Needle Discoloration Chapter Banner
 
Needle Discoloration Graphic  
Needle Discoloration
or Distortion


Scattered, single needles or clumps of needles may be spotted, banded, stippled, or totally discolored- yellow, red, brown, or black. You may find fruitbodies, swellings, or scales on injured needles. Some may be distorted. If needles are chewed off, see next section. If shoots, branches, or entire trees are discolored, see other injury categories.
Black dividing line
 


Pollution Injury Banner

Air Pollution Injury
Hosts: All conifers, especially eastern white pine.

Importance: Air pollution reduces growth, causes early needle loss, increases vulnerability to diseases and insects, and occasionally kills trees.

Look For:
Yellowing, stunting, and early shedding of old needles.
• Yellow, red, or brown tips on current year needles.
• Yellow flecks, stipples, or bands on needles.
• Injury on nearby broad-leaved plants,
e.g., dead tissue at leaf margins (fluorides), or between leaf veins (sulfur dioxide), or stippling (ozone). Aspen, birch, alfalfa, and sweetcorn are particularly sensitive to air pollution injury.

Factors that cause similar symptoms: Drought, herbicide injury.

Biology: Air pollutants produced by automobiles (ozone), industrial processes (fluorides), and coal- and oil-burning factories (sulfur dioxide), will injure a wide range of plant species in or near Christmas tree plantations. The amount of damage depends on the age of the needles, genetic make-up of the tree, pollutant concentration, weather, and how long the tree was exposed to the pollutant. New needles are most susceptible when elongating during early summer.

Monitoring and Control: Remove dead shoots and trees to prevent a buildup of other pests on this material.

NEXT CROP
Yellow and brown tips....


Above:
Yellow and brown tips on current-year needles.

Below:
Stippling on nearby leaves.
• Before choosing a new plantation site, check the surrounding area for industries that may produce damaging pollutants. Most damage occurs within 10 miles of these sources, however, ozone injury can also occur in remote areas.
• Plant seedlings that are genetically resistant to air pollution injury. For example, spruces are resistant to sulfur dioxide, ozone, and fluorides; balsam fir, Fraser fir, Douglas-fir, and red pine are resistant to ozone.
Stippling on nearby leaves
Black dividing line
Hosts: All conifers, especially eastern white pine.


Balsam Fir Needle Rust Banner
Balsam Fir Needle Rust
Uredinopsis spp. and Milesina spp.

Host: Balsam and white fir; potentially Fraser fir.

Alternate Host: Ferns

Importance: Current-year needles that are infected turn reddish-brown, shrivel, and drop to the ground before the end of the summer. Infected trees will have sparse foliage. Several years of repeated infection can reduce tree quality.

Look For:
JULY TO AUGUST
Current year needles that are yellow with white pustules on the underside.

Biology: Current year’s needles of fir become infected as shoots are elongating. As the growing season progresses, infected needles turn yellow and produce spores in white pustules. These spores infect various species of fern (depending on the species of rust). The fungus overwinters on dead fern leaves and produces spores in the spring that are wind-disseminated back to the fir. Infection of fir trees requires cool, moist conditions during shoot elongation. If weather conditions are too dry, infection will not occur.

Monitoring and Control: Examine your trees from July through mid August. Be on the lookout for the rare occurrence of severely affected trees where more than 50 percent of the current year's foliage is infected and drops off. Consider management of the alternate host if you observe high disease incidence. This disease usually causes only a slight loss of current year's foliage. If disease incidence is low, management is probably not necessary. Infection is closely tied to specific weather conditions and will not occur every year.
• If disease incidence is high, mow or kill ferns in the plantation. Since spores are produced in the spring on dead fern leaves, expect lower levels of disease to begin one year after ferns are controlled.
Balsam needle rust
Black dividing line
Host: Balsam and white fir; poten


Balsam Gall Midge Banner
Balsam Gall Midge
Paradiplosis tumifex Gagne

Hosts: Balsam and Fraser fir

Importance: The larvae of this tiny fly feed on new needles, causing small galls to form on the needles. Galled needles drop prematurely, leaving bare spots on branches, which may lower the market value of affected trees. However, shearing can remove some affected branches and injured trees will recover satisfactorily if trees are not heavily infested again for 3 or 4 years.

Look For:
OCTOBER TO APRIL
Thin foliage and bare branches anywhere on the tree, particularly near the upper crown.
MAY
Adult female midges laying eggs on newly emerged shoots. Adults are orange in color and resemble mosquitoes in size and appearance.
JUNE TO OCTOBER
Galls: globe-like swellings near the base of new needles. In heavy infestations, there may be several galls per needle and more than 50 percent of new shoots may contain infested needles.
Small yellow or pink larvae inside galls. Each gall may contain one or two larvae; larvae of two midge species may be present in the same gall.

Biology: Mature larvae drop from the needles in the fall and overwinter in the mineral soil beneath the tree. Pupation occurs in spring and flying adults emerge from the soil in late May to early June. Females lay eggs on newly emerging foliage. Developing larvae feed on the needles, causing galls to form. Parasites attack newly laid eggs and also feed on the larvae inside galls. Predators prey upon cocooned larvae in the fall and spring. Adult midges and their parasites are vulnerable to insecticides between late May and early June when they emerge to mate and lay eggs.
Various midge damage shots
Black dividing line
Hosts: Balsam and Fraser fir
Monitoring:
ADULTS: Emergence traps can be placed beneath previously affected trees to estimate timing of adult emergence and egg laying. Traps can consist of either a bottomless small wooden box or opaque plastic flower pots placed tightly over the soil. The trap should have a small hole in the side which contains a clear glass or plastic vial exposed to the light. Adults that have emerged from the soil can easily be seen in the vial as they try to escape toward the light. Traps should be placed beneath previously infested trees in early May. Place one trap below each of 10 trees that are at least 10 feet apart.

GALLS: Look for galls anytime between June and October, starting 3 to 4 years before harvest. Infestations tend to be heaviest in the upper crowns of individual trees and in trees located near forest edges containing native balsam fir trees.

Control:
• Remove and burn heavily infested branches or trees in late summer before larvae and needles drop to the soil. Removing affected trees in early spring will only encourage emerging adults to lay eggs on nearby and perhaps previously uninfested trees.
• Kill adult midges by spraying heavily infested trees with a systemic or contact insecticide within 7 days of adult emergence from traps. If traps are unavailable, examine at least 3 lateral shoots of upper-midcrown branches from at least 10 trees frequently from late May to early June. Treat after budbreak but before needles are 1 inch long. Avoid spraying trees in areas where only a few midges are emerging or where only a few galls were present. This will conserve natural enemies that keep midge populations in check.
• Kill larval midges inside developing galls with a systemic insecticide. If applied before mid June, galls will stop forming and needle drop at harvest should be slight. Control is not practical after mid June because larvae are protected by fully formed galls.

