Lime sulfur works (if you can find it for sale anywhere), as do any of the copper-based sprays (which are easier to get nowadays) and also garden oils like Volck oil or any of the emulsified canola oils you can buy at a garden center (not the kitchen kind). Anything with that "kill on contact" and/or smother everything will work for this purpose.

The label is the law in California, so DO read it and do what they say in terms of application rates.

You should not use Volck if the growth has started coming out,

Thanks kstrong and dan_keil_cr.