BLACK FLY

Its the actual soap that wins, preferably without perfume. Can recommend carbolic but where can you find any ?

 

That's very interesting.

I don't thing squirting blackfly with water is likely to do very much, after an experiment. In this weather they might even enjoy it!

What about this stuff:

REDBUOY Carbolic Household Soap 3x Twin Packs each 2x130g Bars | eBay

Hope that comes out OK. It seems to be "proper" carbolic soap (Wright's isn't, as I discovered a coiuple of years ago). There are various vendors of this soap, not limited to eBay. EDIT: (Barnitts, an online shop) "Please be aware that this soap does not contain the ingredient Carbolic. The ingredients are as follows

Sodium Palmate, Sodium Palm Kernelate, Aqua, m-Cresol, p-Cresol, Parfum, Glycerin, Sodium Chloride, Tetrasodium EDTA, Tetrasodium Editronate, Linalool, Limonene, CI11680, Ci12490"

EDIT: There's also this, although it contains "perfume":

Blue Power Carbolic Soap 4.4oz is a product of Jamaica and has been traditionally used in most households for personal hygiene. In the past it was also used extensively in hospitals, and other places where hygiene was at the top of the list.

Sodium palmate/palm kernalate, water, glycerine, cresylic acid, carbolic acid, fragrance, sodium dtpa, colour red LJ3010.


What do you do with it? Grate the soap up and dissolve it in water? Any idea of quantities?

 

I understand that the effect required is to' unstick' the aphid larvae without damaging the plant tissue, so that a flood of water carries them away. This is necessary otherwise rain would do the job. Additional modern ingredients have uncertain effects and I choose to avoid them.
All that is necessary is to wash your hands with a true soap (of course they dont need it!) and retain the washing water (do it in a bucket). This can be sprayed on to the aphid larvae and subsequently rinsed. Work from top to base so as to clear the plant.
If the 'victim' is a brassica, (with wooly grey aphis for example) then the addition of sodium chloride (table salt) @ 10 grams/litre can be effective. You may be needing to repeat 'upon demand' as it is difficult to be 100%
The salt treatment can also be used on caterpillars on brassicas, especially when first hatched.

 

@infradig
I am somewhat confused by your comment

Blackfly and blackfly aphids are, to the best of my knowledge, exactly the same thing.

 

Squirting with water has a mechanical effect, it knocks them off the plant.

 

Given that tomato are not a frequent host to black fly aphid, I merely wished to point out to the OP that the depicted insect need not in fact be such.
/www.google.com/search?q=Black+flying+species+of+insect&tbm=isch&ved=2ahUKEwjjgquSmsX_AhXkrycCHQVpCc8Q2-cCegQIABAA&oq=Black+flying+species+of+insect&gs_lcp=CgNpbWcQAzoHCAAQigUQQzoHCAAQGBCABDoFCAAQgAQ6BggAEAUQHjoGCAAQCBAeULMXWNVkYKVsaABwAHgAgAG0AYgB5hCSAQQxNy41mAEAoAEBqgELZ3dzLXdpei1pbWfAAQE&sclient=img&ei=VfqKZKOEHeTfnsEPhdKl-Aw&bih=564&biw=1252&client=firefox-b-d

 

Broadbeans pinch the tops out, a jet of water knocks them off and they don't climb back quickly, squishing between fingers can be satisfying.
The action of soap on insects is to reduce or remove the waxy coating they have on the outside. The insect is then no longer waterproof and lose water through the cuticle.

 

A "general" reply: I note that the RHS dn't mention spraying with water to wash off these bugs (Blackfly (Black Bean Aphid)), or using soapy water, at all, but do mention either squishing them (which, with a large infestation, I think would be time consuming, messy, and damage the plant), or using pesticides.

Anyway, I ordered some bars of Blue Power carbolic soap, for an experiment (first on one plant) and also just to use as soap.

 

There is a reason for neither soapy water or plain water being mentioned, neither of these have been licenced as pesticides for the control of blackfly and it would, technically, be illegal for the RHS to recommend their use.
Note many contact insecticides contain soap or soap like compounds that remove the waxy coating.
Squishing the blackfly doesn't really damage the plants just run finger and thumb up the stem.
Pinching the top few inches out works well and if you do this before blackfly arrive then they can be cooked, few minutes in boiling water, and eaten.