NEXT CROP
• Avoid planting balsam fir or Fraser fir where midges have previously been a problem.
• Avoid planting firs in the outer rows of fields near forests containing native firs. Planting nonhost conifers or, if available, resistant fir varieties in these areas may reduce infestation levels.
Midgetrap
Black dividing line


Balsam Twig Aphid Title Banner
Balsam Twig Aphid
Mindarus abietinus Koch

Hosts: All species of fir, particularly balsam and Fraser; occasionally some spruce and pine species.

Importance: Balsam twig aphids feed on the sap of developing needles causing them to twist and distort in shape. Feeding causes aesthetic damage and stunting of new growth, which can reduce the value of Christmas trees for up to three years following attack. However, most of the needle curling straightens out once needles mature, and, if not, can be removed by shearing.

Look For:
JULY TO MARCH
Slight curling and stunting of previous years’ needles. Shoots may appear twisted and silvery.
APRIL TO EARLY MAY
Eggs or newly hatched nymphs on outer twigs, needles, and maturing buds. Eggs are less than 1/16 inch in size, black, and covered with fine white hairs. They are difficult to see without magnification. Newly hatched nymphs are yellow and often rest on the underside of the previous years’ needles within 2 inches of buds.
MAY
As budbreak begins, nymphs mature and produce offspring rapidly. The aphids form noticeable colonies on the expanding needles and their feeding causes distinctive curling of needles. Small amounts of woolly wax and honeydew are visible around groups of aphids. Insecticide treatment (unless systemic) from this time onward will likely do little to prevent damage; aphids are well protected within the shoots.
MAY TO JUNE
As infested shoots expand to 1 to 2 inches in length, green winged and wingless aphids covered with powdery wax and honeydew are noticeable. Current-year needles are often curled and bees and ants may feed on the honeydew. Ladybird beetles, green lacewings, and flower flies can be seen feeding on the aphids. Insecticide treatment (systemic or contact) at this time is too late to prevent current needle damage and kills natural enemies that help keep other pests in check.

Biology: Overwintering eggs hatch in spring (late April to early May) and nymphs quickly mature into stages that feed on developing needles. Several overlapping generations produce winged and wingless aphids by mid to late June. Heavy rainfall at this time may cause some aphid mortality. Numerous aphid-eating predators such as ladybird beetles, syrphid fly larvae, and lacewing larvae, feed on the aphids. By early July, the nonfeeding adults have mated and laid eggs on stems and bases of needles of new growth. Applying nitrogen fertilizer when trees are young or before budbreak in previously infested areas tends to increase aphid numbers. Densely planted trees and trees lower in elevation on slopes also tend to have greater numbers of aphids.

Monitoring and Control:
BEFORE BUDBREAK: The first generation of aphids does little feeding. These aphids and their cast skins can be found on the stem and older needles within 1 to 2 inches of developing buds. This stage is the most susceptible to insecticide control and treatment at this time may prevent further generations from developing. Detect aphids by beating the outer 10 inches of midcrown foliage over a small black cloth. Black cloth held in an embroidery ring works well. Sample aphids on at least two sides of 15 or more trees that are similar in location, age, and stock. If most trees have more than 2 aphids, and trees were damaged the previous year, treatment may be needed.
Aphid Monitoring
Black dividing line
Hosts: All species of fir, particularly balsam and Fraser; occasionally some spruce and pine species.
INFESTED SHOOTS: Once aphids move onto new shoots and the second generation is produced, infestations are visible to the eye. Infested shoots may be covered with aphids, white, waxy wool, and honeydew. Infestation levels can be estimated by counting the number of infested shoots and uninfested shoots per 10-inch branch of outer midcrown foliage from 15 or more trees per area. If the average number of infested shoots is greater than 30 percent, infested trees may need to be treated.
• Spray infested trees with a registered systemic insecticide just before budbreak if the area has suffered annual infestations that have caused permanent needle curling.
• Spraying trees when the needles begin to curl will probably not prevent damage from occurring.
• Avoid spraying trees or surrounding vegetation with insecticides when helpful aphid predators, such as flower flies, lacewings, and lady bird beetles, are present.
• Do not ship previously infested trees or nursery stock because overwintering aphid eggs can hitchhike to new areas.

NEXT CROP
• In the Lake States, plant local balsam fir seed sources; East Coast seed sources may be more susceptible to aphids.
• Avoid planting trees in dense stands or in areas with poor air circulation.
Aphid feeding damage
Black dividing line


Brown Spot Needle Blight Title Banner
Brown Spot Needle Blight
Mycosphaerella dearnessii M.E. Barr

Host: Scotch pine.

Importance: The browning and early needle loss caused by this fungus makes injured pines unsalable as Christmas trees.

Look For:
Reddish-brown, resin-soaked spots with yellow margins, on the needles. Spotted needles turn yellow, then brown.
Black fruitbodies flush with the surface of dead dry needles. These fungal structures stick out from the needle when wet.
AUGUST TO OCTOBER
Brown needles, especially on the lower branches and on the moist, shaded north side of trees. Needles turn brown from the tip towards the base of the shoot.
MAY TO JULY
New shoot and needle growth on the tips of branches that hold dead brown needles. Most dead needles fall off, leaving only tufts of new, green growth on the branch tips.

Pests that cause similar symptoms: Lophodermium needlecast, pine needle scale, winter injury.

Biology: Prolonged wet periods, particularly during June and July, provide favorable conditions for infection. Old needles are more resistant to infection than young ones.

Monitoring and Control: Inspect trees of all ages at least once between August and October. Randomly select 50 or more trees scattered throughout the plantation. Look for needle spots and browning on current-year and older foliage on the lower branches. If 15 percent of these trees are injured, consider treating the entire plantation next spring. If the infection occurs in small pockets, treat only the infected and surrounding trees.
• Cut and immediately remove small pockets of up to five infected trees. Trees that are within 30 feet of infected trees should be treated with a registered preventive fungicide.
• Or, if needed, apply a registered, preventive fungicide to all trees when needles are about half grown. Repeat two or three times, once every 2 to 3 weeks, to protect new growth and old foliage.
• Do not leave live infected branches on stumps of harvested trees because they serve as disease reservoirs.
• Do not shear infected trees during wet weather because spores released at this time may be carried from tree to tree on workers' clothes or shearing tools. Sterilize tools after shearing affected plantations by dipping in denatured alcohol for 3 minutes.
• Shear healthy plantations first so pathogen spores will not be carried into them from affected plantations.

