Magnolia scales, Neolecanium cornuparvum, are amongst the largest scale insects to infest shade trees, with some individuals reaching ½” in length. As the common name suggests, this scale is a frequent pest of magnolia species, including star, saucer, and the cucumber tree. A conspicuous pest in mid to late summer, they cause damage to trees by weakening and girdling branches while producing sticky ‘honeydew’ on leaves and targets below.
Treatment Strategy
Magnolia scale can be a challenging soft scale to control. Reports from arborists and university scientists have yielded inconsistent control from both crawler sprays and soil applied systemic treatments. The magnolia scales non-synchronized (crawlers hatch and settle for a prolonged period of time in late summer/early fall) life cycle makes timing of spray products operationally challenging.
Xytect can be applied in late summer/early fall (same time as fall insecticide sprays) of the previous year or Transtect can be applied during leaf emergence in early spring of the current year to kill overwintered instars. Proper timing and a combination of sprays and soil applied treatments may be required in the first year of treatment to get high pest infestations under control.
Dormant oil treatments can assist with control (should not be counted on as a stand-alonec ontrol) and should be applied in early spring. Foliar spray insecticides combined with 0.5% to 1.0% horticultural oil can be applied after the majority of the crawlers have hatched and settled in late summer/early fall.
Transtect Infusible or Xytect 10% as a tree injection treatment for trees that cannot be treated with foliar sprays or other systemic options.
Other Treatment Practices
- Promote health and vigor with proper irrigation, mulching, proper pruning and prescription based fertilization practices.
Limb/Foliar/Basal Bark Spray, or Soil Application Using Transtect
Tree Injection Using Transtect Infusible
Limb/Foliar Spray Using Proxite + RTSA Horticultural Oil
Soil Application or Limb/Foliar Spray Using Xytect 2F
Tree Injection Using Xytect 10%
Foliar Spray Using RTSA Horticultural Oil
Expected Results
Magnolia scale can be a challenging soft scale to control. Reports from arborists and university scientists have yielded inconsistent control from both crawler sprays and soil applied systemic treatments. The magnolia scale’s non-synchronized (crawlers hatch and settle for a prolonged period of time in late summer/early fall) life cycle makes timing of spray products operationally challenging.
Heavy magnolia scale populations will require two years of systemic soil treatments to reduce adult feeding and sooty mold production. Expect some adult feeding and sooty mold production in year one, if spring applications of Transtect or Xytect are applied.
A combination approach of a systemic soil treatment and a fall crawler stage foliar spray may be used to provide additional control of heavy initial scale populations. As scale population is reduced in following years consider applying a stand-alone soil treatment of Transtect in early spring or Xytect in late fall.
Since the females leave their hollow brown shells behind that stick to the plant for many months, check to see if scales are alive by crushing the shell. Live scales will “bleed” when crushed, dead scales will be dry and will not “bleed”.
Signs of Damage
- Sticky honeydew on leaves and targets underneath the infested tree
- Dwarfed or stunted growth on infested twigs
- Branch decline on severely infested twigs
- Newly hatched crawlers are a medium brown color, getting darker after feeding commences
- Crawlers are present in late summer/early fall
- Presence of large, oval shaped dark brown insects on twigs and branches, often in high population numbers in late spring/early summer
Photo: msu.edu
Photo: Wikimedia Commons
Trees At Risk
- Star Magnolia (Magnolia stellata)
- Saucer Magnolia (Magnolia soulangeana),
- Cucumbertree Magnolia (Magnolia acuminata)
- Lily Magnolia (Magnolia liliiflora)
It has also been reported that magnolia scale feeds on
- Daphne spp.
- Virginia Creeper (Parthenocissus quinquefolia)
- Tuliptree (Liriodendron tulipifera)
Biology
- Females produce eggs from mid-summer to fall.
- Eggs hatch August through October(1938-2800 GDD).
- The young scale –known as crawlers –move to one-to two-year-old branches where they feed, grow a protective shell, and overwinter.
- Feeding resumes as leaves emerge the following spring, producing a large amount of honeydew.
- As summer approaches, the females lay eggs and then die, leaving behind their hollow brown shell that persists on the plant for months.
- Magnolia scales produce one generation each year.
References
University of Kentucky
https://entomology.ca.uky.edu/ef431
The Ohio State University
https://ohioline.osu.edu/factsheet/ENT-61
Penn State University
https://extension.psu.edu/magnolia-scale
University of Wisconsin
https://hort.extension.wisc.edu/articles/magnolia-scale/
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.
