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I have a healthy Jasmine that is trained against a brick wall. It covers a width of some 3m and reaches to 2.5m tall.

It has suddenly been afflicted by a large aphid infestation, so I was planning to use a winter wash to kill the eggs over the coming winter.

However, I have heard that a winter wash can stain brickwork. Is that true? and if so, is there any mitigation available?

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You could read the information on your winter wash (but probably too generic, so a "it is possible that").

It depends also on the type of bricks (usually they are clay, so never put acid stuffs on them).

Bricks are often porous: you may notice it, that wet brick (rain) are usually much darker. Oil will just attach on them, and it is difficult (and it takes also times), before the colour return normal).

As in the first point, you may notice that most "pesticides" doesn't recommend to be used near artefacts (and often near other vegetables: varieties and species not specifically listed).

You have few choices: try with water (a lot, and stark), racks all leaves regularly. Pruning could also help. If you have similar plants, or other plants with aphids, do winter wash on them. This will reduce the problem. So in addition, you need one of these things:

You could use (in vegetative state) some systematic pesticide: it will enter in the sap, and sap will distribute on all parts. Just a warning: do not burn the leaves. Maybe you should do in several days (so that you have all dose, but given only on easy accessible part of the plant). [Or some biological methods: you may be able to buy ladybugs or other aphid killers]

I saw also some gardener using a paint brush. It may be practical for small plants (or after a heavy pruning).

Sap is also a method. Like oil has some surface tension which may kill eggs, but sap works on aphids also on vegetative state (unlike winter oils). But also in this case you may have problem with bricks (much more seldom). Try on a place where nobody notice it (so usually on bottom part of a wall)

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  • Note that systemic insecticides will enter the flower and kill pollinators. Given that you're growing a jasmine, this could mean quite a few dead bees, hoverflies and maybe butterflies. You'd be better off with beneficials or insecticidal soaps (if that's convenient - depends on the height of the jasmine). – Jurp Nov 27 '20 at 23:26
  • @Jurp: it depends. Many insecticides are specific, so they will kill just some insects, but "not" the pollinators. Unfortunately, for bees, there is an unacceptable 30% or 40% casualties before considering dangerous to bees (and much more to be considered "lethal"). But many non-dangerous are really much less dangerous. In any case: rule #1: always uses specific insecticides/fungicides ("specific": target a small group of insects). – Giacomo Catenazzi Nov 29 '20 at 16:28
  • No, systemics are NOT targeted: any insect that eats the plant, eats the sap, or eats the pollen will die. It's "targeted"only in the sense that it targets herbivorous insects only (as far as I know, carnivorous insects are not hurt if they eat an insect that has ingested a systemic insecticide). Contact insecticides are non-specific, in that they can harm other creatures than insects as well as carnivorous insects like ladybird beetle larvae. Your rule ! 1 is absolutely correct - before applying anything, know what you're trying to kill. – Jurp Nov 29 '20 at 19:06
  • @Jurp: note you mixed "systematic" and "contact" (on your last comment). But I disagree on both. It goes to sap (or just on surface), but some chemistries harm some species and not others. What kills some animals may not kill others. – Giacomo Catenazzi Nov 29 '20 at 19:27
  • Catanazzi - actually, I didn't mix them up - systemic insecticides only affect herbivorous insects, but affect ALL herbivorous insects that eat the plant. Contact insecticides affect ALL insects that the insecticide comes in contact with. IMO, both are unnecessary in most outdoor environments (indoors are different because you have more control on the environment). If you know of scientific information that shows systemics can be targeted to specific herbivorous insects, please post a link to it. – Jurp Nov 30 '20 at 1:25

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