no. 2.948

Pinyon Pine Diseases and Insects

by W.R. Jacobi and W.S. Cranshaw 1 (9/09)

Quick Facts...

  • Pinyon pines are well-suited to many parts of Colorado.
  • These pines make good visual screens, windbreaks, and wildlife habitat.
  • Major diseases include black stain root disease, dwarf mistletoe, armillaria root disease, and pinyon decline.
  • Common insect pests are pinyon pitch mass borer, Ips beetles, pinyon tip moth, pinyon pitch nodule moth, pinyon needle scale, and pinyon spindlegall midge.
  • To ensure optimum health, avoid wounding trees, choose an appropriate site, water properly, and give trees adequate space.

Pinyon pines are hardy, drought-tolerant trees well-suited to many Colorado landscapes. Their dense growth habit provides good visual screening and wind protection, and they offer shelter and food for birds and other wildlife. Site selection and proper maintenance are important for tree health.

Major Diseases

Black Stain Root Disease (Leptographium wagneri)

This vascular disease causes extensive black staining of the sapwood in the root and lower stem before killing the sapwood. Bark beetles tend to follow as secondary pathogens and eventually cause the death of the tree. Spread occurs through root grafts and root contacts, and by insects that carry the spores (reproductive structures of the disease). Affected trees usually are in a group.

Dwarf Mistletoe (Arceuthobium divaricatum)

These are small, leafless, parasitic flowering plants that grow on branches and spread only to other pinyon pines. They kill slowly by robbing the tree of its nutrients and water. Reproduction occurs when sticky seeds explosively discharge from the plant and adhere to the branches and needles of their next host. The life cycle from germination to dissemination is six years. This relatively slow rate of spread allows time for appropriate action.

Armillaria Root Disease (Armillaria spp.)

Armillaria spreads along roots and by rhizomorphs (fungal-root-like structures). One tree or a group can be attacked. The fungus can subsist on dead, woody material for more than 35 years. Armillaria prefers to infect trees that are already stressed by environmental factors or other pathogens. It prefers moist sites, moderate temperatures and is rarely found on extremely hot, cold or dry sites.

Pinyon Decline

Trees stricken with pinyon pine decline die slowly over several years. Affected trees have distinct symptoms that separate this disease from other problems commonly seen on pinyons. This environmental-related disease is not related to bark beetles, black stain root disease or other common problems. Environmental stresses such as winter drought followed by a hot summer may trigger the decline.

Black stain root disease Dwarf mistletoe
Figure 1: Vertical staining from black stain root disease. Figure 2: Dwarf mistletoe broom and plants.
Armillaria Pinyon decline
Figure 3: White fungal fans of Armillaria spp. Figure 4: Erratic branch mortality of pinyon decline.

Table 1: Diseases of pinyon pines.
Signs and Symptoms Management Options
Black Stain Root Disease
  • Yellowing and browning of needles.
  • Old needles drop prematurely; crown appears thin.
  • Resin may be exuded along trunk.
  • Distress cone crop or abnormally small cones.
  • Bands of jet-black wood at root collar and roots. Color does not cross annual rings like stain fungi carried by Insects.
  • Plant junipers, spruce or true firs in areas with the fungus. Ponderosa pine and Douglas-fir are hosts of other forms of this fungus, so do not plant them.
  • Trenching between trees may stop root-to-root spread if the trees on the other side of the trench are disease free.
Dwarf Mistletoe
  • Swelling of the bark at the infection site.
  • Brooming of highly infected branches.
  • Yellow foliage, reduced foliage and death of branches of infected areas of the crown.
  • The parasite itself: Yellow to green or brownish-green, segmented shoots, 1/2 to 6 inches long and 1/8 inch in diameter, protrude from branches. They form one to two years after infection.
  • Remove highly infected trees.
  • Prune lower infected branches, leaving at least one-third of the live crown. The shoots die as soon as the branches are pruned, so branch disposal is not a concern. Monitor effectiveness for 2-3 years. Repeat pruning as necessary.
  • If space permits, cut or plant other species in 50-foot or wider buffer zones between infected and healthy trees.
  • Remove the pinyon pine and plant another species in its place. Chemical sprays such as Florel remove mistletoe shoots, reduce seed production and prevent infection of new trees. This does not kill the plant, so retreatment is necessary until infected trees are removed and new trees are planted.
Armillaria Root Disease
  • Thin crown and/or chlorotic needles
  • Distress cone crop.
  • Resin flow at tree base.
  • Yellow, stringy rot at tree base.
  • White mycelial fans just under bark on roots and tree base.
  • Rhizomorphs on roots: black, shoestring-like structures with a white, nonwoody core.
  • Honey-colored mushrooms at tree base.
  • Remove infected species and plant resistant species such as juniper.
  • Improving growing conditions.
Pinyon Decline
  • Red or yellow needles.
  • Dead branches may be on one side of the tree or scattered around the tree.
  • As some branches die, others may remain green and appear healthy.
  • Within a group of trees, some may die, some may show no symptoms, and others may have part of the crown die.
  • If no precipitation occurs, water trees growing on well-drained soils once a month from November to June.
  • Cut trees with more than 40 percent dead branches, remove them from the site. Dying trees and firewood may attract bark beetles and are a potential fire hazard.
  • Chip removed trees for mulch, cut them up for firewood (stored off-site) or bury them in a landfill. Never stack firewood or fresh-cut wood next to living trees
  • Other diseases and Insects may damage these trees and need management.

