Pest description and crop There are two types of scale insects commonly encountered in greenhouses: hard scale and soft scale. Hard scale insects tend to be fairly small in size and lie flatter against the stems than do soft scale insects. Soft scale insects are often very rounded and will also produce honeydew with their associated black sooty mold. Scale insects may have only one or multiple generations per year. Scale insects often come into a greenhouse on propagation material. This example shows the importance of inspections and, sometimes, quarantine any new plant material brought into the greenhouse. Early infestations can often be rogued or pruned out.
Biology and life history Most scale insects are female. Mature females are wingless and often secrete a hard shell-like covering for protection. The males are rare, small, non-feeding, and short-lived but look more like other insects as they have wings. With a few notable exceptions, the first immature stage, or the first "instar" females, are generally the only stage that disperses on plant material. All other stages remain attached to the plant surface, sessile. Females lay eggs or crawlers under their secreted scale covering or in a cavity under their bodies.
Scouting and thresholds Look for scale insects along stems and leaf undersides. Double-sided sticky tape can be used to check for emerging scale crawlers.
Check for the presence of holes in the scale covers indicating parasitic wasp activity.
Natural enemies include:
- lady beetles, Chilocorus spp.
- Rhizobius-A soft scale predator.
Mealybug and scale pests are best controlled at the "crawler" stage: the immature, active stage when the insects are most sensitive to insecticides. Spray applications should be timed to coincide with the emergence of vulnerable crawlers. Ants, fond of honeydew, will fight off scale natural enemies to protect the source.
- abamectin (Aracinate) at 5 mL per 2 inches of cumulative trunk diameter at 4.5 ft above ground level.
- acephate (Orthene TR) at 0.024 lb ai/1,000 sq ft broadcast (0.6 oz). REI 24 hr.
- acetamiprid (Tristar 30SG) at 0.5 to 0.1 lb ai/100 gal (2.7 to 5.3 oz). REI 12 hr.
- afidopyropen (Ventigra) at 4.8 to 7.0 fl oz per 100 gal.
- ammonium nonanoate (AXXE Broad Spectrum)-Spray directly on the soil, the solution varies by level of insect pressure (low 6-8%, medium 8-10%, high 10-13%).
- azadiractin (Azahar)-Some formulations are OMRI-listed for organic use.
- beta-cyfluthrin (Tempo Ultra GC) at 45 to 160 mL (1.5 to 5.4 fl oz) per 100 gal water.
- bifenthrin (Talstar) at 0.168 to 0.335 lb ai/1,000 sq ft. REI 12 hr. Restricted use pesticide.
- buprofezin (Talus 70DF) at 0.88 lb ai/A. REI 12 hr.
- Burkholderia spp. (Venerate)-OMRI-listed
- canola oil/pyrethrin --Some formulations are OMRI-listed for organic use.
- carbaryl (Sevin SL) at 1 quart per acre or per 100 gal (0.75 fl oz per 1,000 sq ft).
- Chromobacterium (Grandevo)-Application rates based on host plant.
- cinnamaldehyde (Seican)-Variable rates for the first appearance, common and high pressure.
- cinnamon oil (Cinnerate) at 13 to 64 fl oz/100 gal, 50 to 210 gal/A.
- clothianidin (Arena 0.25G) at 1 to 1.5 oz ai/100 gal. REI 12 hr. Soft scale.
- cyantraniliprole (Mainspring GNL) at 0.013 to 0.1 lb ai/100 gal. REI 4 hr.
- cottonseed oil, peppermint oil, geraniol, rosemary oil (Furious) at 22 to 33 fl oz/A or 3 fl oz/gal for 1,000 sq ft. WA only.
- cyantraniliprole (Mainspring) 2 to 8 fl oz per 100 gal (0.6 to 2.4 ml per gal). Reapply on a 7- to 14-day interval.
- cyclaniliprole (Sarisa) at 16.4 to 27 fl oz/100 gal.
