Basic Scale Biology
There are two types of scale insects; armored and soft scales. Scale insects hatch from eggs and typically develop through 2 nymphal instar growth stages known as “crawlers”. During this “crawler stage” (many cases mid-May through July) the insects are vulnerable to insecticides and other biological enemies. Once the “crawlers” settle on a feeding location and begin to develop waxy or hard outer coverings, the insects are no longer susceptible to most insecticides.
Targeting the “crawler” stage is imperative to successful pest management.
One slight difference between armored and soft scales is how many generations they can have per year; armored (several), soft (typically only 1). Also, once settled armored scales are stationary whereas soft scales can move (albeit slowly). Many scale insect “crawlers” head towards growing vegetative tips, making this location suitable for scouting. Various sticky traps, including double sided tape wrapped around branches are utilized to determine the presence of scale “crawlers”. As noted prior, the presence of “crawlers” should be first visually confirmed if at all possible as pesticide applications made too early are not effective. Programs that utilized cool season dormant/horticultural oils, proper pruning, and the use of summertime contact or systemic insecticides are most successful.(A detailed scale insect fact-sheet is forthcoming!)
Armored and soft scales can be controlled using the same chemicals if targeting “crawlers”.
Growing Degree-days as of 6/10/2020 (Weather station selected for each location. Ex: NJ50 = Upper Deerfield)
Upper Deerfield (NJ50)= 686 GDD50 Howell/Freehold (NJ10) = 536 GDD50 Pequest (NJ58) = 441 GDD50
Scale insects target growing degree-days
(Egg hatch + crawler emergence = scout and treat as needed)
Pine needle scale – (448)
Maskell scale – (470)
Oystershell scale – (486)
Cottony camellia/taxus scale – (520)
Euonymus scale – (522)
European elm scale – (542)
White prunicola (Peach) scale – (594)
Cryptomeria scale – (600-800)
Golden oak scale (680)
Juniper scale – (694)
Hemlock ‘fioriniae’ scale – (300-799)
Spruce bud scale – (700)
Fletcher Scale – (730)
Azalea bark scale – (737)
Oak lecanium scale – (789)
Beech scale – (800)
Japanese maple scale – (829)
Calico scale – (834)
Cottony maple scale – (850)
European fruit lecanium scale – (940 DD)
Summertime scale treatment options
ROTATE between Insecticide Resistance Action Committee (IRAC #)
Format: [IRAC Group #]: Chemical name (Trade names)
- [1A]: Carbaryl (Sevin SL)
- [1B]: Acephate (Orthene, Leptitect, Precise GN)
- [1B]: Chlorpyrifos (Dursban 50W, DuraGuard ME)
- [1B]: Malathion (Malathion 5 EC)
- [3A]: Cyfluthrin (Decathlon)
- [3A]: Bifenthrin (Talstar S Select, Onyx)
- [3A]: lambda-cyhalothrin (Scimitar GC)
- [3A + 4A] Imidacloprid + Bifenthrin (Allectus SC)
- [3A + 4A] Imidaclopird + cyfluthrin (Discuss NG)
- [4A]: Acetamiprid (TriStar 8.5 SL)
- [16]: Buprofezin (Talus 70DF)
- [7C]: Pyriproxifen (Distance IGR)
- Insecticidal soaps (M-Pede)
- Azadirachtin from the Neem plant: (Aza-Direct, Azatin O or XL, Azatrol EC)
Please read the label. The label will provide allowable plant species, use rates, restrictions (phytotoxicity or pollinator concerns), and re-application intervals.
Some useful scale resources: (bare in mind there is variability amongst models and GDD depending on the source, but generally the information will help you make better pest management choices)
- https://www.canr.msu.edu/uploads/files/e2812.pdf
- https://plant-pest-advisory.rutgers.edu/beware-of-the-cryptomeria-scale-hiding-beneath-a-transparent-cover/
- https://www.canr.msu.edu/news/managing_soft_scales_in_conifers#:~:text=Spruce%20bud%20scale%20is%20typically,more%20often%20than%20higher%20branches.&text=Usually%2C%20eggs%20hatch%20and%20tiny,or%20GDD%2C%20base%205).
- http://cues.cfans.umn.edu/old/Web/102CottonyMapleScale.pdf
- https://www.canr.msu.edu/ipm/agriculture/christmas_trees/gdd_of_landscape_insects
- https://plant-pest-advisory.rutgers.edu/beware-of-the-cryptomeria-scale-hiding-beneath-a-transparent-cover/
Southeastern U.S. Pest Control Guide for Nursery Crops and Landscape Plantings: https://content.ces.ncsu.edu/southeastern-us-pest-control-guide-for-nursery-crops-and-landscape-plantings
Rutgers Insect Control Recommendations for Shade Trees and Commercial Nursery Crops: https://njaes.rutgers.edu/pubs/publication.php?pid=E334
Online events and Rutgers Resources:
Ask the Agent (every Wednesday @ 7:00pm): Join: https://go.rutgers.edu/t7wjkit1
NJNLA- Wine Down Wednesdays (every first and third Wednesday @ 7:00pm-8:00pm). Email: Lori Jenssen @ njnla.director@gmail.com
Please take the 2020 Nursery Industry Survey: https://forms.gle/dUjLxaiu6qDQYYsRA
Subscribe to the NJAES YouTube webpage: https://www.youtube.com/user/RutgersNJAES/
RU Sustainable Nursery Production website: https://njaes.rutgers.edu/nursery/
How to use growing degree-day resources: https://plant-pest-advisory.rutgers.edu/using-growing-degree-day-calculators-nursery-pest-and-pathogen-updates-important-resource-links/
NJAES; Plant Diagnostic Lab: https://njaes.rutgers.edu/plant-diagnostic-lab/
NJAES; Soil Testing Lab: https://njaes.rutgers.edu/soil-testing-lab/
Contact: Timothy Waller, Ph.D. at: twaller@njaes.rutgers.edu
