WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Scale

(Various species)

Insects & Invertebrates

 

Scale

 

Symptoms

Scale insects belong to the insect order Homoptera; members of this order are known for their honeydew secretion, which promotes the growth of sooty mold. When this fungal disease grows on the honeydew on the leaves, it can reduce photosynthesis and makes harvesting unpleasant. Furthermore, it can create secondary costs of washing the fruit before sales and can make the fruit unsuitable for fresh market sales. Scales attach their piercing-sucking mouthparts into the blueberry branches and siphon the sap thus reducing plant vigor and terminal growth.

 

Identification

Adult scale is seen as dark red to brown bumps, up to 1/4 inch (5mm) in diameter, usually on previous seasons’ growth. The live young, called crawlers, are inconspicuous, mite-sized with six legs and range in color from yellow to red. Overwintering scale are smaller than the adults and are pale in color.

 

Terrapin Scale

 

Life History

White eggs are found under the sedentary scale insect in May or June. Eggs begin to hatch in late June to early July and the crawlers migrate from under the female to the underside of leaves. They will feed on the leaves for 4 to 6 weeks before returning to the stems to overwinter; they insert their mouthparts to feed and secrete wax to form a shell. These overwintering forms complete their development by late spring or early summer of the next season. Scales mate in early spring and the females continue to feed until early fall. The males die after mating and do not harm the plant.

 

Monitoring

During the dormant season, inspect plants and mark areas where many scales are seen. Start to check for egg hatch and crawler migration in May. Double-sided sticky tape can be put around canes late in the dormant period to detect crawlers on branches. Inspection of fruit at harvest or in the packinghouse will indicate whether a problem exists.

 

Putnam Scale

 


Thresholds and Management

Threshold varies according to end product usage and processor. Processors of fresh market fruit have zero tolerance for honeydew on fruit. Talk to your buyer for their threshold. Prune out and destroy heavily infested branches. Scales may be rubbed off by hand for minor infestations. Scales typically occur in older fields on old wood, so regular pruning is the most effective control.

Dormant oil can be used when pruning is not a sufficient control; it should be applied before bloom. Use high pressure to ensure good coverage of the undersides of the leaves and twigs. Dormant oil kills scales by suffocation, therefore spray to the point of run-off to obtain good coverage.

Light summer oil can be applied during the growing season to control crawlers. Crawlers are usually active from late July through August.

 

Resources

Michigan State University, Blueberry Facts, Scales
http://www.blueberries.msu.edu/scales.htm

Oregon State University, Azalea Bark Scale
http://oregonstate.edu/dept/nurspest/azalea_bark_scale.htm

 

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WSU Whatcom County Extension • 1000 N. Forest St., Bellingham, WA 98225 • (360) 778-5800 • whatcom@wsu.edu