Major Insects

Pinyon "Pitch Mass" Borer (Dioryctria ponderosae)

The larvae of this insect are pale yellow or pink with a light brown head. Larvae live underneath a pitch mass. Adult moths are active and lay eggs in tree wounds from late June through August. The larvae undergo four molts before changing to the pupal stage. Pupation takes place in the chamber of pitch and silk produced by the larvae. Larval feeding over the summer causes most of the damage. The life cycle is complete in one, sometimes, two years.

Ips (Engraver) Beetles (Ips spp.)

Adults are 1/8 to 1/4 inch long and reddish-brown to black. They have a pronounced cavity on the rear end that is lined with three to six pairs of tooth-like spines. Larvae are small, legless grubs (1/4 inch) that are white to dirty gray with dark heads. Adults lay eggs along galleries. Once the larvae hatch, they feed just inside the bark and mine away from the pupal chamber. From egg to adult takes 21 to 40 days in summer and several months in winter. The beetles are dormant during the coldest months, but sometimes are seen to be flying in early November and late February. Two to three generations are produced in most years with increased number of generations during warmer years.

Pitch mass borer
Figure 5: Pitch mass borer damage.

Pinyon Tip Moth (PTM) (Dioryctria albovittella)
Pinyon Pitch Nodule Moth (PPNM) (Retinia arizonensis)

PTM: Adults are small grayish moths. Larvae are light golden brown with a dark brown head capsule up to 3/4 inches long. They overwinter in a small, silk cocoon on the bark. In mid- to late May, they feed by tunneling into the base of the unopened buds. They mine the pith of the terminal growth, causing more damage as they grow. Large larvae move on to new tissue, cones or shoots. Pupation occurs inside the terminals and cones. Adults lay eggs from late June through August. There is one generation per year.

PPNM: Adults are a rusty brown. The larvae are reddish-yellow caterpillars with a black head and dark area behind the head. They overwinter as partially grown larvae within pitch nodules. Feeding resumes in spring and pupation follows in late spring. Adult flights typically peak in late July and early August. Eggs are laid on needle sheaths and the newly hatched larvae feed on young needles, later tunneling into shoots. There is one generation per year.

Pinyon Needle Scale

(Matsucoccus acalyptus)
Ips galleries on pinyon
Figure 6: Ips galleries on pinyon.

Females overwinter on the needle as a legless nymph that resembles a small black bean. Development into the mobile adult form resumes in the spring. Mating occurs in early April. Eggs are laid in masses around the collar, branch crotches and underside of larger branches. The eggs are covered by a white, cottony wax. Newly hatched nymphs settle on the previous year’s needles. Second stage nymphs form in late summer and overwinter on the needles. There is one generation per year.

Pinyon Spindlegall Midge (Pinyonia edulicola)

Adults are tiny flies, about 1/16 inch long, with an orange abdomen. The larvae are small, legless orange maggots found within swellings that form at the base of needles. Six to 15 larvae occupy each gall, that form as a result of larval feeding. In preparation to pupate the larvae produce a silken, white covering within the gall a few weeks before adults emerge. Adults are present shortly after new growth is produced on pinyon and emergence is indicated by the pupal cases that extrude from the tips of the needles. Adults mate and lay eggs on terminal buds from mid-June until early July. The eggs hatch and the larvae migrate down to newly formed needles. There is one generation per year.

