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I brought in my bay laurel (aka sweet bay, laurus nobilis) to clean it, and noticed an infestation of tiny "bug sacks" underneath the leaves, along the veins. What are they? I don't see any actual insects crawling around, (with my bare eyes).

I can get them off the leaf easily by exerting a tiny amount of pressure with a wiping rag. Is there a household product I can use, such as acetic acid, or some concoction of tea tree oil, that would remove them? I wish for them to magically fall off and disappear.

Climate: This plant lives in Vancouver, BC (wikipedia: Climate of Vancouver). It is not hot during the day, and it could not be any rainier. The pot sits on the north side of the building. Sits rarely in direct sunlight, since it is cloudy all the time and a nearby large conifer casts shadows. It stands on a covered patio most of the time

topside underside underside closeup vancouver climate

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You have a scale infestation.

I know I’ll get responses to this blog, that sympathetic gardeners will be recommending me a wide range of products and treatments to control scale insects: rubbing alcohol, insecticidal soap, neem oil, horticultural oil, dancing around a cow’s horn at full moon, etc. But scale insects are sneaky. If even one escapes treatment, the infestation will resume… in six months, nine months, a year.

https://laidbackgardener.blog/tag/scale-insects-on-bay-laurel/

Good luck.

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  • So, I have to burn the house down, burn all my clothes and change my name? That blog article is bleak. Thanks for pointing it out. This specimen has the same symptoms. Like in the blog article, I had noticed the sticky puddles on top of some leaves, and assumed it was simply bay leaf "resin" -- must be a defense mechanism. – init_js Feb 4 '18 at 23:28
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    scale insects can excrete a honeydew substance which can be used by ants which can then farm the scale like they farm aphids. – Graham Chiu Feb 4 '18 at 23:51
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    Ges louise. No you do not have to burn your house down. You have to repot in sterilized potting soil, spray this plant with NEEM (do this in the shower) gently clean the leaves off, spray lightly again. Spray the top of the new soil as well, lightly. Honeydew is a secondary deal...yummy excrement of the scale is loved by bacteria and fungus who eat this stuff and turn the excrement black. No big deal. The fact your plant lives out of doors is how it got scale. It is not a death sentence. Keep an eye on your plant for further infestation. Repotting and periodic spraying will work. – stormy Feb 5 '18 at 6:59
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    While I almost always go the “gentle and organic” route, for scale I have occasionally used systematic insecticides... Not an option if you want to use the leaves in your kitchen, though. And this specimen has a serious infestation. Whatever you decide to use, be prepared to repeat the exercise a few times. Scale is sneaky and for the first few rounds there will almost certainly be a few that survive in some nook or cranny. The bright side: As you are constantly checking for scale, you will most likely take extra good care of the plant. (You might want to keep it away from other plants.) – Stephie Feb 5 '18 at 20:30
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Graham is correct, this is an advanced scale infestation and they are tricky to control. Here are my recommendations:

  • remove all leaves cleanly with knife or sequiturs. Clean with rubbing alcohol after you are done
  • prepare a mixture of 5ml dish soap and one litre of water.
  • get a rag or cloth and soak in the soap and water
  • apply the soap solution on the rag or cloth and crush the scale
  • wait a few minutes and repeat
  • rinse the soap off the plant
  • reduce water and isolate in a higher light area
  • repeat every six days for another three times

This works by reducing the area to be treated and getting the new scale as they hatch.

Another solution which can be done in the spring is put the plant outside where natural predators will eat the scale. You must accustom the plant to the higher outdoor light levels gradually by moving from shade to higher light areas.

As bay laurel is particularly delicious to scale consider putting the plant outside from spring to fall and giving a quick soap and water treatment before bringing it inside in the fall.

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  • "remove all leaves cleanly". all "dead" leaves, all "affected" leaves? Clean "tools" with rubbing alcohol?, clean "work surface"? What if I was to give the whole plant a bath by holding it upside down in water, while supporting the soil. Would that drown them all? – init_js Feb 4 '18 at 23:37
  • Re: predators. The plant has been sitting outside the last couple months of winter already. Do their predators come out in the spring only? Dinner's ready now ;) – init_js Feb 4 '18 at 23:41
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    @init_js. All leaves is every leaf so that there are less sources of scale. Predators include Lady bugs that are probably dormant in winter – kevinsky Feb 4 '18 at 23:53
  • If I were to remove every leaf affected, I would be left with just branches, roots, and one bud. Can't decide which is worse. Thanks for the tip on predation. – init_js Feb 5 '18 at 4:00
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    Hm. Removing all leaves sounds like step 2 could be “dump on your compost pile”. This plant was produced from probably two or three cuttings and is quite young. I doubt it has the energy to grow back, especially as such a bay laurel has usually just one growth spurt in spring and not much happens during the rest of the year. – Stephie Feb 5 '18 at 22:28
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Yes, scale. I have about a 10 ft one and it looked worse and worse for 2 years until I realized it had bad scale problem.I scraped a lot off with my nail, I think that would be the way to handle your small one. I will hit mine with oil spray ( if I can remember this year ) . Baby oil = mineral oil = dormant spray oil ; it all comes out of the same refinery hydrotreater.

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I have used olive oil (extra virgin). It clogs up the scale insects' lungs and they can be nudged off when dead.

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