in Fraser fir and true fir plantings where pressure has been increasing in recent seasons. Both products can be effective, but they fit very different roles in a management program.

Safari (dinotefuran) is a systemic insecticide that moves quickly through the plant and is ingested as scales feed on the needles. It tends to work best on crawler and immature stages and is often favored for long term management programs because it is easier on beneficial insects and predators compared to older broad-spectrum materials. Safari works well during periods of active plant growth when trees are moving sap efficiently, and many growers like it because it helps gradually clean up blocks over time with less disruption to overall tree health and beneficial populations. It is important to remember that dead scales may remain attached to needles for weeks after treatment, so effectiveness should be judged by reduced crawler activity and slowing populations rather than immediate disappearance of scales. Good coverage is critical for effective suppression. Dimethoate, on the other hand, is an older organophosphate chemistry that has historically been used as a strong rescue treatment for heavy infestations. It provides more aggressive knockdown activity and can suppress settled stages better than many products, making it useful when populations are already high and trees are showing visible decline. However, dimethoate is significantly harder on beneficial insects and predatory mites and carries greater applicator and phytotoxicity concerns, particularly during hot weather or on tender new growth. Because of this, many growers now reserve dimethoate for severe infestations or rotational use rather than relying on it as a season long program tool. Multiple applications may be needed in high pressure blocks with overlapping generations.

The biggest factor with either product, and other chemical options, remains timing. Elongate hemlock scale is most vulnerable during crawler emergence before the protective wax covering forms. Scouting for crawler activity with tape monitoring, hand lens inspections, or close needle observation is critical for successful control. In Pennsylvania, crawler activity commonly begins in late spring and can continue into summer with overlapping generations in heavily infested blocks.

For many operations, the best approach is not choosing a single product but understanding where each fits best. Safari is often preferred for cleaner long-term management and IPM-friendly programs, while dimethoate remains a strong option for aggressive suppression when populations are already severe.

Looking ahead

Over the next two weeks, growers should continue focusing on maintaining fungicide protection during needle elongation, monitoring spider mite development, scouting for emerging bagworm larvae, and thoroughly evaluating cryptomeria scale populations. Continued cooler nighttime temperatures may slightly extend management windows for several pests, but rapid advancement can still occur quickly following stretches of warm weather and rainfall. Consistent weekly scouting remains the most important tool for successful early season management.

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 all pesticide applications must remain in accordance with both federal and state regulations.

The next report

The next scouting report will be available on May 21, 2026. Reminder, please submit observations anytime prior to Tuesday, May 19, 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.