File under “if it’s not one thing it’s another...” Japanese Maple Scale (JMS) (Lopholeucaspis japonica) has been around for decades but seems to be of increasing concern for nurseries and landscapes. The armored-scale pest damages plants with piercing-sucking mouthparts, causing cells to rupture/collapse, resulting in eaf drop and branch dieback. Moreover, it is a pest of a very wide range of woody ornamentals (over 45 genera), including Buxus. Understanding the life cycle of JMS is critical to identification and management - see below for resources explaining the complexity thereof.
Infestation of Japanese Maple Scale on an interior branch of boxwood. Note the elongated white scale "armor." Photo courtesy of J. Bennett Saunders.
The armored cover of an adult has a waxy coating rendering treatment difficult. This coating (called a “test”) may also make identification as it is similar in appearance to other scales. Compounding the issue: multiple life stages can be present at once, and multiple generations accumulate and build in older interior wood. Cooler areas see two generations; warmer mid-South areas may see more. Stanton Gill, IPM and Entomology Specialist with University of Maryland Extension, has been working on regional JMS for quite a while. It has since made it as far west as Indiana and Ohio, according to Gill. Bennett Saunders noted he’s seen it impact primarily two Buxus sempervirens cultivars - ‘Dee Runk’ and ‘Fastigiata.’
Japanese Maple Scale damage, including branch die-back, on Buxus sempervirens ‘Dee Runk’
We asked Gill for a status check at the end of August: “We are in the middle of the second generation [and it] appears to be on the increase in the nursery trade this season.” Along with the eponymous host, Gill and colleagues are receiving reports of it in both nurseries and landscapes on boxwood, blue holly [Ilex x meserveae and cultivars] and American holly [Ilex opaca and cultivars]” among other taxa. Gill reiterated the very wide host range and urged nurseries and landscapers to be vigilant. Degree days and careful scouting can be used to detect the crawler stage - the non-armored, most vulnerable stage of development that responds to chemical control measures.
One means of control is mechanical - high-pressure water spray, along with a gentle scrub brush - and one of the best options for homeowners who may have a few shrubs or trees with lower levels of JMS. There are also parasitoids (beneficial insects) that attack JMS - their presence can be detected by tiny holes piercing the scale covers. In order to preserve populations of beneficials, don’t utilize topical insecticides - there are other options.
For the current situation in nurseries or professionally-managed landscapes, Gill says “Distance and Talus are two good Insect Growth Regulators (IGRS).” In late fall (no tender leaves on boxwood), he recommends coming back with a 1 - 2% horticultural oil to go after the overwintering second instar males and females. Due to potential phytotoxicity, always test oils on a small number of plants before more extensive application. Read and follow all pesticide label directions carefully.
The above recommendations are based on the Mid-Atlantic location, always check your state’s Cooperative Extension pesticide management information for management recommendations and adjust the timing for your locale. For more information on Japanese Maple Scale, please check out these resources:
Boggs, J. 2020. Japanese Maple Scale (JMS). https://bygl.osu.edu/index.php/node/1554
Frank, S. 2017. Japanese maple scale management. Nursery Management. https://www.nurserymag.com/article/japanese-maple-scale/
Frank, S. 2017. Take up arms. Nursery Management https://www.nurserymag.com/article/take-up-arms/
Gill, S. and P. Shrewsbury. 2021. Japanese Maple Scale: A Pest of Nursery and Landscape Trees and Shrubs (FS-967) https://extension.umd.edu/resource/japanese-maple-scale-pest-nursery-and-landscape-trees-and-shrubs-fs-967
Any reference to commercial products, trade, or brand names is for information only, and no endorsement or approval is intended. Always refer to tables and information in your state’s Pest Management Guide for active ingredients and trade names of any chemical products. State regulations may vary - always remember “the label is the law.”