Pine Tree Diseases and How to Treat Them

Green Pine Needles

If you’re noticing brown needles on your pine tree, it’s likely not because winter is coming. Pines are evergreen trees, which means a healthy pine should stay green all year long. If your pine needles are discolored and falling off, this could be a sign of a diseased tree.

It’s essential to identify the fungal disease invading your tree. The last thing any homeowner wants is a disease spreading to their healthy trees. Infection can spread through the soil, air, rain, and even contaminated pruning tools.

We have shared ten diseases in pine trees to help you identify what may be ailing your pine tree species. Some infections are more severe than others and affect different pine tree types. Keep in mind that a professional arborist should make any diagnosis.

1. Annosus Root Rot

Annosus Root Rot
Annosus Root Rot. Credit: Jason Hollinger, CC BY 2.0

This fungal disease stunts needle growth and causes a decaying condition called “butt rot.” Annosus root rot is a concern in pine plantations where thinning has occurred. The freshly cut stumps following thinning encourage the spread of this disease. Although this disease leads to death, there is a solution to prevent it from spreading to healthy pines.

Pine trees affected: This disease affects loblolly, slash, and white pines the most. Annosus root rot occasionally infects shortleaf, longleaf, Ponderosa, western white, lodgepole, whitebark, jack, pond, red, pitch, sand, and Virginia pines.

Symptoms: Substantial stump decay will occur. The roots and butt develop a soft, stringy, white rot. The fungus may generate conks, or fruiting bodies, at the base of the trunk. These fruiting bodies vary in shape and are between gray-brown and dark-brown in color on their surface, and white underneath.

Causes: The fungus, Heterobasidion annosum, spreads the most when stumps are freshly cut. Wind or splashing rain can carry the fungus from infected stumps to healthy trees that have cut surfaces. After landing, the spores then penetrate the wood to establish an infection. Infections can remain latent for decades before resuming growth in the pine tree. Stumps and trees with annosus root rot can also infect healthy trees through their roots.

Treatment: Common borax powder applied to the surfaces of freshly cut stumps will help prevent the spread to neighboring trees. Apply the borax powder in a salt shaker manner.

Seasons: Harvesting pines during dry summer and fall months lowers the possibility for spread.

Risk level: This disease is most concerning in forests following thinning, an operation that removes rows of trees. Trees of all ages can die from this disease, and volume losses from butt rot will occur in some species. In pines, death occurs after extensive decay.

2. Brown Spot Needle Blight

This disease is a large problem for longleaf pine seedlings and Afghan pines grown in Christmas tree nurseries. Symptoms occur months after infestation and can spread rapidly in permitting weather conditions.

Pine trees affected: This disease affects longleaf, Afghan, mugo, Japanese black, Virginia, eastern white, red, Austrian, and Scots pine.

Symptoms: Symptoms first appear in the fall as circular gray-green spots on the pine needles. The spots then enlarge and form narrow brown bands encircling the needles. The needles then die and fall off.

Causes: Brown spot needle blight is caused by the fungus Mycosphaerella dearnessii. Infections spread in wet weather when spores attack several times throughout the season. The splashing of rainwater enables the spores to spread rapidly and infect large areas of the tree. Contaminated pruning tools can also spread this disease.

Treatment: Prescribed and managed fire burning every two or three years eliminates the infected needles and kills the infectious spores. Professional fungicide sprays can also control the fungus. The Michigan State University Extension recommends applying fungicide when new needles are about half-grown between May and June and to apply a second spray three weeks later.

Seasons: Symptoms appear in the early fall.

Risk level: Nursery seedlings are most susceptible to infection when in the grass stage and will often die from brown spot needle blight. The disease can kill young pine trees that have been infected year after year.

3. Cotton Root Rot

This fungal disease is also known as Phymatotrichum root rot, Texas root rot, and Ozonium root rot. The disease infects more than 2,000 species of plants and is one of the most challenging fungal diseases to control. Cotton root rot is most prominent in the Southwestern United States.

Pine trees affected: Pines exposed to high temperatures and alkaline soils or soils of limestone origin are most susceptible, such as Afghan pine.

Symptoms: Symptoms begin with a slight yellowing or bronzing of the host’s leaves. After three days, permanent wilting occurs, followed by death. Trees and shrubs will succumb to the disease more slowly. Affected areas appear as circular patterns of dead plants and can gradually enlarge over time.