- cyfluthrin (Decathlon 20WP) at 1.9 oz/100 gal. REI 12 hr.
- cyfluthrin/imidacloprid (Discus L) at 0.063 lb ai/100 gal foliar; 0.009 to 0.014 lb ai/1,000 ft soil. REI 12 hr.
- cyhalothrin (Scion) at 1.3 to 4.4 fl oz per 100 gal -or- 39-132 ml per 100 gal
- deltamethrin (D-Fense SC)-Apply as a coarse spray at 0.25 to 1.5 fl oz for 1,000 sq ft.
- diazinon (Diazinon AG600 WBC) at 0.5 fl oz per 3 gal or 12.75 fl oz per 100 gal water.
- dicrotophos (Inject-a-cide) for obscure scale on Oak-Inject when crawlers appear.
- dimethoate (Dimethoate 400)-Variable application based on host plant.
- dinotefuran (Safari 20SG) at 0.1 to 0.2 lb ai/1,000 ft sq; 0.05 to 0.1 lb ai/100 gal. REI 12 hr.
- emamectin (TREE-age) target scale on buds and leaf, rate based on DBH.
- esfenvalerate (Onslaught) broadcast or foliar spray at 0.1 to 1.0 fl oz/gal for 1,000 sq ft.
- fenpropathrin (Valent Tame 2)-For San Jose scale crawlers. Must mix with Tame 2.4 EC.
- flonicamid (Aria) at 0.067 to 0.134 lb ai/100 gal. REI 12 hr.
- flupyradifurone (Altus) at 10.5 to 14 fl oz/A. REI 4 hr.
- geraniol, peppermint and rosemary oil (Keyplex Ecotrol) at 16 to 48 fl oz/100 gal; spray at first appearance, every 5-7 days.
- imidacloprid (Marathon II) at 0.027 oz ai /100 gal foliar. REI 12 hr. Drench and irrigation permitted.
- lambda-cyhalothrin (Scimitar GC) at 0.023 to 0.043 lb ai /100 gal. REI 24 hr.
- malathion (malathion 8)-Rate based on scale species and host plant mineral oil/petroleum distillate (Biocover LS).
- mineral oil, petroleum distillate (Wil-Gro) at 1 to 2 gal per 100 gal water.
- naled (Dibrom 8) emulsive insecticide
- neem (Nimbiosys)- 1 to 2 pints/A at 0.5% concentration.
- oxydemeton (Harpoon)
- peppermint oil/rosemary oil (Brandt Ecotec for WA only)-Some formulations are OMRI-listed for organic use.
- pyrethrins/piperonyl butoxide
- phosphine (Eco2Fume) fumigant
- piperonyl butoxide, pyrethrins (Stryker, Pyrenone Crop Spray, Pyronyl Crop Spray)-Various application rates.
- pyrethrins (Lynx EC 1.4) at 16 to 64 fl oz per acre in sufficient water for even coverage, minimum 5 gal.
- pyriproxifen (Distance) at 0.054 to 0.081 lb ai/100 gal (8 to 12 fl oz) foliar. REI 12 hr.
- s-kinoprene (Enstar AQ) at 0.012 to 0.024 lb ai/10,000 sq ft. REI 4 hr. soft scale.
- sodium borate (Prev-Am)-Minimum 20 gal/A.
- soybean oil (Golden Pest Spray)-Some formulations are OMRI-listed for organic use.
- spinetoram (XXPire) at 7.0 oz /A (0.088 lb ai/A)
- spirotetramat (Konotos) at 0.027 to 0.053 lb ai /100 gal. REI 24 hr. For crawlers.
- thiamethoxam (Flagship 25W) at 4 to 8.5 oz/100 gal or 8 to 17 oz/A.
- tolfenpyrad (Hachi-Hachi) at 0.14 to 0.33 lb ai/100 gal. REI 12 hr.