NEXT CROP
• Plant only disease-free stock. If you suspect infection, have seedlings examined by a pest specialist.
• Plan disease-resistant varieties of Scotch pine, such as the long-needled varieties from Central Europe (see Table 1).
• Plant more than one species or variety so that one disease will not damage the entire crop.
• Do not plant Scotch pine seedlings next to Scotch pine windbreaks. Cut and chip or burn these windbreaks the year before planting a new stand. Also remove the stumps or treat them with a registered insecticide to prevent Pales and northern pine weevil attack.
Brown Spot Needle Blight
Black dividing line
Host: Scotch Pine.


Cyclaneusma Needlecast Title Banner
Cyclaneusma Needlecast (= Naemacyclus Needlecast)
Cyclaneusma minus (Butin) DiCosmo, Peredo, and Minter

Host: Scotch pine.

Importance: The early yellowing and needle loss caused by this fungus weakens and degrades Christmas trees.

Look For:
SEPTEMBER
Light-green spots on 2- and 3-year old needles. Spots enlarge and lighten in color, and needles eventually turn yellow, then brown
Yellow needles with dark-brown horizontal bands.
OCTOBER TO MAY
Shedding of yellow needles anywhere on the tree.
Off-white, waxy fruitbodies on brown needles. Most noticeable in wet weather due to swelling.

Pests that cause similar symptoms: Fall needle drop, pine needle scale, winter injury.

Biology: Needles of all ages are susceptible to infection. Most trees are infected between mid April and late June, but infection is possible through December. Cyclaneusma spores spread most readily after rainfall.

Monitoring and Control: Inspect trees of all ages in late fall and early spring. Examine 50 or more trees randomly scattered throughout the plantation. If 20 percent of the trees show symptoms of Cyclaneusma on the 2-year-old needles, consider treating entire plantation in early spring.
• Apply a registered preventive fungicide three times, once every 2 to 3 weeks between mid April and late June, starting before Scotch pine buds open. This control is about 50 percent effective. Continue spray schedule into late fall for complete control. This treatment may be too expensive for some growers.

NEXT CROP
• Buy planting stock from a nursery that uses preventive treatments for all diseases.
• If available, plant stock from seeds of trees that show genetic resistance to Cyclaneusma. The Northern European seed sources appear to be more resistant than the Mediterranean sources.
• Avoid planting next to old Scotch pine windbreaks.
5 Pictures of Cyclaneusma Needlecast
Black dividing line
Host: Scotch Pine.


Dothistroma Needle Blight Title Banner
Dothistroma Needle Blight
Mycosphaerella pini Rostr.

Host: Austrian pine.

Importance: This fungus infects and kills needles of all ages. Severely affected trees can be killed or may become more susceptible to other diseases.

Look For:
FALL
Yellow to tan needle spots that enlarge to form distinct brown to reddish-brown bands.
Dead needle tips beyond the reddish-brown bands. Needle base remains green.
Black fruitbodies in dead spots or bands on needles.

Pests that cause similar symptoms: Pine needle scale, winter injury.

Biology: Spores spread by wind and rain can infect needles throughout the growing season. However, new needles are not susceptible until they have emerged from the needle sheaths. Fruitbodies appear in the fall, and spores are released the following spring and summer.

Monitoring and Control: Check trees of all ages in the fall. If you find needle spots on any of your trees, consider treating the entire plantation next year. Take other preventive measures immediately to avoid spreading the pathogen.
• Do not shear trees when they are wet because spores released at this time may be carried from tree to tree on shearing tools.
• Apply a registered fungicide once between mid June and mid July to protect all foliage. For complete control, consider spraying once in mid to late May and again in mid June to mid July.
• Do not ship infected seedlings or Christmas trees because this fungus hitchhikes to new areas this way.

NEXT CROP
• Plant only disease-free nursery stock.
• Avoid planting Austrian pine. This tree is also very susceptible to winter injury.
• If you plant Austrian pine, plant disease-resistant varieties. Trees from a Yugoslavian seed source have shown resistance to Dothistroma.
• Do not plant Austrian pine near windbreaks of Austrian pine.

Brown bands and brown needles
Black dividing line
Host: Austrian pine.


Drought Injury Title Banner
Drought Injury

Hosts: All trees.

Importance: Drought-stressed trees lose foliage, grow slowly, and become more susceptible to insect pests and diseases. This is especially true of younger trees. Severe drought may kill trees.

Look For:
Wilting, dying needle tips and discolored foliage on the top branches. Symptoms may not appear until a year or more after trees have been stressed by drought.
Wilting of the current year’s shoots.
Dead tree top, short needles, and sparse foliage. These indicate a general decline in vigor that becomes evident in the years following the drought.

Pests that cause similar symptoms: Air pollution, Armillaria root rot, Leucostoma canker, Sphaeropsis shoot blight and canker, eriophyid mites, herbicide injury, Rhizosphaera needlecast, Scleroderris canker.

Biology: Drought stress occurs when trees need more moisture than is available in the soil. This condition may be caused by one growing season of severe drought or several seasons of below-normal rainfall. Young trees are especially sensitive to drought because their root systems are less extensive than those of older trees.

Monitoring and Control: Inspect stressed trees of all ages for injury by invading pests during and after periods of drought. Follow control recommendations for each pest as needed.
• Control weeds and grasses in and around plantations to reduce competition for water during dry periods.
• If drought conditions persist, irrigate to replace soil moisture in the root zone.
• Remove and chip or burn all dead trees as soon as possible; they may encourage other pest problems.

NEXT CROP
• Avoid planting on very sandy, drought-prone sites.
• Do not plant shallow-rooted species, such as true firs and spruce, in areas of low rainfall or on drought-prone sites.
• Remove weeds before planting.
• Irrigate during dry periods. This is especially important for young trees.
• Monitor planting closely; poorly planted trees are very susceptible to drought injury.
Dead tree tops wilting, dying needle tips
Black dividing line
Hosts: All trees


Eriophyid Mites Title Banner
Eriophyid Mites
Setoptus spp.

Hosts: Scotch, Austrian, red, and eastern white pine.

