Need more info - where are these 'beans of cotton' - on woody stems? On leaves? On flowers? A photograph of them would be very useful.

ditto

......on woody stems......I'm sorry, my cell phone is not working, so I can't take a photo. Thanks............

Also, Tania, what kinds of plants are involved?

Sounds like one of the scale insects to me - which one depends on the host plant, but as its on the woody parts, what I'd do is get a disposable cloth or three, moisten it very lightly (don't soak it) with methylated spirits, and rub it over the affected wood, scraping off the scale as I go. Which is why you need more than one cloth... they get really mucky. Cannot be used on leaves and green parts though, and only works on reasonably smooth bark.

If by "garden", you mean vegetable garden, then things get more difficult, since that is likely to be all green stems and leaves, and the most effective sprays on mealybugs and scale--the likeliest candidates--are nearly too toxic to use on edibles.