Gymnosporangium juniperi-virginianae Schwein
Host: Eastern red cedar.
Alternate Host: Apple and crabapple trees.
Importance: This rust kills branch tips and causes unsightly galls (globe-like swellings) to form. When numerous, galls may slow growth and kill seedlings.
Look For: Brown warty galls, ½ to 2 inches in diameter, on twigs of red cedar.
MAY TO JUNE
Yellow-orange jelly-like fingers growing from galls, especially during rainy weather.
JULY TO SEPTEMBER
Orange leaf spots on nearby apple trees.
Biology: After warm spring rains, cedar-apple rust spores are produced in the yellow-orange fingers that erupt from round, woody galls on red cedar twigs. These spores spread to nearby apple trees where they cause orange spots on leaves and fruits. In summer and early fall, another type of spore produced on the apple trees infects nearby red cedar and causes new galls to form.
Monitoring and Control: In spring, look for galls on red cedar of all ages. If galls are too numerous to hand clip and are killing seedlings or making older trees unsalable, consider treating galls with fungicides.
Clip off galls on red cedar.
If practical, remove nearby apple trees to reduce infection on red cedar.
Apply a registered fungicide to the orange jelly-like galls once during the spring, and/or spray red cedar foliage three times, once every 2 weeks, beginning in midsummer.
Avoid planting red cedar near apple and crabapple trees.
Host: Eastern red cedar
|Cooley Spruce Gall Adelgid
Adelges cooleyi (Gillette)
Hosts: Colorado blue and occasionally other spruce species; Douglas-fir.
Importance: The nymphs of this species cause long curved persistent galls to form on the new shoot tips of blue spruce. These attacks may kill shoots, deform the tree, and lower its value as a Christmas tree. On Douglas-fir, nymph feeding discolors and distorts needles, but does not produce galls.
Look For (on spruce):
Galls: cone-like, green, purple, or brown swellings, 2 to 2 ½ inch long, on the tips of new shoots.
Look For (on Douglas-fir):
Yellow spots on bent or curled needles, caused by nymph feeding.
Small cottony balls dotting the undersides of needles.
Biology: On spruce, young females lay eggs in the spring under a mass of white, cottony wax near the terminal (end) bud. Nymphs hatch and feed at the needle bases of expanding buds, producing galls that enclose and protect them. After galls dry up in midsummer, the exposed nymphs will either continue their life cycles on blue spruce or fly to Douglas-fir to lay eggs. Feeding on Douglas-fir does not cause galls to form. The nymphs overwinter, and the next spring the winged forms may fly back to spruce, where they reproduce gall-forming adelgids and thus complete the life cycle. These adelgids can complete their life cycle on 1 or 2 hosts; however, injury tends to be more serious when they move between two hosts.
Monitoring and Control:
On blue spruce: Look for brown galls on trees of all ages in August. If galls are few and scattered, remove by hand. If galls are too numerous to hand clip, treat entire plantation this fall or the next spring.
Clip off and destroy green scattered galls before they turn red and open in July.
Cut and chip or burn heavily affected trees.
If needed, spray trees with a registered insecticide just before spruce buds break in late April or early May.
Or, apply a dormant oil in early spring or late fall when trees are dormant.
On Douglas-fir: Monitor trees of all ages throughout the growing season. If you find small cottony balls on the undersides of needles, treat entire plantation.
To control overwintering aphids, apply a registered insecticide to trees in early October or just before Douglas-fir buds break in April or early May. Spray trees when the temperature is above 60° F.
An application in late June to mid July may be needed to control later stages.
Or, apply dormant oil in early spring or late fall when the trees are dormant.
Keep Colorado blue spruce and Douglas-fir apart to limit the problem.
Hosts: Colorado blue and occasionally other spruce species; Douglas-fir
|Eastern Spruce Gall Adelgid
Adelges abietis (L.)
Hosts: Norway, red, white, Black Hills, and black spruce.