Importance: Immature and adult eriophyid mites discolor and distort foliage on pines by feeding on the buds and needles. Severe attacks degrade Christmas trees.

Look For:
Blotchy, pale yellow, stippled needles. The shoots of infested trees may have an unusually large number of buds, and needles may be twisted or hooked.
APRIL TO OCTOBER
Tiny cream-colored mites between needles or inside needle sheaths. To verify, pull the needle cluster apart until the needle sheath splits; then closely examine the lower part of the needle with a hand lens.

Factors that cause similar symptoms: Drought, herbicide injury.

Biology: Several overlapping generations of eggs are laid on the needle sheaths, starting when the weather warms. Mites feed on the tree’s sap under the needle sheaths. High numbers of mites result in discolored needles affecting tree appearance. Mite populations can swell when their natural enemies are inadvertently killed by repeated use of insecticides to control other pests.

Monitoring and Control: Inspect trees of all ages throughout the growing season. Treat infested trees as soon as you notice needles discolored by mites.
• Drench infested trees with a registered miticide (do not use an insecticide) anytime between May and September to kill adults. Depending on what miticide product is used, a second drench 10 to 14 days later may be needed to kill newly hatched mites. Be sure to follow directions on the pesticide label. The best time to treat for eriophyid mites is mid May to mid June, before needles fully elongate.
• Do not ship infested trees because overwintering mites hitchhike to new areas this way.
• Limit the use of insecticides to avoid killing mite predators.
Eriophyid mites
Black dividing line
Hosts: Scotch, Austrian, red, and eastern white pine.


Fall Needle Drop Title Banner
Fall Needle Drop

Hosts: All Christmas tree species.

Importance: Fall yellowing of inner foliage is a natural occurrence and does not harm Christmas trees before or at time of harvest. It is especially noticeable on eastern white pine and some varieties of Scotch pine.Yellowing of old foliage

Look For:
SEPTEMBER TO NOVEMBER
Yellowing and browning of the oldest foliage anywhere on the tree.

Pests that cause similar symptoms: Cyclaneusma needlecast.

Biology: All conifers shed their oldest needles each year. These needles turn bright yellow or brown in September or October and drop off at or before the harvest period. A healthy pine should have at least 2 years of needles after the oldest needles drop. A healthy fir or spruce should still have 4 to 6 years of needles.

Monitoring and Control: Not necessary.
Black dividing line
Hosts: All Christmas tree species.


Herbicide Injury Title Banner
Herbicide Injury

Hosts: All conifers.

Importance: Herbicides that are improperly applied or that drift while being applied can kill and deform needles, shoots, and, occasionally, entire trees.

Look For:
Yellow, bleached, or brown needles, especially new needles on the side of tree exposed to the herbicide.
Abnormal growth; twisted needles, hooked, distorted, or swollen shoots.
Damage that often shows up as a pattern; such as along one side of a field, along individual rows or trees, or only on one side of trees.

Pests that cause similar symptoms: Air pollution, salt injury, drought, distorted needles from balsam twig aphid (true firs), Cooley’s spruce gall adelgid (Douglas-fir), or eriophyid mites.

Biology: There are many different types of herbicides with different modes of action. They can enter trees through needles or through the roots. Hormone-type herbicides cause abnormal, exaggerated growth. Others slow growth by inhibiting photosynthesis or other life processes. The type and degree of injury will depend upon the herbicide applied, the concentration reaching the tree, the time of year, and the condition of the tree. Some products are lethal if applied when the trees are actively growing, but do not cause injury if applied when trees are dormant, such as in the late summer or fall. Other herbicides can be safely applied even during the active growth period.

Monitoring and Control: Check for injury during the first few weeks after herbicide application. Maintain a record of when and where applications occurred, the material applied, application rates, and information on weather conditions that occurred before and following Hooked shoots caused by picloramapplications.
• Prune dead shoots.
• Remove and chip or burn trees that are killed or severely affected by herbicides so that insects and diseases cannot build up on them and spread to nearby healthy trees.

NEXT CROP
• Follow label directions carefully.
• Avoid applying herbicides directly to the foliage of trees.
• Reduce the chances of drift: do not apply on windy days and use the proper equipment.
• Avoid planting Christmas trees near areas where herbicides are regularly used, e.g., powerlines, roadsides, and agricultural fields.
• Limit herbicide use and the number of applications whenever possible.
Black dividing line
Hosts: All conifers.


Lirula Needlecast Title Banner
Lirula Needlecast
Lirula nervata (Darker) Darker;
Lirula mirabilis (Darker) Darker

Hosts: Balsam, Fraser, and white fir

Importance: Injury ranges from scattered brown needles to the loss of most 3- and 4-year-old needles. Over a period of years, repeated infection can reduce tree growth, cause bud and branch mortality on the lower portion of the tree, and kill seedlings. Medium to high levels of disease caused by this pathogen decreases the quality of Christmas trees and makes boughs unusable for wreath-making.

Look For:
JUNE TO JULY
Second-year needles that are pale-green with patches of darker green, slowly turning brown. Blister-like ridges develop on the upper surface of the brown needles. These ridges vary in color, shape, and location according to the specific species of fungus involved.
Third-year needles that are tan to brown with a dark line on the midrib of the lower surface or underside of the needle.
AUGUST TO SEPTEMBER
Third-year needles that are shades of brown or gray; needles may be cast, broken off, or remain attached for several years.

Pests that cause similar symptoms: Rhizosphaera needle blight.

Biology: Spores are released from infected needles during rainy periods in June, July, and August. These spores infect current-year’s needles. Newly infected fir needles remain symptomless until the following spring when they begin to discolor. Infected needles then become pale and patchy green in color and slowly turn brown. Spore-producing fruitbodies develop in the upper surface of these brown needles in late spring of the second year and mature during summer. They appear as pustules or as blister-like ridges. In late summer of the second year, another type of spore-producing structure (ascoma) begins to form on the midrib in the lower surface of the needle. By the summer of the third year, this structure looks like a dark line along the lower midrib. Infectious spores are released from this structure and the cycle begins again.

