I wouldn't dream of applying any chemicals to potential food. You may
as well spoon it in and see what happens!
The original poster got it right with mesh. If mesh netting is used it
prevents the Large White and Small White butterflies form laying their
eggs. The former produce the speckled yellow, green and black
caterpillars, the latter the green ones. And if there isn't enough
mesh, go out and get some more.