Spruce problem diagnosis for yard trees by Jana and Mike Albers, MNDNR Division of Forestry
Current or older needles eaten (1) Yellow-headed spruce sawfly Defoliation of leader and upper crown of trees less than 15 feet tall Usually occurs in clusters of young trees exposed to sunlight Larvae seen in late May through June No webbing or insect remnants Severe defoliation can lead to top-kill and even death of small trees Management: Apply chemical insecticide (not Bt) directly on larvae in early June, or when less than ½-inch long
Spruce budworm Defoliation of leader and upper crown in trees or all sizes Usually on trees exposed to sunlight and seedlings below infested mature trees Larvae present in late may through June Messy feeder, lots of debris, clipped needles, insect remains Empty pupal cases often present year-round Current or older needles eaten (2) Kills trees after several years of heavy defoliation Management: When larvae are small, spray foliage twice with Bt at one-week intervals
Current or older needles are discolored (1) Spruce needle rust Buds are green and alive Current-year needles are discolored Fruiting bodies on infected needles Disease causes needles to drop during the next year If infection is heavy, entire tree can look tan to pink in July and August Labrador tea is alternate host Disease is unpredictable, because presence and severity depend on cool, wet spring weather for needle infection
Current or older needles are discolored (2) Spruce spider mite Associated with dry weather; appears as though needles and twigs have dried Can see egg cases and mites with hand lens Frequently see very fine webbing along the twig; debris gets trapped in webbing and twig looks dirty If infestation is current, hold a piece of white paper below twig and tap to shake mites onto paper; mites and the tiny specks that move Management: Use a dormant oil in late fall or apply miticide in early June or twice in July Adult
Only older needles affected (1) Rhizosphaera needle cast Buds are green and alive Current-year needles are green Some or most older, infected needles turn brown to purple and fall off Black fruiting bodies found in needle openings, normally white (need a hand lens to see) Tree may have sparse-looking interior Management: Increase air circulation by pruning off lower branches and mowing under tree May apply fungicide when needles are half-elongated and again when fully elongated; treatment will be necessary for two or more years Healthy needle openings at top of photo below; fruiting bodies in openings of infected needles at bottom
Only older needles affected (2) Common needle casts (Lirula, Isthmiella and Lophodermium Buds are green and alive Current-year needles are green Some older infected needles become tan and fall off prematurely Black fruiting bodies are found on underside of needle on twoyear-old needles (photo below) Tree may have a sparselooking interior Management: May apply a single application of fungicide by July 1 Shape of fruiting bodies helps diagnose needle cast: Linear : Lirula (photo below) Short : Isthmiella Football-shaped : Lophodermium
No needles, twigs and branches dead Cytospora canker Especially a problem on Colorado blue spruce (photo, top right) Buds dead, no needles on infected twigs Infected twigs and branches can occur anywhere on the tree Lots of pitchy sap found at branch unions or cankers (below) Sometimes find golden spore tendrils coming out of dead twig or cankers (right) Management: Minimize stress by watering, mulching and fertilizing; avoid crowding and wounding branches and trunk Prune infected branches only during dry weather in late fall; sterilize cutting tool between each cut, otherwise disease is spread between trees
Weather-related damage to shoots or needles Late spring frost Associated with hard frost or low areas Several shoots droop over, wilt and may die Management: Chose hardier stock or stock with delayed bud-break Winter injury Due to loss of moisture during winter Needles turn brown from tip towards base Branches and twigs below snow are unaffected Management: Avoid planting on sites exposed to winter winds and late-winter heating; mulch and water well during growing season Heat can be reflected off buildings, so wrap exposed spruce in burlap or provide a screen between tree and building to protect them during winter
Leader wilted or dead (may include more than one whorl) White pine weevil on spruce Terminal leader with up to 3 whorls of branches drooped over and dead (photo, below left) All other branches unaffected Spruce of any age can be affected, but not serious once the trees are over 20 feet tall Larvae (below, right) are found under the bark at junction of live and dead tissues in stem during May, June, and into July; chip cocoons (far right) are evidence of infestation; may be 2-3 whorls down from terminal Insect prefers open-grown trees; lots of sun on leader Management: Where possible, plant under a light overstory; carefully prune and destroy attacked leaders containing larvae at the junction of live and dead tissue by July 15 before adults emerge Insecticides usually not a good option
Shoots and twigs swollen, needles green or dead Spruce gall adelgids and midges Eastern spruce gall adelgid Spruce gall midge Usually just an aesthetic problem; normally few galls per tree. Adelgids (related to aphids) cause swollen galls that include needle bases Current or older twigs curled Current needles may be green, but on older shoots with galls, needles are dead and red Midges (small flies) cause galls on the twig that do not include needle bases Management: Generally no need for control. May apply dormant oil in the fall. Remove green galls by pruning and destroy, because insects will mature and emerge from clipped shoots.
Pitch tubes on trunk, tree dead or dying Spruce beetle Beetles attack trees more than 10 inches diameter Larvae feed in galleries in inner bark Create pitch tubes less than ½inch in diameter on bark surface anywhere on the tree. Older pitch tubes turn grey and blend in with bark. Adult exit holes 3/32-inch in diameter. Streaks or strings of pitch on trunk and branches Trees may die in 1 to 3 years Infestation usually starts with blowdown or other local mortality. Mostly near North Shore, but can be found through central and northern Minnesota. Management is complicated; call MNDNR for more info.
Pitch masses on trunk, little effect on tree health: Pitch mass borer Insect prefers pole-sized trees Larva is grub-like, beige with brown head; up to 1 inch long Adult is a clear-wing moth that resembles a yellow-jacket wasp Moth has a 2-3 year life cycle Pitch masses are up to 4 inches across; usually solid Does not kill trees, but pitchfilled tunnels in sapwood causes lumber degrade Management: In urban settings, open pitch mass and kill larva or pupa with knife.
Miscellaneous Snowshoe hare damage Last year s apical bud destroyed by grosbeak feeding Yellow-bellied sapsucker damage Chip cocoons and pupae of small spruce weevil on trunk Armillaria root disease mycelial fan