Most injury occurs on small trees growing in cool, moist locations or on larger trees that are growing close to one another. Symptoms may be observed one to three years following a wet growing season. Damage is most evident on the lower branches (within 4 or 5 feet of the ground), where humidity is high and temperatures are lower. Disease is most prevalent in low-lying areas, shaded areas, and areas where trees are crowded together. Areas where young balsam or Fraser fir are surrounded by tall fir trees can be an ideal environment for high levels of disease. Young firs near windbreaks and trees adjacent to densely forested areas are commonly infected.
Lirula damage

Monitoring and Control: Examine trees of all ages at any time of the year. Look for second- and third-year needles that are various shades of brown and gray; these needles should also have one black line on the midrib of their lower surface.
• If disease incidence is low and infected trees are confined to the highly susceptible areas described under “Biology,” cultural management should provide adequate disease control. If disease is widespread throughout a plantation, contact your local forest health specialist for the latest information regarding chemical control. There is currently no fungicide registered to control Lirula needlecast.
• Do not leave live, infected branches on stumps of harvested trees; they serve as disease reservoirs.
• Shear healthy trees first so spores will not be carried into them from infected trees.
• Do not shear infected foliage during wet weather because spores released at this time may be carried form tree to tree on shearing tools. Disinfect tools after shearing affected plantations by dipping them in alcohol for 3 minutes.
• Prune lower branches and control weeds around the base of trees to allow more air flow.

NEXT CROP
• Locate plantations in areas where there is good air drainage.
• Carefully examine fir trees for infected needles before planting. Do not plant infected nursery stock. Do not introduce these diseases into your plantation by transplanting infected native balsam or Fraser fir.
• Do not interplant balsam and white fir in areas of your plantation where the disease is present. This will perpetuate the disease in the stand.
• Provide adequate space between trees to increase air movement around lower branches.
• If needlecast is a repeated and economic problem in your plantation, grow a tree other than fir.
Damage by Lirula mirabilis
Black dividing line
Hosts: Balsam, Fraser and white fir


Lophodermium Needlecast Title Banner
Lophodermium Needlecast
Lophodermium seditiosum Minter, Staley, and Millar

Hosts: Scotch and red pine.

Importance: This fungus kills red pine seedlings and causes dramatic browning on Scotch pines of all ages. Severely affected trees, weakened by early needle loss, are unfit for sale as Christmas trees.

Look For:
MARCH TO APRIL
Brown spots with yellow margins on the needles. Eventually needles turn yellow, then brown.
MAY TO JUNE
Brown needles, especially at the bottom of the tree. When severely affected, the whole tree will turn brown.
JUNE TO JULY
Fresh shoot and needle growth on the tips of branches that hold dead brown needles. Most dead needles fall off in June, July, and August, leaving only tufts of new, green growth on the branch tips.
JULY TO OCTOBER
Black, football-shaped fruitbodies on dead needles. Lophodermium fruitbodies have a lengthwise slit down the middle and stick out from the needle when wet.

Pests that cause similar symptoms: Brown spot needle blight, pine needle scale, winter injury.
Lophedermium Needlecast
Biology:Wind spreads Lophodermium spores from diseased needles to healthy needles in moist weather from August through October. The fungus overwinters in pine needles. In the spring, it destroys the water-conducting system in needles, causing the foliage to turn brown.

Monitoring and Control: Examine trees of all ages in May or June. Look for needle spots and brown foliage on the lower branches of 50 or more trees scattered throughout the plantation. If 10 percent of the trees are injured, consider treating the entire plantation starting in late July.

• Irrigate seedlings in the morning so that they will have time to dry in the afternoon. This will avoid the prolonged periods of moisture that favor infection.
• Do not ship infected nursery stock or Christmas trees because Lophodermium hitchhikes to new areas this way.
• Do not leave live, infected branches on stumps of harvested trees; they serve as disease reservoirs.
• Apply a registered, preventive fungicide 3 or 4 times, once every 2 to 3 weeks during the major infection period from late July through October. Apply more frequently if wet weather persists.

NEXT CROP
• Plant only disease-free stock. If you suspect infection, have seedlings examined by a pest specialist.
• Do not plant seedlings next to windbreaks of the same species. Cut and burn same-species windbreaks the year before planting a new stand. Remove the stumps, or treat them with a registered insecticide to prevent pales and northern pine weevil attack.
• Plant disease-resistant varieties, e.g., long-needled Scotch pines (see Table 1).
New shoot growth
Black dividing line
Hosts: Scotch and red pine.


Pine Needle Rust Title Banner
Pine Needle Rust
Coleosporium asterum (Dietel) Syd. and P. Syd

Hosts: Red and Scotch pine.

Alternate Hosts: Goldenrod, aster.

Importance: Most common on young trees up to sapling size, needle rust slows growth and causes unsightly foliage. When combined with insects and other agents that attack current-year foliage, needle rust may seriously damage or kill seedlings.

Look For (on pine):
APRIL TO MAY
Frosty-orange droplets on needles at the onset of warm weather.
MAY TO JUNE
Orange blisters erupting from needles on lower branches.

Look For (on goldenrod or aster):
JULY TO AUGUST
Orange spores on the undersides of leaves.
AUGUST TO SEPTEMBER
Orange, cushiony bumps on the undersides of leaves.

Biology: This fungus needs both pine and a herbaceous host to complete its 1-year life cycle. Pine needle rust spores produced on pine do not infect pine. Windborne spores from pine needles infect goldenrod or aster, and only spores produced on these alternate hosts can infect pines. Needle rust overwinters in pine needles. The fungus is perennial, so it can survive 2 consecutive years of unfavorable weather.
Orange blisters erupting from needles
Monitoring and Control: Examine 3- to 6-year-old trees in May and June. Check the needles of at least 50 trees scattered throughout the plantation. If you find orange blisters and serious foliage loss on more than 25 percent of these trees, remove goldenrod and aster in and around the plantation before August.
• Mow goldenrod and aster before August to avoid using a herbicide. These plants are perennial and will need mowing each year until the trees are old enough for the rust to have little or no impact on tree quality.
• Or, kill goldenrod or asters concentrated within 1,000 feet of newly planted seedlings before August by applying a registered herbicide. Without its alternate host, the fungus will not be able to complete its life cycle or infect pines.

NEXT CROP
• If practical, remove tall grass, weeds, goldenrod, and aster in and around plantation before planting. Avoid planting on humid sites north or west of a stand of tall trees, and avoid steep, northern or western slopes.
Orange bumps on underside of leaves
Black dividing line
Hosts: Red and Scotch pine


Pine Needle Scale Title Banner
Pine Needle Scale
Chionaspis pinifoliae (Fitch)

Hosts: All pines and spruces; Douglas-fir, eastern red cedar.

Importance: This insect weakens trees by sucking sap from the needles. Severely infested trees may have sparse, discolored foliage, low vigor, and dead shoots, and cannot be sold as Christmas trees.
Look For:
White-flecked or brownish foliage.
Many white or light-yellow, oyster-shaped scales, about 1¼10 inch long, covering the needles. Large scale populations can cause trees to look grayish green.

