jon frohmaier wrote:
would like to try the washing up trick, how much do you use in a
sprayer?



:-))
Depends how big the sprayer is.
Or whether you are in a hard or soft water area.
Seriously, there is no hard and fast rule. Its trial and error.
Use enough to produce a foamy spray. But the marker (toxic?????) foam
is the byproduct.
You just need enough to allow the water to thoroughly wet the plant.
The same trick works on all waxy leaved plants. Ivy for example.

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ned