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 of 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 presence of holes in the scale covers indicating parasitic wasp activity.
Natural enemies include:
- lady beetles, Chilocorus spp.
- Rhizobius-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 emergence of the vulnerable crawlers. Ants, fond of honeydew, will fight off scale natural enemies to protect the source.
- 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.
- azadiractin (Azahar)-Some formulations are OMRI-listed for organic use.
- 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.
- canola oil/pyrethrin (E.B. Stone, Earth-tone, Worryfree)-Some formulations are OMRI-listed for organic use.
- chlorpyrifos (Quali-Pro Chlorpyrifos) at 1 lb ai/100 gal. REI 24 hr. Restricted use pesticide.
- clothianidin (Arena 0.25G) at 1 to 1.5 oz ai/100 gal. REI 12 hr. Soft scale.
- clarified hydrophobic extract of neem oil (Triact 70)
- cyantraniliprole (Mainspring) at 0.013 to 0.1 lb ai/100 gal. REI 4 hr.
- cyfluthrin (Decathlon) at 1.9 oz/100 gal. REI 12 hr.
- cyfluthrin/imidacloprid (Discus N/G) at 0.063 lb ai/100 gal foliar; 0.009 to 0.014 lb ai/1,000 ft soil. REI 12 hr.
- 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.
- 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.
- garlic oil/powder (Allityn)-Some formulations are OMRI-listed for organic use.
- 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.
- mineral oil/petroleum distillate (Biocover LS)
- oil of rosemary/peppermint (Ecotec for WA only)-Some formulations are OMRI-listed for organic use.
- pyrethrum/piperonyl butoxide
- 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.
- soybean oil (Golden Pest Spray)-Some formulations are OMRI-listed for organic use.
- spirotetramat (Konotos) at 0.027 to 0.053 lb ai /100 gal. REI 24 hr. For crawlers.
- thyme oil/phenethyl propionate (EcoVia WD) at 1 to 4 oz product per 1,000 sq ft. FIFRA Section 25b exempt product.
- tolfenpyrad (Hachi-Hachi) at 0.14 to 0.33 lb ai /100 gal. REI 12 hr.