Pests that cause similar symptoms: Most needlecast diseases, sawflies (eggs look like scales).

Biology: Small, reddish eggs overwinter on the needles beneath dead, female scales. The crawlers (nymphs) hatch in mid May, move to new hosts, and settle on the needles to feed and grow. The scales mature in early July and produce a second generation of crawlers by mid July. While growing, the scales secrete and cover themselves with a waxy coating that most pesticides cannot penetrate.

Monitoring and Control: Inspect trees of all ages, looking for white flecks on the needles before lilacs bloom in spring. Be sure to check needles on lower branches where many infestations begin. Delay control of slight infestations on young trees, especially if predators such as ladybugs or lacewings are abundant on trees. These predators may curb an infestation. Treat individual trees when you see 5 to 10 white flecks per shoot. Treat all infested trees before shipping.
• Cut, remove, and destroy severely infested trees.
• Spray infested trees thoroughly with a registered insecticide or horticultural oil in mid to late May, when lilacs are in full bloom, to control first-generation crawlers. Spray again if needed in late July or early August when the second generation of crawlers hatch.
• Or, apply dormant oil in late fall or early spring when trees are dormant. This treatment will do little harm to scale predators.
• You should be able to spot treat individual infested trees.

NEXT CROP
• Reduce spraying for other pests in new plantings whenever practical. Scales often reproduce rapidly after repeated spraying for other insects because the insecticides kill both the target pest and the natural enemies of the scales.
Pine needle scales
Black dividing line
Hosts: All pines and spruces; Douglas-fir, eastern red cedar.


Pine Thrips Title Banner
Pine Thrips
Gnophothrips spp.

Hosts: Scotch and Austrian pines.

Importance: When severe, pine thrips feeding can distort needles and weaken, stunt, or kill Christmas trees or seedlings. Severely injured nursery seedlings are unfit for outplanting and injured trees are unsuitable for Christmas tree sale.

Look For:
Discolored, crooked needles, particularly on the upper branches. Severely injured trees die and lose their needles.
Curled needles anywhere on the trees. Needles growing from the same sheath may differ in size.
Brownish wounds, 1¼8 to 1¼4 inch wide, on the needles.
LATE APRIL TO OCTOBER
Orange-yellow or black insects, up to 1¼16 inch long, on the buds or new needles. Use a hand lens to see them clearly.

Biology: The winged, black adult thrips lay their eggs in May. Several subsequent generations produce thousands of insects that feed on trees throughout the summer. Hot, dry weather favors their buildup.

Monitoring and Control: Inspect trees of all ages throughout the growing season. Examine 30 or more trees in late summer. If an average of 10 percent of the needles in the tops of the trees show damage, treat entire nursery or plantation next spring. Treated trees will usually outgrow the injury in 2 to 3 years.
• Irrigate nursery seedlings frequently during hot, dry weather. Water with overhead sprinkler system early in the morning to discourage thrips and to reduce the likelihood of needlecast disease.
• Do not ship infested nursery stock or infested trees because overwintering thrips hitchhike to new areas this way.
• Thoroughly spray trees with a registered insecticide once in late April or early May before eggs are laid to control adult thrips. If you delay treatment until later in the season, two or three applications may be needed for complete control.

NEXT CROP
• Do not bring infested transplant stock into fields.
Pine Thrips
Black dividing line
Hosts: Scotch and Austrian pines


Rhabdocline Needlecast Title Banner
Rhabdocline Needlecast
Rhabdocline pseudotsugae Syd.

Host: Douglas-fir, especially Rocky Mountain variety.

Importance: The browning and early needle loss caused by this fungus make Douglas-firs unsalable as Christmas trees.

Look For:
LATE FALL
Yellow spots on infected needles. Spots eventually enlarge and cause mottling.
EARLY SPRING
Yellowish-brown to reddish-brown needles.
EARLY SUMMER
Shedding of brown needles. Severely diseased trees will keep only their current needles.

Pests that cause similar symptoms: Pine needle scale, Swiss needlecast.

Biology: Fruitbodies that develop on the brown needles release spores during moist weather from May to July. Windborne spores infect only the young needles.

Monitoring and Control: Inspect 5- to 10-year-old trees in May. Examine the 2-year-old needles on 50 or more trees scattered throughout the plantation. If you find fruitbodies on 20 percent or more of these trees, consider treating entire plantation in early spring.
• Shear healthy trees first so fungal spores will not be carried on shearing tools from affected trees to healthy ones.
• If possible, remove severely affected trees early in the rotation to prevent disease buildup.
• Apply registered fungicides when buds burst; repeat every 7 to 10 days until the buds are fully open. Fungicides applied after buds are fully open will not be effective. Fungicide treatments used for Rhabdocline should also control Swiss needlecast caused by another fungus that infects Douglas-fir.
NEXT CROP
• Plant only disease-free nursery stock.
• Plant disease-resistant varieties of Douglas-fir. If you plant a Rocky Mountain variety, select seed sources that show resistance to Rhabdocline.
Shedding needles in early summer...
Black dividing line
Host: Douglas-fir, especially Rocky Mountain variety.


Rhizosphaera Needle Blight Title Banner
Rhizosphaera Needle Blight of Firs
Rhizosphaera pini (Corda) Maubl
Host: Balsam, Fraser, and other firs.
Importance: This fungus causes a blight of needles on stressed trees or trees growing in shaded, damp, and cool areas. It can infect any age foliage and causes needle droop, discoloration and death, reducing the quality and value of trees. Greatest damage is to needles on lower branches where it may result in branch death.

Look For:
Yellow to tan needles. Needles turn grayish-tan and die. Needles may also droop. Before new growth occurs in the spring, all needles on individual severely affected branches may be dead from the tip of the branch to the tree trunk.
Tiny black fruitbodies on the undersides of green, yellow, and grayish-tan needles that can be seen with a hand lens. The fruitbodies emerge from the needle stomata (tiny pore-like openings on the underside of needles), and often have a speck of white wax on top of them.

Pests that cause similar symptoms: Lirula needlecast.

Biology: Symptoms often appear after periods of rainy weather and cool temperatures, anytime during the growing season. Spore release and infections probably occur throughout the growing season whenever favorable environmental conditions develop. Needles of any age can be infected. The needle may discolor soon after infection before fruitbodies develop or fruitbodies can develop while the needle is still green. Many infected needles remain on the tree over winter and into the next summer.

