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The following is adapted from the University of California?EUR??,,????'?????<www.ipm.ucdavis.edu and from Kansas State University?EUR??,,????'?????<www.oznet.ksu.edu and www.berkeley.edu.
Due to climate and geography, each region of the country has diseases that pose unique problems for local trees. Here are four of particular concern for West Coast contractors and arborists. Anthracnose and wood decay fungi, however, can be problems anywhere in the country.
For new plantings, choose varieties that are resistant to the anthracnose fungi. Plant them widely apart to maximize air circulation and increase sunlight, both of which facilitate faster drying of leaf surfaces when trees are fully grown. Once symptoms develop or become severe, anthracnose cannot be effectively controlled during the current season.
Rake and dispose of fallen leaves and twigs during the growing season and during the fall. Prune during winter to increase air circulation in the canopy and remove the previous season?EUR??,,????'?????<
Chemical sprays normally are not necessary to control anthracnose. Occasionally, trees with a history of anthracnose may require treatment for aesthetic purposes. Several fungicides are labeled for certain anthracnose diseases. Additionally, several fungicides are labeled for systemic injection for anthracnose control.
Environmental factors also play important roles in managing anthracnose. Pay close attention to past and current conditions such as rain and irrigation to determine if anthracnose development is favored. Dry spring weather could mean that disease management is not necessary. A wet spring or an irrigation system that wets the foliage could result in disease outbreak that may warrant control.
Sudden oak death is the name given to an epidemic, first detected in 1995, that affects three true oak species?EUR??,,????'?????< Additional species affected include rhododendron, madrone, California huckleberry, California bay laurel, California buckeye, big-leaf maple, toyon and manzanita. A fungus-like organism, Phytophthora ramorum, has been identified as the infectious agent. While no chemical treatments are proven to reverse the disease, a U.C. Berkeley study shows that a phosphite compound sold as AgriFos and ArborFos can slow or stop the organism from growing if applied early enough. The chemical is not a cure-all, but may be able to save individual trees in infected areas. ?EUR??,,????'?????< Tree fungus of several varieties usually affects older or damaged trees.Photo:www.ipm.ucdavis.edu Fungal Infestation/Wood Decay Wood decay is usually a disease of old, large trees. It is very difficult to manage, but a number of factors can reduce the risk of serious damage. First, trees should receive proper cultural care to keep plants vigorous. Minimize wood decay by protecting plants from injuries. Properly prune young trees to promote good structure and avoid the need to remove large limbs from older trees, which creates large wounds. Cut out dead or diseased limbs. Make pruning cuts properly: prune just outside the branch bark ridge, leaving a collar of cambial tissue around cuts on the trunk to facilitate wound closure, but avoid leaving stubs. Make cuts so that rainwater will drain.
Additional species affected include rhododendron, madrone, California huckleberry, California bay laurel, California buckeye, big-leaf maple, toyon and manzanita.
A fungus-like organism, Phytophthora ramorum, has been identified as the infectious agent.
While no chemical treatments are proven to reverse the disease, a U.C. Berkeley study shows that a phosphite compound sold as AgriFos and ArborFos can slow or stop the organism from growing if applied early enough.
The chemical is not a cure-all, but may be able to save individual trees in infected areas.
?EUR??,,????'?????<
Wood decay is usually a disease of old, large trees. It is very difficult to manage, but a number of factors can reduce the risk of serious damage.
First, trees should receive proper cultural care to keep plants vigorous. Minimize wood decay by protecting plants from injuries. Properly prune young trees to promote good structure and avoid the need to remove large limbs from older trees, which creates large wounds. Cut out dead or diseased limbs. Make pruning cuts properly: prune just outside the branch bark ridge, leaving a collar of cambial tissue around cuts on the trunk to facilitate wound closure, but avoid leaving stubs. Make cuts so that rainwater will drain.
Pitch canker is a disease of pine trees that is caused by the fungus Fusarium circinatum. Douglas fir can also be infected, but this is rare and infected trees are not severely damaged.
The disease was first observed in California?EUR??,,????'?????<
Most pines native to California are susceptible to pitch canker, but Monterey pine (Pinus radiata) is the most widely affected host. Pruning does not slow the spread of the disease in a highly infested area. However, pruning can be used strategically to enhance the aesthetic quality of a tree and thereby delay its removal from the landscape.
Spider mites can be found in most species of spruce but are predominately found on Colorado or white spruce. Spruce spider mites are tiny and very difficult to see. They are approximately .5 millimeters and are a dark green to dark brown in coloration. The best method to find out if your spruce tree may have mites is to place a white piece of paper under a branch and shake it repeatedly. Fold the paper in half, if red smears appear after opening the paper, chances are you have spider mites living in your trees. Ensure you check your trees on a regular basis as mite populations can grow quite rapidly. ?EUR??,,????'?????<
3,000,000: Trees affected by an outbreak of Dutch elm disease in Britain in 1975. Source: www.bbc.co.uk
1: The number one deadly coniferous tree disease is?EUR??,,????'?????<Source: www.forestry.about.com
Francisco Uviña, University of New Mexico
Hardscape Oasis in Litchfield Park
Ash Nochian, Ph.D. Landscape Architect
November 12th, 2025
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