Yellowing lower leaves are most likely the natural shedding of the oldest leaves. Notched edges on the leaves are almost certainly weevil damage. I don't think it's possible to grow rhododendrons without encountering these pests. One way to confirm their presence is to check the plants at night when the adult weevils feed. While there are pesticides available for weevils (all of them pretty toxic stuff), control is not easy and complete eradication is impossible. Unless the investation is extremely severe, the damage is more unsightly than a lethal threat to the plant. Rhododendrons with thin leaves (like Lee's Dark Purple) are more prone to damage than ones with thick indumented leaves such as r. yakusimanum and its many hybrid offspring.

Thanks for the reply, mainegrower. I think I will just keep an eye on them for now and see what happens. The weevil damage doesn't look really bad so far, but the yellowing looks scary to me.

I have been reading about using beneficial nematodes on weevils, any thoughts on this?

Hello, tigerlily_oh. The night crawling {{gwi:396053}} usually does most of the {{gwi:396055}} that you have noticed. They feed off the leaves but it is the {{gwi:396057}} the ones you have to worry about. They feed on the plant's roots and can kill the plant.

At first, the adults feed on the leaves. Then they leave their eggs in the soil; the larvae grow in 2-3 weeks; the plant stops growing, the foliage often yellows and may dry out as the larvae begin to feed on the roots.

There are no 100% effective larval drenches that will kill the young although some people recommend trying beneficial nematodes. To control the adult weevil, several chemicals can help.

It is important to take action when you still have time and most of the plant is still alive. You want to try and kill the adults before egg laying happens en masse. A small infestation can be ignored but you have to monitor the plant for signs of unusual yellowing. That indicates that the larvae have been born and are feeding off the roots.

To control the adult population, plants should be sprayed thoroughly with insecticides containing acephate, bendiocarb, chlorpyrifos or fluvalinate around mid-June (if infested in the prev year) or when adult feeding damage (notching) is first discovered. Follow directions; a second aplication may be needed.

To control the larvae population, carefully remove them by hand (watch out for the tiny plant roots though) or apply beneficial nematodes against the larvae. The entomopathogenic nematodes, Steinernema and Heterorhabditis spp., have been effective for controlling larvae in pots and may work here. For a list of retail suppliers, click here.

Good luck,
Luis