[Eric Vinje]

Hi Shirley –

This is a tricky situation where any pesticidal spray is going to affect both the milkweed weevils and also the monarch butterflies. I think you were on the right path with the pheromones, but there might be some other, better options. I’ve found some articles that suggest gypsy moth traps have been shown to capture a few milkweed stem weevils, however it seems like the weevils were probably there by chance due to the high amount of traps they applied in the study (most pheromone lures are specific to a pest). A more effective control (in terms of cost and eradicating the weevil) would be to apply nematodes directly to the larva in the stems. Mix up a solution of nematodes with water, pull some of it up with garden syringe, and inject a bit into each entrance hole on the stems. Along with this, another preventative option would be to create a barrier between the plant and the ground, such as a plastic mulch. Since the weevils drop from the plant to pupate in the ground, this would block them from being able to do that.

Hope it helps!