Christmas Tree Scouting Report: May 22, 2025

Weekly scouting report compiled by Kelly Piccioni, Penn State Extension, Schuylkill County. This week's scouting data contributors: Kelly Piccioni, Penn State Extension, Don deMackiewicz, Sarah Pickel and Cathy Thomas (PDA), Jim Fogarty (Schuylkill County)

Pest Information

This past week brought moderate spring conditions across much of Pennsylvania. Daily highs ranged from the mid-60s to upper 70s, with nighttime lows in the low 50s. Southeastern and south-central regions received scattered rainfall, while many northern and higher elevation areas remained relatively dry. This variability in moisture levels is influencing both disease development and insect activity. Growing Degree Days (GDD): Southeastern counties are now exceeding 350 GDD, with central and northern areas progressing steadily. This uptick signals increased pest and disease pressure across a range of species.

Elongated Hemlock Scale 

Elongated Hemlock Scale eggs and crawlers have been found in York County.  Only eggs have been found in Berks and Schuylkill Counties. Unlike many scales, EHS has multiple overlapping generations and can be active nearly all season. Peak crawler activity typically occurs in late May (after 500-550 GDD) through June, with additional flushes in August to September. For scouting purposes, Don deMackiewicz shared that when tapping the branch, the wax coating resembled artificial snow. Sticky traps are a great tool to help monitor for crawlers.  Adult females are flat, oval, brown to gray covers aligned with the needles of the tree.  The males are smaller and whiter in appearance. The most susceptible stage for treatment is the crawlers appearing tiny, yellow, and mobile.

Cryptomeria Scale 

No eggs have been found yet in our scouting region. Cryptomeria scale is a sneaky, armored insect that hides on the underside of needles, making it hard to spot unless you're really looking. The adults look like tiny, oval, yellow-tan spots with a see-through center. Affected trees will start to show yellow speckling on the tops of older needles, and you might notice some early needle drop. If the problem gets bad, the whole tree can start to look dull or off-color from a distance. In Pennsylvania, the first wave of baby scales (called crawlers) usually shows up in May to June, once we hit around 500–550 growing degree days (GDD). The second round comes in late July through August. Since there are two generations per year, it's important to keep scouting all season—especially during warm, dry spells when these pests thrive. When scouting, pick trees at random throughout the field, especially those in shaded or stressed spots. Look under older needles using a small hand lens. If you press gently on the scale and it’s soft or juicy, it is still alive. You can also wrap double-sided tape around twigs to catch crawlers. They will appear as tiny, yellow dots. Monitor closely during peak crawler times. Scale tends to show up first in dense, shady parts of the field, near wooded edges, or where airflow is poor. Keep an extra eye on blocks that have had scale issues before or trees that went through drought stress- which impacts most growers in Pennsylvania.

Chemical Information:

Horticultural oil is a tried-and-true option for scale control, especially early in the season. It works by smothering eggs and newly hatched crawlers before they form their protective covering. It's most effective when applied during dormancy or right at crawler emergence. This is a softer choice on beneficial insects and fits well in IPM programs. Just be cautious with temperatures—hot weather or mixing with the wrong products can cause needle burn.

Pyriproxyfen (sold as Distance and similar products) is an insect growth regulator that stops young scale insects from maturing. It doesn't kill on contact, but is very effective when timed right during crawler activity. It's also gentle on predators and parasites, making it a solid choice for an IPM rotation. Just remember: timing is key—it won't touch adults or hardened scales.

Bifenthrin (like Talstar, Menace, or Fame) is a fast-acting pyrethroid that knocks down crawlers on contact. It's very effective for heavy populations but also hard on beneficial insects. It's best used when crawlers are actively moving, and only occasionally—avoid back-to-back sprays to prevent resistance and preserve natural enemies.

Dinotefuran (sold as Safari and others) is a systemic neonicotinoid that moves through the tree to reach feeding scales, even those hidden deep in the canopy. It's a great option when pressure is high or infestations are widespread. It's usually applied as a soil drench or trunk spray, so good timing and soil moisture are important for uptake and effectiveness.

Spirotetramat (known as Movento) is another systemic option that moves both up and down within the tree. It works best on young scale stages and offers long-term protection if applied early. It's not a quick fix but adds great residual control when included in a preventive program. Like all systemics, it needs time to be absorbed and won’t give immediate results.

Needle Cast

By this time, growers should have their third application of Chlorothalonil on their trees. Many growers are considering the fourth and fifth application as previously discussed. Through our farm visits, we are seeing higher than normal cases of Swiss Needle Cast.  To scout, check the lower third of the tree, and compare new growth to last year's growth. The damage will be visible on last season's needles. Check the undersides of the needles for the spores. For more information, check out Penn State Extension's factsheet on Douglas fir needlecasts.

Other Important Activity to Note: 

Oriental bittersweet (Celastrus orbiculatus) growing very quickly. For best control, combine cutting with herbicide treatments. Cut vines at the base and again at chest height to disrupt growth. Follow up with herbicide—glyphosate (e.g., Rodeo) at 3 quarts/acre or triclopyr amine (e.g., Garlon 3A) at 2 quarts/acre as a foliar spray from July through early fall when foliage is active. For basal bark treatments, apply 20% triclopyr ester (Garlon 4 Ultra) in basal oil directly to the lower 12–18 inches of the stem year-round. Cut-stump applications using concentrated glyphosate or triclopyr should be made immediately after cutting to prevent regrowth. Always avoid spraying desirable trees and follow all label safety precautions.

Poison Hemlock is in its flowering stage and can cause physical harm when touched. Toxic alkaloid levels are at their peak during flowering, making all parts of the plant, especially the roots and seeds. It is highly poisonous to humans and animals. Handling the plant can cause skin irritation, and mowing or cutting can release toxic particles into the air. It's also easily mistaken for look-alikes like Queen Anne's lace. Avoid mowing when in bloom, and if removal is necessary, wear full protective gear. Herbicides like glyphosate or triclopyr are most effective before flowering or shortly after cutting. Never burn poison hemlock, as toxins can become airborne.

Mite activity has slowed down, but important to continue monitoring. Sticky traps are an easy, inexpensive, yet effective scouting tool.  You will also see the damage done by the Balsam Twig Aphids by observing twisted new growth.  Treatment is no longer effective, but it is important to know where you have damage so treatment can be effective next season. As the weather stays cool and rainy to end this week, we do not anticipate much advanced activity. Once the temperatures rise and the sun is shining again, activity will ramp up quite quickly. Place sticky traps and monitoring tools to see what is active on your farm. 

We are still visiting farms and taking samples. We are doing our best to get to see everyone. Please email Kelly at keg200@psu.edu to schedule a visit. 

Have a great and safe Memorial Day weekend! The next scouting report will be available on May 29, 2025.