Importance: The nymphs of this species cause swellings or galls to form at the base of young shoots. The galled shoots become brown, stunted, and deformed, making the tree unfit for sale. A single tree may have hundreds of galls and can be repeatedly attacked.
Pineapple-shaped green or brown galls, ¾ to 1 inch long, at the bases of new shoots.
Biology: Females overwinter near end buds and lay eggs at bud bases in spring when buds begin to break. Nymphs hatch and feed in clusters on new needles, which collectively swell into the characteristic gall. The gall opens between mid August and October, allowing the adults to emerge, disperse, and reproduce.
Monitoring and Control: Look for brown galls on trees of all ages in mid to late summer. If galls are too numerous to hand clip, treat infested trees this fall or the next spring.
Clip off and destroy green galls before they turn red and open in late July.
Cut and destroy severely injured trees.
Spray infested trees with a registered insecticide in early April just before the buds begin to swell, or mid to late September after galls have opened.
Keep trees vigorous to avoid infestation.
Consider planting alternative tree species.
Hosts: Norway, red, white, Black Hills, and black spruce
|Eastern Gall Rust
Cronartium quercuum (Berk.) Miyabe ex. Shirai
Western Gall Rust
Endocronartium harknessii (J.P. Moore) Y. Hiratsuka
Hosts: Scotch pine.
Eastern Gall Rust: oak.
Western Gall Rust: none.
Importance: Rust infections on stems slow growth and gradually kill older trees. Young seedlings are girdled and killed quickly. Rust infections on branches kill individual branches, but not trees.
Galls: globe-like or spindle-shaped swellings on trunk or branches.
Red needles on recently killed branches.
APRIL TO JUNE
Cream-colored blisters filled with orange spores, located on the surface of galls.
Biology: Windborne spores of pine (western) gall rust spread directly from pine to pine. Eastern gall rust completes part of its life cycle on oak.
Monitoring and Control: Randomly select at least 50 trees scattered throughout the plantation and look for branch and stem galls at anytime during the year. If trees up to 7 years old average more than three galls per tree, consider treating entire plantation. Treat alternate hosts found within ¼ mile of plantation. If no alternate hosts are present, prune galls to prevent the spread of pine-pine gall rust.
Destroy and remove alternate hosts from plantations so that rust fungi cannot complete their life cycle.
Control pine-pine gall rust by removing galls from trees before they produce spores that can infect other pines.
Control rusts in nurseries by applying a registered, preventive fungicide. Have a pest specialist identify the rust and prescribe the best treatment and timing for your area.
Before planting, inspect stock for swelling caused by rust infection.
Replant failed plantations with a nonhost species.
Host: Scotch pine
|Northern Pitch Twig Moth (=Pitch Nodule
Petrova albicapitana (Busck)
Host: Scotch pine.
Importance: The caterpillars of this moth remove small amounts of bark in the crotches of young branches. This kills or deforms a few branch or stem tips, but seldom degrades Christmas trees. This pest usually occurs only within the range of jack pine, its preferred host.
A hollow, thin-walled, brownish pitch blister (nodule), about ½ to ¾ inch in diameter, in a branch crotch. Branch may be flagged (discolored and deformed) beyond the blister.
Small, reddish-brown caterpillars, ½ inch long, inside the blister.
Pests that cause similar symptoms: Flagged branches may be caused by eastern pine shoot borer, Sphaeropsis shoot blight, Pales weevil, pine root tip weevil, pine shoot beetle, or pine spittlebugs.
Biology: This insect needs about two seasons to complete a full life cycle. The young larva constructs a small blister-like nodule on a growing tip and overwinters there. The next spring, the larva moves to a twig notch and forms a larger nodulethe one normally seen on the tree. After pupating, the moth emerges, lays eggs, and the cycle is repeated.
Monitoring and Control: Begin looking for pitch blisters when trees reach shearing age. Treat by hand if common.
Break open pitch blisters and crush the larvae.
Clip off flagged, broken, or crooked branches and leaders while shearing, or simply wait for broken branch tips to fall off.