egg masses. Past eradication treatments have 

 been successful and, fortunately, neither the 

 European nor the Asian gypsy moth has be- 

 come established in the Pacific Northwest. The 

 gypsy moth, however, is constantly being re- 

 introduced, so annual monitoring is necessary. 



Dogwood anthracnose disease causes leaf blight, 

 branch dieback, and tree death of ornamental 

 and native dogwoods. 



Dogwood anthracnose has become estab- 

 lished in the Pacific Northwest — ^Dogwood 

 anthracnose, a very destructive disease of flow- 

 ering dogwood, first appeared in the eastern 

 United States in the early 1970s. It was first 

 reported on native Pacific dogwood in Wash- 

 ington in 1976 and in Oregon in 1983. As of 

 1994, the disease was present on Pacific dog- 

 wood in most western Oregon and Washing- 

 ton counties. Evidence suggests that this dis- 

 ease was introduced from abroad, but its origin 

 remains unknown. 



The disease causes leaf blight, branch die- 

 back, and tree death on Pacific dogwood and 

 several ornamental cultivars, and it is of par- 

 ticular concern in ornamental landscapes. The 

 greatest hope for long-term disease manage- 

 ment is to develop disease-resistant dogwoods. 



Environmental stresses affect urban 

 trees — ^Environmental stresses, such as too 

 much or too little water, affect the health of 

 trees in communities. Urban forests generally 

 lack the complex forest floor that helps trees 

 retain moisture and nutrients. Drought over 

 prolonged periods can reduce the vigor of ma- 

 ture trees and increase their susceptibility to 

 insects and disease. Supplemental irrigation, 

 even for established trees, is beneficial during 

 dry, hot weather, but too much water can also 

 be detrimental. Excessive summer irrigation, 

 for example, leads to root rot and structural 

 instability in Oregon white oaks. 



Building and maintaining cities affects tree 

 health. Many existing tree health problems can 

 be traced to soil compaction and root damage 

 during construction, utility trenching, or power 

 line clearance. Decay organisms enter me- 

 chanical wounds and can create hazard trees. 

 Pollution caused by automobile and industrial 

 emissions also affects the health and longev- 

 ity of community forests. 



Proper care and species selection will im- 

 prove the health of urban trees— The care- 

 ful observation and inventory of urban trees 

 will detect many disease and insect problems. 

 Given adequate funding, many can be treated. 

 A diversity of tree species lessens the risk of 

 catastrophic losses from weather extremes or 

 introduced pests. Choosing the right tree for 

 the right place, and regular pruning to remove 

 dead wood and excessive twig growth will help 

 keep trees healthy. As urban forests mature, 

 the loss of older trees is inevitable. If commu- 

 nities maintain mature trees and plant new 

 trees, their forests will be healthier and future 

 generations will enjoy a thriving urban forest. 



Urban— 64 



