[Anton]

Help please. I have just planted some leeks and as I know the leek moth lays  its eggs in March and April (first cycle), when should I give them a spray with a rhodedendrum-based insecticide, whose name escapes me. And how many times. In autum I think I spray them twice/three times!

[New shoot]

I don’t know the insecticide you are referring to.  The only plant based one I am familiar with is pyrethrum, but I assume the same info would apply.  For contact insecticides like these, they don’t penetrate the plant so have to be applied regularly.  Rain washes them off.

I don’t know if pyrethrum or the insecticide you are using are effective against leaf moth tbh.  I rely on very fine insect barrier netting.

[Anton]

Thanks for your reply. I found the box: Bio-Pyretrex.
 I tried the netting trick but despite me being extremely careful they vermin still managed to get in and ravage the crop. I was going to try some of those traps that imitate the odour of the female moth to attract the males but the fellow in the gardning shop recommended Bio-Pyretrex and this worked a treat. I think I applied it every second week in September and October but I am not sure I applied in in April (which was when I planted some last year).