Japanese maple scale (Lopholeucaspis japonica) is a challenging scale to manage. In the United States, it was first found on the east coast, but is rapidly expanding its range. Japanese maple scale's small size, ability to blend in, and long crawler emergence period make it difficult to control. It is a pest primarily of nurseries and is often on hollies. Holly’s tight shrub-like habit makes sprays difficult to accomplish properly.
This is a difficult scale to control for multiple reasons. First, its crawler emergence occurs over a period of several months. This means that applications made before the crawler has emerged are not affective. Second, crawlers begin secreting their waxy coating within three days of hatching. This is a very small window for treatment. Third, the scale is very small, and can blend in with bark very easily, making scouting difficult. Hort. Oil + Distance is and industry standard, though Transtect as a foliar application, and Transtect as a soil application or lower systemic bark spray application have also been shown effective.
Other Treatment Practices
- Inspect new plant material before introducing it to the landscape.
- Cultural practices like root collar excavation, correct mulch, managing irrigation, etc. will help trees recover from infestation after treatment.
IGRs work well, but may take up to three sprays to get reliable control. Studies have shown Transtect as a soil application as a viable control method.
Signs of Damage
- Branch dieback
- Waxy scales are about 1 mm in length
- Dark scale cover can be seen when wax is rubbed off, or if oil is applied
- Immatures and eggs are purplish
Photo: University of Maryland
Trees At Risk
*denotes those most susceptible
- Eggs are laid in April/May.
- Two overlapping generations. Crawlers emerge in May/August.
- First generation emerges as smoke bush or oak leaf hydrangea blooms; 2nd generation emerges when Arailia spinosa is in flower bud swell.
- First generation crawlers begin to emerge at 816 GDD and peak at 1143GDD(emerge over an 8 week period); second generation crawlers begin to emerge at 2500 GDD and peak at 3022GDD(emerge over a 7 week period).
- Within hours the crawlers settle down and create covers.
- Overwinter as 2nd instars.
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.