My rhodies are being devastated by root weevils. They have stripped many of the branches clean of their vegetation, and have destroyed ~50% of the remaining leaves. My rhodies look like they will require years to recover, if they ever do.
If I replace them with resistant varieties or plants that are not susceptible to these pests, will this eliminate the weevils?
Root weevils are the most common pest attacking Rhododendrons in the Pacific Northwest so they can only be temporarily eliminated from any garden. If the environment is right and their food source returns, so will the root weevils.
If you want to keep your current Rhododendrons, the weevils can be controlled if you’re diligent (forever!?). An article by Caroline Cox in the summer 2005 issue of the Journal of Pesticide Reform discusses their control. However, it sounds as if you’re willing to remove them and start fresh. Some of the most susceptible (host plants) are Rhododendron and Azalea, Heather, Salal, Manzanita and Kinnikinnick, Pieris, Maples, Viburnum, most Conifers, Astilbe, Cyclamen, Helleborus, Hosta and Primrose.
(Source: Root Weevils in the Nursery and Landscape; Identification and Control, by J. DeAngelis and G. Garth, EC 1485, Oregon State University Extension Service).
The extension bulletin from the Washington State University Extension website has an excellent list of resistant Rhododendron varieties.
Do you have a recommendation for a particularly shade tolerant rhodie? I have dappled shade, but also some areas of fairly deep shade. I’m in the Portland, OR area.
Generally speaking, rhododendrons are tolerant of shade, but need some light if they are to produce flowers. According to Rhododendrons in America by Ted Van Veen (Binford & Mort, 1969), “the larger the leaf, the more shade required … In the Pacific Northwest … most varieties look their best if they have about one-third shade when the sun is warm.”
Dappled shade should be fine for most rhododendrons, but deep shade might mean that you end up with a non-flowering shrub. Look for large-leaved species or hybrids. These are sometimes referred to as elepidotes (generally, this term refers to hybrids with large leaves and flowers that grow in relatively large clusters).
Below are just a few examples of the hundreds of species and hybrids available. (Images and information from Oregon State University are included)
R. catawbiense
R. macrophyllum
Marjatta hybrids
Here is a list of Proven Performers for Oregon, from the American Rhododendron Society:
(These are the recommended large-leaved cultivars from the Portland Chapter:)
- ‘Blue Peter’
- ‘Cynthia’
- ‘Lem’s Cameo’
- ‘Mardi Gras’
- ‘Mrs Furnival’
- ‘Odee Wright’
- ‘Taurus’
- ‘The Hon. Jean Marie de Montague’
- ‘Unique’
Aside from ‘Christmas Cheer,’ are there types of Rhododendrons that have winter flowers and flourish here? I am imagining planting a couple in an island beneath some hybrid elm trees, so they would be in part shade. I have plenty of irrigation, and there is a slight slope to the location.
Another variety which is early to bloom is ‘Nobleanum.’ American Rhododendron Society’s blog has a post by a Pacific Northwest author who lists several others:
- ‘Bo Peep’
- ‘Seta’
- ‘Snow Lady’
- ‘Cilpinense’
- R. mucronulatum ‘Cornell Pink’
- R. dauricum
- R. moupinense
- R. strigillosum
One can also search the American Rhododendron Society site for varieties of Rhododendron which meet various criteria, including bloom time.
Meerkerk Gardens on Whidbey Island lists rhododendrons by month of bloom.
The Rhododendron Species Botanical Garden might be another good resource. They mention that they have just a few species which flower early.