|notches on rhody leaves|
The cause and culprit in this case are adult root weevils (snout beetles). There are many species of root weevil (Curculionidae) but all exhibit the same general life cycle. Worm-like larvae feed on plant roots for most of the year, adult beetles (weevils) emerge from the soil in spring or summer, feed (notch) on leaves of the host plant, lay eggs then die. The real damage therefore is to the root system of affected plants but it is the leaf notching that catches the attention of gardeners.
|black vine weevil adult|
Fortunately leaf notches are a perfect way to time when adult weevils are starting to emerge and feed. As soon as you see new notches appear in spring/early summer start your control program!
Leaves can be treated with a variety of garden insecticides to stop weevils from feeding. Neem oil insecticide is a low toxicity choice that works well.