Why Are My Pine Needles Turning Brown?

Pine trees are medium to large sized evergreens valued for their hardwood timber and longevity. Premature browning of pine tree needles is a common symptom for various pine disorders, including disease, insect and nematode infections. Early identification and control of these pine tree disorders is vital for preventing serious damage.

Pine wilt

Pine wilt is a serious condition of pine trees, caused by the pine wilt nematode. Nematodes are small, microscopic roundworms that feed on the cells of pine trees. Unlike most nematode pests that thrive in soil and infect plant roots, pine tree nematodes only infect the above ground tree parts. The nematodes damage water-conducting tissue, resulting in brown needles and rapid tree death. Remove and burn infected trees to prevent the nematodes from spreading to healthy trees. Chemical nematicide is an effective, but costly method of control for infected pines.

Phytophthora root rot

Phytophthora root rot is a serious soil borne fungal disease of pine that affects the vitality of the tree. The fungus infects the pine roots below the soil. However, above ground symptoms diagnose infection. Symptoms consist of red to brown needle discoloration, branch death, reduced vigor, needle drop and tree death. The disease favors poor draining soil, free soil moisture and warm temperature conditions. Prevent the disease by planting pine in well-drained soil, avoid overwatering and avoid planting in infected soil. Private labs and university-based labs can test soil for the fungus before planting. Chemical fungicides are an effective method of reducing infection rates of Phytophthora root rot.

Diplodia tip blight

Diplodia tip blight of pine is a fungal disease of pine that affects the trees needles and vitality. The fungus, Sphaeropsis sapinea, causes needle discoloration from yellow to brown, reduced needle growth, girdling and tree death. Girdling occurs when the fungus infects open wounds on pine, which eventually leads to tree death if left untreated. The disease favors heavy rainfall and open wounds, during the spring months for infection. Maintain tree vigor with regular watering, fertilization and avoiding pruning wounds to prevent infection. However, chemical fungicides are an effective method of control.

Pine bark beetle

Pine bark beetles are insect pests of unhealthy pines that cause serious damage to a variety of pine species. The beetles tunnel within the bark, which prevents water and nutrients from moving throughout the tree. While there are several pine bark beetle species, symptoms are similar. Symptoms consist of squiggly lines on the outside of the tree bark, yellow to brown needle discoloration, needle drop and tree death. Increase tree vigor with regular watering deep in the soil and regular fertilization to prevent infestation. Cut down and burn infected trees to prevent the beetle from spreading to other pines.

Sources:

http://lancaster.unl.edu/hort/articles/2004/pinewilt.shtml
http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/odin13/od13.htm
http://www.uri.edu/ce/factsheets/sheets/diplodiapine.html
http://www.spokane-county.wsu.edu/spokane/eastside/Fact%20Sheets/C097%20Pine%20Bark%20Beetle%2005.pdf