Pinyon tip moth Pinyon pitch nodule moth
Figure 7: Pinyon tip moth. Figure 8: Pinyon pitch nodule moth.
Pinyon needle scale Spindlegall midge
Figure 9: Pinyon needle scale. Figure 10: Spindlegall midge.
Table 2: Insects of pinyon pines.
Signs and Symptoms Management Options
Pinyon "pitch mass" borer
  • Large gouges in the cambium of the trunk and branches exude a creamy, pinkish pitch.
  • Branches are weakened and may be susceptible
  • Branches dieback.
  • "Worm" borers out with a flexible wire, if they haven't tunneled too far in.
  • Preventive trunk sprays when adults are active can reduce new attacks. Thorough coverage is important, especially around active infestation sites. Two to three treatments each season, repeated over at least two years, may be needed. Pyrethroids, such as permethrin and bifenthrin, should be effective as preventive sprays.
Ips (Engraver) Beetles
  • Yellowish or reddish-brown boring dust in bark crevices or around tree base.
  • Y- or H-shaped galleries just beneath the bark.
  • Pitch tubes at entry points are about 3 inches long and 3/4 inch wide.
  • Needles change from green, to yellow to reddish brown.
  • Promote tree vigor with proper watering.
  • Newly planted or stressed trees are highly susceptible. Preventive insecticides (permethrin, bifenthrin) may be useful on recently transplanted trees.
  • Avoid piling pinyon slash in near vicinity of healthy trees. Large numbers of Ips beetles may develop in recently cut wood.
Pinyon Tip Moth (PTM)
Pinyon Pitch Nodule Moth (PPNM)
  • Twig dieback due to terminal feeding (PTM, PPNM).
  • Holes in cones created by the feeding (PTM).
  • Large amounts of pitch around wound site (PTM).
  • Pitch nodules at wound site are round, smooth and light purple or red. (PPNM)
  • Disfigured form and weakened tree (PTM, PPNM).
  • Spray in midsummer when larvae are exposed on the plant and/or in May when larvae become active and begin to enter stems (PTM).
  • Apply preventive insecticides (e.g., permethrin, bifenthrin) in late July and early August when the larvae are exposed on the exterior of the twigs (PPNM).
Pinyon Needle Scale
  • Older needles are generally attacked. Needles turn yellow, die and drop. Tree develop a "tufted" appearance because only new needles remain.
  • Repeated attacks can kill young trees and weaken older trees. A weakened tree is more susceptible to bark beetle attacks.
  • The white, cottony wax on the eggs can be quite visible in heavily infested trees.
  • No currently available treatments have been identified. Drenching trunk sprays of insecticides used to control other scale insects (e.g.,dinotefuran, imidacloprid) may be effective when applied as a trunk spray in early spring when scales mass on trunks. The addition of an oil may improve control.




Pinyon Spindlegall Midge
  • Spindle-shaped galls about 1/2 inch long at the base of developing needles.
  • Discoloration (yellow or red) of the affected area.
  • Premature death of attacked needles.
  • Predatory and parasitic wasps keep populations low. Insecticidal controls are rarely warranted.
  • Insecticides are most effective during egg laying and early gall growth. Use the silk produced by the pupae to time emergence. Older needles are not affected. Treat only newly developing needles.
  • Spinosad and permethrin are effective at egg laying.

Proper Maintenance

Pinyon pines are a hardy species, but it is still important to minimize stress and wounding. They are drought-tolerant and do not grow well above 7,500 feet. To reduce stress, provide adequate space, avoid overwatering, and do not plant them in soils high in clay. Activities that can cause wounding are construction, planting, yard work and logging.

If you are building on a site with established pinyons, do not locate structures within two tree heights of the tree. This is the extent of the underground root system. Proper planting of new or transplanted pinyons can minimize problems in the short and long term. Use lawnmowers and weed trimmers carefully to avoid trunk damage. Log carefully to avoid basal scarring and accidental branch removal.

In general, closely planted and overcrowded pinyons are more susceptible to insects and diseases than trees with adequate light and space. Excessive moisture in irrigated landscapes promotes succulent growth and branch cracking. These conditions provide good entry, egg laying and feeding sites for some insect species. Pruning can also create infestation sites. Allow enough time for wounds to close before adult insects are active.

Related Fact Sheets

1W.R. Jacobi and W.S. Cranshaw, professors; bioagricultural sciences and pest management. 8/99. Reviewed 9/09.

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