West Sussex,
United Kingdom 
Vine weevils
When is the best time to apply vine weevil killer? I didn't do it in the spring and wondered whether it would be effective if applied in July? I haven't seen any weevils but do have two collapsed plants with the roots sheared off.
13 Jul, 2021
Previous question
Assuming you are referring to chemical & not biological control then from memory in autumn
I think this is because the grubs are not hatched until then, plus the insecticide is systemic & don't want it transferred to pollen [flowers should be over] or fruit
Depending on the brand it stays in the compost working over winter, which is the peak root chomping season
No doubt full directions will be on the package or manufactures web site?
13 Jul, 2021