Death to scale bugs - help me brew up some organic death spray to save my citrus trees

r ranson wrote:Any other solutions?

I've tried the lot and um, the scale bugs are winning.  

I have two in-ground satsuma mandarin trees in my greenhouse and have been fighting scale for about 4 years now.  Up till recently, I've been spraying them with an alcohol/water/horticultural oil mix a couple of times a year, but just have not been seeing good results.  

Last weekend I decided to declare war.  I brought out the spray, but also a good pair of glasses (to clearly see the branches/leaves up close) and a toothbrush.  I sat by each tree and painstakingly sprayed every single branch and leaf, while scrubbing the visible scale off every leaf, branch, junction between leaves/branches/trunk with the toothbrush.  I cut off every dead branch or overly damaged bits of my trees and threw them outside the greenhouse.

My plan is to go back every month or so and examine the trees up close for any sign of activity.  I think in the past I was assuming just spraying the trees would get rid of the scale, but I think the physical removal of every insect I can see will make the spray much more effective.

This past year, I just haven't had the mental or physical energy to baby my two lemon trees that had scale. Our front porch is fairly sheltered, and the plants are too young to produce fruit, so I decided just to leave them outside.

That was working fine until it snowed... which was then followed a couple of weeks later by below freezing weather as cold as -7C. The smaller plant died, but the bigger one not only survived, it's got signs of new shoots in the last week.

The scale disappeared over the winter. Yesterday, I spotted an ant on the plant, and sure enough, today I could see several small scale bugs which I scraped off.

I think I need to pay much more attention to the sugar ant/scale connection. I'm thinking of mixing diatomaceous earth with just enough water than I can paint it on the stem. When it dries, will it still have ant deterring characteristics? I do also have tanglefoot, but the stem is only about the thickness of my ring finger, so trying to protect the stem, while not squeezing it too much, while getting the tanglefoot spread evenly, all seems like a struggle. For a larger tree, I would happily try it.

Ants transport scale bugs to new plants to farm them.  So, oddly, putting citrus plants outside in summer both reduces the severity of infestations (predators? wind? rain? IDK) and exposes them to new infestations from ants (or even wind from what I've read.)  Male scale bugs can fly, so that could contribute to their spread as well.

Cold weather does seem to help with any infestations, so my mandarin orange tree, which can handle freezing temps on occasion, has the least infestation, and over this past winter did not develop any visible scale or spider mites for the first time, after I left it outside later into the fall last year and put it indoors away from my other citrus trees that had to come in earlier.  My poor little meyer lemon, however, is dying back heavily from scale and it's still too cold at night to put it outside.  Spray never gets everything, although it helps, and I'm always trying not to get spray on my walls so probably don't get it onto every surface of the plant.  If anyone comes up with a "better mousetrap," I'll look forward to trying it.  Maybe something with oil to smother them?  

My rubbing alcohol and soap scrub removed the scale, but killed the branches.  It's taking them a while to grow new ones.

The trees are all outside now, but the ants are depositing scale as quickly as they can.  sigh.