Causes: Cotton root rot is caused by the fungus Phymatotrichum omnivorum. The fungus invades new areas by slow growth through the soil from plant to plant. The fungus can survive in the soil for many years and as far as 8 feet deep in the ground.

Treatment: Cotton root rot is one of the most difficult plant diseases to control. One solution is to plant a resistant grass crop around the infected area. The resistant crop creates a barrier that limits the spread of the disease. If cotton root rot is infecting your pine, there is a chance of saving the tree if the decay is not yet substantial. The Oklahoma State University Extension recommends covering a ridge of soil around the tree’s drip line with a 2-inch layer of organic matter or cow manure. Then, scatter ammonium sulfate and sulfur over the manure. Flood the basin with enough water to soak the soil to a depth of 3 feet. Keep the soil moist for several weeks after treatment. The tree is likely to recover within the season.

Seasons: Symptoms usually occur from June through September when soil temperatures reach 82 degrees Fahrenheit.

Risk level: This fungal disease can survive in the soil for many years and kill even your tallest pine trees.

4. Damping-Off

A pine tree seedling shows signs of damping off.
A pine tree seedling shows signs of damping off. INAKAVillage211, CC by SA 3.0

A variety of pathogenic fungi, including Pythium sp., Rhizoctonia sp., Sclerotium sp., Fusarium sp., and Cylindrocladium sp., cause damping-off. Proper prevention methods are the only way to save your pine seedlings from this disease. These pathogenic fungi usually live on dead organic matter in the soil.

Pine trees affected: Damping-off affects many plant seedlings. Most types of pine tree seedlings are susceptible to this disease.

Symptoms: Seedlings failing to emerge from the soil is a symptom of damping-off. If emerged, the lower stems of the seedling will collapse, and the seedling limps over. Seedling stems may appear water-soaked, soft, mushy, and discolored. Roots may appear absent or stunted.

Causes: These pathogenic fungi can attack young seedlings above, below, or at the soil line. The disease is most active in wet, moist soils. Pine seedlings are susceptible to the disease for a short period and will outgrow their vulnerability. Wind, insects, and water can all carry the infectious spores to the soil. Dirty hands, contaminated tools or hose ends can also add pathogenic fungi. Once introduced to the environment, the pathogens move from plant to plant. Low light, overwatering, and over-fertilization can all contribute to increased levels of damping-off.

Treatment: Prevention is the best way to control damping-off in plant seedlings. Landowners can opt to buy pine seedlings for sale from nurseries with light, sandy soils that are less susceptible to pathogen growth. Raise the seedbeds so that they drain after irrigation and don’t remain too moist. Mulching the seedbeds with pine needles is also a prevention method. Fumigate the soil with an approved soil fumigant before planting or treat the seeds with a seed protectant fungicide.

Seasons: Soil temperatures for damping-off vary depending on the pathogenic fungus.

Risk level: Damping-off is a common and fatal disease that affects all types of plant seedlings.

5. Diplodia (Sphaeropsis) Tip Blight

Formerly Sphaeropsis blight (fungus – Sphaeropis sapinea), Diplodia tip blight (fungus – Diplodia pinea) attacks trees of all ages.

Pine trees affected: This disease attacks two-or-three-needled pines such as Austrian, red, mugo, and Scotch.

Symptoms: Needles begin to brown, yellow, or gray at the tip and will appear short and stunted. Small, black pycnidia (fruiting bodies) develop on needles, cones, or shoots. Cankers on stems and branches may also develop, as well as oozing resin.

Causes: The fungus overwinters in infected needles, cones, and tissue. From March through September, during wet conditions, the pycnidia release brown spores that wind, water, and animals spread to healthy trees. The fungus then germinates on the needles and kills the tissue soon after invading. The fungus may enter the needles or the tree through wounds caused by feeding insects, weather, or even pruning. In the second year, cones become infected and subsequently spread the disease.

Treatment: Prune infected twigs, branches, and cones during dry weather. Remove and burn or bury the contaminated materials to prevent further spreads. Michigan State University recommends applying appropriate fungicides in early spring.

Seasons: Diplodia tip blight is present year-round. The fruiting bodies appear in summer.

Risk level: If a canker infection becomes severe, it may kill wood tissue and significant parts of the tree. This disease causes the most considerable damage to trees more than 30 years old. Rarely attacks trees under 15 years old, but can be harmful to young seedlings.

