IPM for Christmas Trees: Seasonal Monitoring Guide

A good scouting program for your Christmas tree farm can lead to a more accurate pest and disease control program.
IPM for Christmas Trees: Seasonal Monitoring Guide - Articles


Scouting. Courtesy of Cathy Thomas, PDA

A good scouting program for your Christmas tree farm can lead to a more accurate pest and disease control program. Set time aside to scout for new insect and disease problems several times a year. Also take time to intensively scout for known pests to best determine the need for and timing of controls. As a rule, every time you are in a block of trees for planting, spraying, shearing, mowing, or harvesting, make note of any insect or disease issues. Combine these scouting tips with the control recommendations in the corresponding pest fact sheets found in this manual.

Be prepared with the proper scouting tools before beginning these scouting activities. The first and most important tool is a hand lens of 15X magnification or higher. Other tools include pruners to clip branches for sampling, plastic bags or vials to collect samples, and a pencil or pen and paper to record your findings.

Disclaimer: The suggested timing of the following scouting recommendations are based on general pest activity times in the Mid-Atlantic region. The best way to adapt this calendar to your region of the country is to follow the growing degree day timings listed in the fact sheet section of this manual. Also, the specific tree varieties on your farm may require that your scouting activities include pests not listed in this section.

Time of year: Late winter to early spring (March to early April), before bud break

HostsPestHow to Scout
True firsBalsam twig aphid - Look for trees with curled last season’s needles.
- On undamaged shoot, look for silvery,
oval-shaped eggs on underside of twig within 1–2 inches of buds.
- Light green stem mothers feed on undersides of needles, excreting honeydew droplets.
Colorado blue spruceCooley spruce gall adelgid - Look for brown, pinecone-like galls from the previous season.
- Gray-black overwintering nymphs are found at the base of the new season’s buds.
Douglas-firCooley spruce gall adelgid - Look for crooked needles.
- Black nymphs will be on undersides of needles (may be covering over with white wax).
Norway spruceEastern spruce gall adelgid - Look for brown galls at the base of previous year’s growth; needles may be missing beyond gall.
- The black overwintering nymphs will be found at the base of the new season’s buds.
Pines, spruces, true firsEriophyid mites - Look at 20 trees per acre that exhibit a gray or rusty coloring.
- Tiny, peach-colored eggs are found in clusters or rows at the needle base (underside).
- Pale, oblong adult mites move along the needles.
PinesPales weevil - Look for trees showing “flagging,” or browning, of needles at the ends of branches that have shown signs of chewing on stem bark.
- Pull duff away from base of last year’s stumps to look for adult weevils that are becoming active.
Douglas-firRhabdocline needle cast - Scout trees in areas likely to hold extra moisture such as shaded areas along a woodlot or tight plantings.
- Examine current season’s needles for orange-rust discoloration.
SprucesRhizosphaera needle cast - On the lower half of the tree, look for purple-brown needles with visible black fruiting bodies.
SprucesSpruce needle rust - On cloudy days, look for needles with yellow bands containing an orange spot.
- Focus scouting in low or shaded areas.
Arborvitae, Douglas-fir, spruces, true firsSpruce spider mites - Look for discolored (brown or yellow) needles.
- Red eggs are found on the undersides of twigs, needles, and at base of buds.
- Reddish-brown adult mites move along needles and twigs.
- Tap symptomatic branches over a white surface to dislodge eggs or mites.
Douglas-firSwiss needle cast - In shady or tightly planted areas, look for trees with needles that are browning from the tip down.
- On the underside of these needles, rows of tiny, black fruiting bodies will be visible with a hand lens.
- Also look for fruiting bodies on healthy, green needles.
Douglas-fir, pines, sprucesWhite pine weevil - Set out baited pyramidal traps (see Appendix E for instructions).
- Check soil temperature daily on unshaded side of a tree in susceptible block.
- Once soil temperatures near 50°F, check traps daily.
- On sunny days, look for sap droplets on tree leaders as feeding evidence.

Time of year: Midspring to early summer (early April to June)

HostsPestHow to Scout
Arborvitae, Douglas-fir, pines, spruces, true firsBagworm - Look for trees with brown, conelike bags, 1–2 inches in length hanging from the previous season’s growth.
- Near the end of May, begin to look for tiny larvae feeding on the new season’s needles.
True firsBalsam woolly adelgid - Look at the tops of trees for crooked leaders.
- On symptomatic trees, try to bend the main trunk. Trees with balsam woolly adelgid will be extra stiff.
- Branches will have gouty enlargements, or “warts.”
- Small, purplish-black insects will be under the white, woolly wax on the bark.
Douglas-fir, spruces, true firsCryptomeria scale - Lift the lowest branches of select trees to look for yellow speckling on top of needles.
- Examine underside of needles for off-white, oval-shaped scales with yellow centers. Look closely with hand lens for moving, yellow, oblong crawlers among the scales.
- In August, monitor for the second generation.
Douglas-firDouglas-fir needle midge - Prior to bud break, set out cardboard emergence
traps (see Douglas-fir needle midge fact sheet) at the base of trees with kinked or damaged needles from the previous season.
- As buds swell, monitor traps for delicate, orange midges in the capture jar.
- Emerging midges will also be found on breaking buds or hovering close by.
Douglas-fir, hemlocks, spruces, true firsElongate hemlock scale - Look for yellowing needles with a gray cast at the base of the trees, near the trunk.
- Examine the underside of the needles for mobile, yellow, oblong crawlers among the narrow, brown scales and shorter, white scales.
- Tapping the branch over a white paper or clipboard may dislodge the crawlers.
- Monitor for continuing generations throughout summer.
Douglas-fir, pines, spruces, true firsPine needle scale - White, oblong scales can be found on the most recent year’s needles.
- Look underneath the white scales to see if the purplish-red eggs have begun to hatch.
- Paprika-colored crawlers will be visible on the needles.
- Look for second generation in July.

Time of year: Harvest (November to December)

HostsPestHow to Scout
True firsBalsam woolly adelgid - Observe cut stumps for indications of the red reactionary wood.
Douglas-fir, pines,
spruces, true firs
Cryptomeria scale - Observe underside of branches for presence of scale.
Douglas-fi r, hemlocks,
spruces, true firs
Elongate hemlock scale - Observe underside of branches for presence of scale.