Severe injury occurs on stressed trees or trees growing in shaded, damp, and cool areas. Damage is most evident on lower branches where conditions tend to be cooler and damper, but may occur anywhere on the tree.

Monitoring and Control: Examine trees and foliage of all ages throughout the year. Previous year’s damage is most evident early in the spring before new growth develops, but symptoms and damage can develop anytime during the growing season. Fungicide recommendations have not been developed. The best control is cultural management to avoid stress and conditions favorable to the fungus.
• Promote good air movement by controlling weeds and pruning off lower branches.
• Do not shear during wet weather because spores could be carried to healthy trees on shearing tools. Disinfect tools after shearing. Shear healthy trees first.
• If infection is localized, remove and burn infected branches and trees. This should reduce but may not eliminate future infections.
• Do not leave live branches on stumps of harvested trees, as these can serve as disease reservoirs.
NEXT CROP
• Plant trees with adequate space between them to provide good air movement.
• Do not grow fir in shady areas or where cool, moist air collects.
• Plant only healthy stock, and do not interplant fir seedlings in fields where older, diseased trees are present.
Rhizosphaera needle blight
Black dividing line
Host: Balsam, Fraser and other firs


Rhizosphaera Needlecast of Spruce Title Banner
Rhizosphaera Needlecast of Spruce
Rhizosphaera kalkhoffii Bubak

Host: Colorado blue spruce; occasionally white spruce.

Importance: This fungus causes needles to turn purplish-brown and fall prematurely, thereby reducing the vigor and market value of Christmas trees. Three or four years of early needle loss kills branches and, in severe cases, the entire tree.

Look For:
LATE FALL OR EARLY SPRING
Fuzzy, black fruitbodies sticking out of tiny, pore-like openings (stomata) on both green and yellow needles. Use a hand lens. The yellow needles later turn purplish brown.
JULY TO AUGUST
Purplish-brown, 1- and 2-year-old needles, most commonly on the lower branches. Most of these needles drop off by late fall.

Pests that cause similar symptoms: Drought, pine needle scale, spruce spider mite.

Biology: Some infected needles remain on the tree throughout winter. The next spring, spores from infected foliage are rain-splashed or manually spread via equipment to newly emerging needles. Although infection is possible from mid April to October, it usually occurs during wet weather after bud break.

Monitoring and Control: Inspect trees of all ages during May. Randomly select 20 or more trees scattered throughout the plantation and remove three lower branches from each. Examine the white rows of stomata on the 2-year-old needles with a hand lens. If half the branches have fruitbodies on more than 10 percent of their needles, consider treating the entire plantation in spring and summer.
• Do not leave live, infected branches on stumps of harvested trees; they serve as disease reservoirs.
• Do not shear infected foliage during wet weather because spores released at this time may be carried from tree to tree on shearing tools. Sterilize tools after shearing affected plantations by dipping in denatured alcohol for 3 minutes.
• Shear healthy trees first so fungus spores will not be carried into them from affected trees.
• Apply a registered preventive fungicide when new needles are half elongated and again when needles are fully elongated. Two years of treatment should permit most trees to develop full foliage; severely affected trees may take longer. If treated early, Rhizosphaera needlecast can be controlled in 1 year.
NEXT CROP
• Plant only disease-free stock.
Rhizosphaera Needlecast of Spruce
Black dividing line
Host: Colorado blue spruce; occasionally white spruce


Salt Injury Title Banner
Salt Injury

Hosts: Many conifers. White pine, red pine, and balsam fir are especially sensitive to salt. Scotch pine is moderately tolerant. Colorado blue spruce and Black Hills spruce are relatively tolerant of salt.

Importance: Salt injury causes early needle loss, thereby degrading or making Christmas trees unsalable. Severe injury can kill branches and small trees. Trees affected by salt are usually those growing next to major roads and intersections. Damaged trees are generally found only within one or two outer rows in a plantation, usually within 100 feet of roads.

Look For:
APRIL TO JUNE
Browning of needles on the side of trees facing the road. These needles generally drop and new buds usually develop normally.

Pests that cause similar symptoms: Winter injury on most conifers, Brown spot needle blight on Scotch pine, Dothistroma needlecast on Austrian pine, Lophodermium and Cyclaneusma needlecast on Scotch pine.

Biology: Damage originates from both salt spray (salt deposited through the air onto needles, buds, and twigs), and soil salt (salt deposited in the soil occupied by the roots). The browning is often concentrated on the side of the tree facing major roads. Trees growing where salt accumulates, such as small depressions that drain water from roads or ditches along roads, can also be damaged. The affected foliage falls off during the spring and early summer, thinning the crown. New growth will make the tree appear otherwise healthy. However, trees repeatedly affected by salt often become stunted and grow slowly. They may eventually be killed by prolonged exposure to salt. Weakened trees may be killed by insects or disease.

Monitoring and Control: Monitor plantations between April and June. Look along the edges of plantations that are adjacent to major roads. The amount of injury can vary greatly between years, depending upon the amount of salt used on roads during the winter.
• Harvest trees as soon as possible after an injury-free winter.
NEXT CROP
• Avoid planting susceptible species, such as white pine, red pine, and balsam fir, along major roads.
Salt Injury
Black dividing line
Hosts: Many conifers, especially white pine, red pine and balsam fir


Spruce Needle Rusts Title Banner
Spruce Needle RustSpruce Needle Rusts
Chrysomyxa spp.

Hosts: Black, white, and Colorado blue spruce; occasionally Norway spruce.

Alternate Hosts: Labrador tea; leather leaf.

Importance: During spruce needle rust epidemics, infected trees will lose 25 to 75 percent of their new needles, leaving them unfit for Christmas tree sale. Repeated infections will slow growth but will rarely kill trees.

Look For:
JULY TO AUGUST
Yellow current-year needles anywhere on tree.
Whitish blisters filled with yellow spores on the undersides of current year needles.
AUGUST TO SEPTEMBER
Shedding of infected needles.

Biology: The fungi that cause spruce needle rusts need an alternate host to complete their life cycles. During the summer, windborne spores released from fungal blisters on spruce infect swamp heath plants such as Labrador tea or leather leaf. The fungi overwinter on these alternate hosts and spores released from them reinfect spruce the following spring.