6. Dothistroma Needle Blight

This disease is also called red-band needle blight.

Pine trees affected: This disease causes the most damage to Austrian pine and Ponderosa pine. Red, mugo, and Scotch pines are also susceptible.

Symptoms: Between March and April, the needles on the lower part of the tree begin to turn brown. Needles over 20 feet high are rarely affected. The needles turn brown at the tip while the base of the needles remains green. As the dead brown areas encircle the needles, a reddish-brown band appears to form around the needles’ remaining green. Black fruiting bodies, stromata, can be seen in the bands of the needles.

Causes: The fungus Mycosphaerella pini causes Dothistroma needle blight. The stromata rupture through the epidermis of infected needles and release infectious spores. The spores are then spread by the wind or rain and infect healthy needles throughout the growing season.

Treatment: The University of Minnesota Extension recommends applying copper fungicides once before buds open in the spring, usually in mid-May. And then once again when needles have grown to their full length in the summer. Pruning infected branches and moving sprinklers away from pine needles also reduce the spread of this disease.

Seasons: New infections typically appear in late summer and fall.

Risk level: This fungal disease kills needles of all ages and can weaken or eventually kill your pine trees. It is a slow-moving disease that takes a full year to complete its life cycle. It often takes years of repeated infection to develop a severe problem for your tree.

7. Fusiform Rust

This fungal disease requires two hosts to complete its reproductive stages: pine and oak. Early rapid tree growth, warm moist conditions, and the alternate host’s presence increase the possibility of infection. Fusiform rust is a severe disease affecting seedlings in nurseries and fields in the southern United States.

Pine trees affected: Slash and loblolly pine are common hosts to this disease. Longleaf is moderately resistant.

Symptoms: The development of galls, spherical or linear swellings, on branches and the trunk are a sign of fusiform rust. Stem breakage at the gall is common. Galls may develop into open cankers, which are sunken, injured, brownish-red lesions.

Causes: The fungus Cronartium quercuum causes fusiform rust. The fungus produces five different spore stages and requires both an oak and a pine tree to complete its life cycle. Aecia, appearing as yellow-orange blisters, develop on the surface of galls in early spring. The aecia then rupture and produce yellow-orange spores called aeciospores. The spores do not infect the pine but instead affect the leaves of healthy oaks after the wind carries them. Infected oak leaves will have yellow spots, but symptoms on oak leaves can go unnoticed. The infected leaves then develop red-brown, hair-like structures called telia, telial columns, or telial horns. The telia produce teliospores, which then germinate and create spores called basidiospores or sporidia. Carried by the wind, these sporidia create infections in vulnerable pine tissue.

Treatment: To treat fusiform rust, landowners can remove the galls by pruning or removing infected trees. Seedling nurseries can control this disease with fungicides. The Alabama A&M and Auburn Universities Extension advise that landowners who plant seedlings make sure the nursery treats the pine seedlings for fusiform rust. Seedlings infected in the nursery will not survive more than a year or two.

Seasons: The aecia appear on galls in early spring.

Risk level: Young pine seedlings infected with fusiform rust will die a few years after leaving the nursery. Those that survive will grow deformed. Older trees that survive infections may develop a sunken canker. Cankers on stems can make a stem vulnerable to breaking in high wind.

8. Needle Rust

Needle rust needs two different host plants to complete its life cycle. One is from the pine family, and the other is from the aster family.

Pine trees affected: Affected pine trees include, but are not limited to, Austrian, jack, red, Ponderosa, mugo, and Scots.

Symptoms: The first sign of the disease occurs when small yellow-orange spots form on the needles. In spring, the spots develop white, spore-producing pustules called aecia. By late spring or early summer, the aecia erupt and release pinkish-orange spores. Infected needles may remain attached for several years, but will die of severe infection.

Causes: The fungus Coleosporium asterum causes needle rust. After the pinkish-orange spores erupt from the aecia in small puff clouds, they cannot infect other pine needles. They are instead carried by the wind to infest the leaves of an aster tree. The diseased aster leaves then develop yellow-orange spores that infect other aster leaves throughout the summer. In the fall, the aster leaves produce a dark brown spore, which the wind transports to infect neighboring pine needles.

Treatment: Needle rust causes minimal damage. To increase your infected tree’s health, water your trees during dry conditions and mulch to preserve moisture in the soil.

