Conspicuous damage seems to be associated with low, overhanging branches and roofs. When shrubs planted away from these it may not occur.

The spoiler for me is not weevils but foliage mildew, since this appeared here (and became ubiquitous) I've gone pretty cool on rhododendrons.

Some rhodo cultivars are higher on their menus than others. Your new one may be the current blue plate special:-)

Tanglefoot is often used for this purpose, as it can effectively slow the access of the adults to the foliage and top growth. But as bboy notes, proximity to wooden structures or other woody plants and low hanging branches may provide alternate means of access. Oddly, in my heavily wooded new garden, all the existing rhodies have rather pristine foliage and since I've not been here long enough to see them bloom, assume they must be on the less favored meal list.

The problem with nematodes is that they only target the larvae. If the adults are not controlled or eliminated as well, they will simply proliferate in future seasons as they continue to lay eggs. I've not seen any evidence to suggest that once applied, populations of beneficial nematodes expand to make future applications unnecessary. Most sources state that routine, yearly applications are necessary to effect any kind of control.

Here is a link that might be useful: root weevils and nematodes

I think the nematodes are not cold climate adapted, and this accounts for the limitations on their use in the north. As on the Rhododendron Society Web Site page linked to above, when they first came out soil temperature was stressed; I think the word was the soil needed to be 50F or above.

If they all die later, during the winter that would explain the need for annual re-application.

I usually spray the nematodes in June it's usually warm enough then. Last winter was very cold for here so that might be the explanation, it's been many a year since our temps have dropped below 0*F. We're having another cold winter so will definitely spray again next spring and the next and.... I'll also use Tanglefoot to trap some of the adults.

Annette

The Rhododendron Society discussion linked to above says (emphasis mine):

"Nematodes do require specific conditions to be effective. A specific temperature range (soil temperature must be above 55 F, 13°C) is required. Because the nematodes are free swimming, the ground must be moist. It is advisable to apply water before and after applying. Applications must be made in accordance with the date listed on the container and application rates must be strictly adhered to. Beneficial nematodes are not found naturally in the soils of most areas, so must be applied yearly. They are only effective against the larvae, and the most beneficial time for application is in the fall. Applications in late summer can only be effective if there are larvae present"

Bboy thanks for bringing this to my attention, I'll give it a try in the fall as well, maybe I can get them coming and going.

Annette

Cleaning out the leaf litter in the fall will go a long way toward limiting the number of root weevils that over winter.

Might also have some effect on foliage mildew. But don't leave the rhododendrons (or any other ornamentals) standing there in bare soil.

Someone gave me some rhododendrons once that had leaves all chewed up by weevils. I cut off all the branches touching the ground and soaked the rootballs in a pond for two days and then planted them. No problems with weevils on those ever since. I drowned them. Unorthodox, but it worked.