“Everything was normal and then May arrived,” said Jenny Glass, plant diagnostician at the Washington State University plant clinic.
The cool, moist spring created ideal conditions for the disease rampage that has damaged many trees and shrubs. Cold temperatures last winter also affected numerous plants.
Many cherry, flowering plum, London plane, sycamore, hawthorn and willow trees have lost many of their leaves. The culprits range from various leaf diseases to insect pests. In some instances, like the purple leaf flowering plums, it may have been a triple whammy: two diseases and aphids.
Unfortunately, it is too late to treat the problems this year. But, trees are tough. Many that have lost most of their leaves have already started to grow a new crop. Since the disease-spreading season is over, the new food producing leaves will be healthy.
However, if next spring is cool and moist, the cycle may repeat itself. That is why it is critical to properly identify the problems, determine which treatments are recommended and apply them at the proper times. Spraying anything whenever one feels like it does not cut the mustard.
One of the best sources is the WSU Cooperative Extension Web site. Type the word “hortsense” in a search box on a computer. Click on the WSU Web site. A list of topics will appear on the left side of the page. To address problems with ornamental trees, for example, click on “Ornamentals.” Then select the species of choice.
A list of insects and diseases that attack the selected species will appear. Click on a pest and a page describing the disease or insect, non-chemical and chemical control options will be displayed. Specific pesticide recommendations are listed by their brand names.
Other sources include Master Gardener clinics scattered throughout the area. To find locations, dates and times, search www.pierce.wsu.edu/mg, then select “Clinics.” Take samples of healthy and diseased twigs or be able to describe the damage and species affected to the Master Gardeners on duty.
Other excellent sources include arborists that specialize in tree and shrub problems and will visit and inspect homeowner’s landscapes.
Ornamental cherries and plums: Holes in leaves are caused by “shothole” or Coryneum blight. Apply fungicides at leaf fall in late autumn and in the spring after flower petals have fallen.
Brown rot fungus is very common on cherries and is difficult to control. It causes blossoms and twigs to die. Infected blossoms often remain attached and spread the disease to twigs and branches. Diseased twigs may die or develop cankers and dead leaves in the summer. These are highly visible at present. Apply fungicides three times during the bloom.
Plum leaves that curl or “crinkle” are caused by the feeding of the leaf curl plum aphid. Some tiny adults or cast skins are still visible inside the curled leaves. Oils or fungicides must be applied early before the leaves begin to curl.
Note: specific chemical recommendations are listed on the Hortsense Web site discussed above.
Sycamore and London plane trees: Sycamore anthracnose causes brown and crinkled leaves. During wet, cool springs such as this year, the fungus can cause nearly total defoliation. Fungicides can be applied during bud swell and again two weeks later.
Photinia shrubs and hedges: This very common “leaf spot” fungus causes red to purple spots on the leaves in the spring and can cause defoliation. Fungicides can be applied in early spring on the waxy red colored new growth.
Last winter’s cold temperatures also caused severe defoliation. Fortunately, new buds and leaves can be observed growing on many of the damaged plants.
When reacting to a problem, there are three choices: spray it, live with it or remove it.
If choosing to treat a problem, identification is required to select the proper application. If one wishes not to apply pesticides, then removal may be an option.
Personally, I generally select the middle course and choose to live with the problems. My infected cherries and photinia hedge are already growing new, healthy leaves. They will soon look fairly normal and be attractive for the remainder of the summer.
Dennis Tompkins is a certified arborist, hazard tree risk assessor, Master Gardener and urban forester from the Bonney Lake-Sumner area. He provides small tree pruning, pest diagnosis, hazardous tree evaluations, tree appraisals and other services for homeowners and businesses. Contact him at 253-863-7469 or e-mail at firstname.lastname@example.org. Web site: evergreenarborist.com.