Seasons: Needle rust’s life cycle begins in the fall when pine needles are first infected. By early spring, the aecia have produced spores to infect adjacent aster leaves. Once fall arrives, the spores developed in aster leaves are released to reinfect the pine needles.

Risk level: Severe damage is seldom.

9. Pine Wilt

Pine wilt is a lethal disease caused by the pine wilt nematode Bursaphelenchus xylophilus. The pine sawyer beetle carries the nematode to its host. The nematode requires high summer temperatures to develop in the beetle and within the tree.

Pine trees affected: Exotic pines, including Scots, Austrian, mugo, and Japanese red, are susceptible to infection.

Symptoms: The needles are the first part of the tree to show signs of pine wilt. They turn a grayish-green, and then a yellow and reddish-brown. The tree will die within a few weeks or months after turning this color.

Causes: Pine sawyer beetles carry pine wilt nematodes from diseased trees to healthy trees. Once the beetle arrives at the susceptible tree to feed, the nematodes enter the tree through the feeding wounds left by the beetle. The nematodes can also infect the host when the beetle lays eggs. The nematodes then multiply within the tree and block the pine’s water transport system.

Treatment: Landowners must remove the infected pine tree immediately. Chip, burn, or bury the diseased wood before the emergence of pine sawyer beetles in late June. Do not save any infested timber for firewood or transportation. The Extension at Colorado State University recommends two nematicidal avermectin compounds to treat pine wilt. These compounds target nematodes by killing or immobilizing them. This treatment does not kill the pine sawyer beetle. A professional arborist can inject these compounds into the pines to prevent pine wilt. The procedure is not, however, useful if the tree is symptomatic or if the nematodes have already colonized the tree.

Seasons: Most pine wilt deaths occur in late summer or fall.

Risk level: If landowners have not executed prevention methods, pine wilt will kill infested trees. There is no treatment to kill the pine sawyer beetle. Once the nematodes have invested the pine tree, treatment is too late. The best solution is to prevent further infestation in adjacent trees.

10. Pitch Canker

Pitch canker occurs in the southeastern United States, Mexico, Chile, Japan, South Korea, Italy, France, Spain, Portugal, and South Africa.

Pine trees affected: Pitch canker affects many pine species, including Bishop, knobcone, gray, coulter, Torrey, and Ponderosa. Monterey pine is the most widely affected host.

Symptoms: This disease creates infected lesions that can encircle branches, exposed roots, and trunks. The tips of affected branches wilt due to lack of water flow. After the needles turn from yellow to brown, the needles fall off. The fungus doesn’t move within the tree, so each canker or lesion is a separate infection. The pitch, also called resin, begins to cluster on the infected site. Removal of the bark reveals a honey-colored resin-soaked wood. The honey-colored resin can flow along the bark to coat areas several feet below the infected lesion.

Causes: The fungus Fusarium circinatum causes pitch canker. Engraver beetles can further damage diseased pine trees and cause the death of branches or the entire pine. The resin flow often attracts pitch moths, whose infestation can create a bulging mass of accumulated pitch. Insects spread the disease from tree to tree as they feed.

Treatment: The best approach to pitch canker is to prevent the fungus from moving to your healthy trees. If a pine tree is not severely infected, landowners can limit the spread by removing infected branches. It is essential to perform any pruning with sanitized tools. Insecticides are not an effective way to control pitch canker, and there are no direct methods that control or treat the disease.

Risk level: Pitch canker may result in severe damage or death of your pine tree. Yet not all infected trees will become highly diseased, and some may even recover from acute infection. The University of California Agricultural & Natural Resources says experiments show that Monterey pines repeatedly exposed to pitch canker may develop resistance. The University recommends landowners consult an arborist before removing diseased trees, as there is a possibility for recovery.

When to Call a Professional

Consulting a professional, licensed arborist near you is an essential first step to save your pine tree. If you notice any symptoms in your pine tree, call a tree care professional right away. When pine tree diseases go ignored, they may become fatal and infest adjacent pines.

A certified arborist can apply treatments and remove infected trees. Arborists can even assist homeowners before symptoms occur by performing preventive disease measures. It’s never too early to call a professional arborist, but it can be too late.

Main Photo Credit: Irina Iriser / Pexels

Jane Purnell

Jane Purnell

Jane Purnell is a freelance writer and actor in New York City. She earned her B.A. from the University of Virginia and enjoys a warm cup of French press coffee.