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Plant NameTypeDescription 
Bacterial blightCotoneasterDiseaseBacterial blight symptoms first appear in the spring (April-May) as brown spots on young stems and leaves, followed by wilted and blackened new growth. The disease is especially favored by wet conditions. Infection often occurs at injury sites, such as those caused by frost damage or pruning wounds. The bacterium causing the blight also infects many other hosts, including lilac and maple. Bacteria are easily spread by splashing water and pruning tools. Bacterial blight may be confused with fire blight.
Fire blightCotoneasterDiseaseFire blight is a bacterial disease which initially infects via flowers. Common symptoms include watersoaked spots on the bark, cankers at the base of affected twigs, and droplets of a dark bacterial ooze on the bark. Affected shoots often appear black and "scorched", wilt, and develop a characteristic "shepherd's crook" appearance as they die. The disease is easily transmitted by rain, wind, tools, and pollinating insects. Fire blight may also infect apple, pear, pyracantha, and crabapple. Bacterial blight caused by Pseudomonas may be mistaken for fire blight. Fire blight is not a problem in western Washington.
ScabCotoneasterDiseaseSymptoms of scab on cotoneaster are similar to those on apple. A fungal disease, scab causes leaves and fruit to develop dark or black blotchy spots. Initially, the leaves show pale pinhead spots, which later darken to a velvety olive then black. The diseased leaves are often curled, puckered, or otherwise distorted. Affected leaves may turn yellow prematurely. Moist conditions favor disease development.
Cotoneaster webwormCotoneasterInsectThe cotoneaster webworm is a dark brown caterpillar, 1/4" to 1/2" long. It typically ties clumps of leaves together with webbing and feeds within the nests, skeletonizing leaves. The caterpillars feed during the summer and fall, overwintering in nests on the plant and pupating in the spring. The dark gray, night-flying adult moth emerges in the spring to lay eggs. The webworm is primarily a problem on Cotoneaster horizontalis (rock cotoneaster).
Spider mitesCotoneasterInsectSpider mites are tiny, eight-legged, and of various colors from yellowish to dark to red. They may be found on the upper or lower surface of leaves and often produce a fine webbing on the leaf surface or between leaf and stem. Spider mite feeding results in a very fine yellowish speckling or stippling on the leaves. Severe infestations may cause leaf yellowing and weaken plants. Spider mite infestations are often worse during dry, dusty conditions.