Control:
NEXT CROP
• Avoid planting spruce near swamps that contain Labrador tea and leather leaf.
• Plant resistant species of spruce, such as Norway or Black Hills. White spruce is moderately resistant, but black and Colorado blue spruce are extremely susceptible.
Black dividing line
Hosts: Black, white, and Colorado blue spruce; occasionally Norway spruce


Spruce Spider Mite Title Banner
Spruce Spider Mite
Oligonychus ununguis (Jacobi)

Hosts: All Christmas tree species.

Importance: Mites may discolor, degrade or kill nursery stock and Christmas trees of all ages. Injury is most common during prolonged dry periods, on droughty soils, and where overuse of pesticides has killed the natural enemies of the mites.

Look For:
Yellowish to rusty-brown shoots. Look closely to see yellow mottling on needles.
Fine webbing between the needles. This may require a hand lens.
Dark-green to brown mites, less than 1¼50 inch long, on needles or webbing. To see mites, shake an injured branch over a piece of white paper, and focus a hand lens on the tiny moving specks.

Pests that cause similar symptoms: Rhizosphaera needlecast.

Biology: Mite eggs overwinter on shoots. Nymphs hatching in May or June feed on tree sap and spin webs. Adults appear in June or early July; three or more generations follow at 21¼2- to 3-week intervals until the weather turns cold. Mites are windblown to new areas or carried on infested nursery stock.

Monitoring and Control: Examine trees of all ages throughout the growing season, beginning in June. Delay control if injury or webbing is barely noticeable or if rainfall/humidity is high. However, if injury occurs during dry weather or if trees are to be harvested that year, treat individual infested trees as soon as you notice symptoms.
• Spray infested trees with a registered miticide in early June to early July when you first see mite activity. Some miticide products should be applied only once a year, ideally in early summer. Other miticide products may need to be applied at 2–week intervals to kill mites emerging from eggs. Be sure to follow application directions on the label.
• Or, spray trees thoroughly with a dormant oil early next spring before growth starts.
• Do not ship infested nursery stock or Christmas trees because overwintering mites hitchhike to new areas this way

NEXT CROP
• Avoid planting on droughty soils, especially when planting spruce.
• Plant only pest-free nursery stock.
Spider Mite damage
Black dividing line
Hosts: All Christmas tree species


Swiss Needlecast Title Banner
Swiss Needlecast
Phaeocryptopus gäumanni (T. Rohde) Petr.

Host: Douglas-fir

Importance: The browning and early needle loss caused by this fungus results in trees that are unfit for sale as Christmas trees.

Look For:
SPRING AND FALL
Rows of fuzzy black fruitbodies in tiny, pore-like openings (stomata) on the undersides of both green and yellow needles. Use a hand lens to see them. Yellow needles later turn brown.
JULY TO AUGUST
Brown, 2- and 3-year-old needles, especially on the lower branches. These needles fall off in late August.

Pests that cause similar symptoms: Pine needle scale, Rhabdocline needlecast.

Biology: Airborne spores infect needles on new shoots during wet weather at the time of bud break. The fungus is commonly spread on infected nursery stock.

Monitoring and Control: Inspect 4- to 10-year-old trees during May. Randomly select 20 or more trees scattered throughout the plantation, and remove three sample branches from each. Examine the white rows of stomata on the 2-year-old needles with a hand lens. If half of the Swiss needlecastbranches have fruitbodies on more than 10 percent of these needles, consider treating the entire plantation before summer.
• Do not shear infected foliage during wet weather because spores released at this time may be carried from tree to tree on shearing tools. Sterilize tools after shearing affected plantations by dipping in denatured alcohol for 3 minutes.
• Shear healthy plantations first so fungus spores will not be carried into them from affected plantations.
• Apply a registered, preventive fungicide in spring when the new shoots are 1¼2 to 2 inches long. Apply again in 2 to 3 weeks, and once again if rainfall is abnormally high. Two years of treatment should restore most trees to full foliage; severely affected trees may take longer. Treat nursery stock every 2 weeks from bud break to mid August.
NEXT CROP
• Inspect planting stock carefully. Plant only disease-free stock.
Black dividing line
Host: Douglas-fir


Winter Injury Title Banner
Winter Injury

Hosts: Short-needled Scotch pine varieties; Austrian and white pine; Norway spruce; white fir; Fraser fir; occasionally other Christmas tree species.

Importance: Winter burn and winter drying cause needles to turn brown and fall off, thereby degrading or making Christmas trees unsalable. Severe injury for several years may kill branches and occasionally kill trees.

Look For:
Lack of foliage, especially on the south side of trees where injury is usually most severe.
APRIL TO JUNE
Browning of entire tree or brown needles above the winter snowline at the onset of warm weather. These needles drop and new buds usually develop normally.

Pests that cause similar symptoms: Brown spot needle blight on Scotch pine, Dothistroma needlecast on Austrian pine, Lophodermium and Cyclaneusma needlecast on Scotch pine, salt injury.

Biology: Water cannot move easily in soil and in trees in the winter, so when moisture is lost, it cannot always be replaced in sufficient amounts. When the soil around tree roots is frozen, warm winds can dry out and damage needle, bark, and bud tissues. Winter burn causes needles to turn brown during fast temperature changes, particularly on the south side of trees where exposure to the sun is greatest. Temperatures change quickly at sunset and sunrise or when sunlight is suddenly blocked by other trees, hills, or buildings. Sometimes winter burn and winter drying will occur together, occasionally complicated by drought. The amount of injury depends on climate and on how well the Christmas tree species or variety can withstand winter conditions. Exotic trees (those grown outside their native ranges) tend to be especially susceptible to winter injury.

Monitoring and Control: Select 50 or more trees of any age scattered throughout the plantation and look for browning between April and June. Keep accurate records of winter injury throughout the life of the trees. If more than 10 percent of them are periodically degraded by winter injury, avoid replanting the same species or variety on that site.
• Harvest old, susceptible trees as soon as possible after an injury-free winter.
• Figure the cost-benefit of keeping young, susceptible trees. If not profitable, destroy the trees and replant with resistant ones (see Table 1).
NEXT CROP
• Plant resistant species and varieties, such as the long-needled Scotch pine varieties; red pine; white, blue, and Black Hills spruce; Fraser fir; and balsam fir (see Table 1).
• Avoid planting susceptible species and varieties, such as Spanish Scotch pine, Austrian pine, or Norway spruce. If you do plant susceptible trees, plant them in areas that are protected from the wind or in southern areas where temperatures are not as extreme.
Winter Injury
Black dividing line
Hosts: Short-needled Scotch pine varieties; Austrian & white pine; Norway spruce; white fir; Fraser fir; others