Rhododendrons: How can I remove weevils before replanting?

One of our garden club members has a fairly healthy looking rhodo which has been growing in a barrel for a while.* He wants to dig it out and give it to someone else for her garden, however, the lower leaves have all been eaten by what looks to me like root weevil.* Should he wash all the soil off the roots before replanting it to get rid of any weevils/larvae etc.?* Or should he just use Tanglefoot on the stem as I think the roots could so easily be damaged by washing the soil off. Or nematodes (from where or from whom)?
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Any other suggestions?

 

if you are certain of the culprit being weevil, nematodes is probably the best idea. make sure to check soil temp for appropriate species application.

 

Wash the roots. Look for grubs up under the main stem.

 

Louis--the nematodes are a bit pricey, and need at least 10C soil temps to do their work. It might be a waste to do them now, as the nematodes might not be able to thrive in the marginal temps from now till sometime in spring.

I think it was in these forums someone mentioned the trick used by a European grower. He submerges the root system totally in water for 24 hours, drowning the weevils. Perhaps you could even plug the drain holes where it is growing now and fill that barrel to overflowing with water. And don't leave the water any longer than that or roots could suffer/drown.

 

That is a good idea! I recently found out that Heuchera are prone to root weevils. I wonder if that could be a cause for their less than vigorous performance sometimes. Drowning would work for plants in a container, but what about in the ground? Has anybody heard of using a hot water drench? I realize it would be risky.

 

If it is hot enough to kill the weevils, would have to be very hot, then probably hot enough to kill the plant. Understand ants can stay alive underwater for weeks (yea I seen the Orkin man LOL) so how long can weevils stay alive underwater for? Preditory Nematodes are said to kill vine weevil but not sure how effective they are against root weevils, but migh be worth a try.

 

Fourd--I have similar questions about trying to drown most soil organisms, certainly earthworms are able to live for weeks in waterlogged soils.

I wouldn't have thought of the drowning thing except someone mentioned the nurseryman who was doing it with apparent success. Personally I use the nematodes here, as we have tons of weevil damage otherwise and a large area to cover.

My nematode supplier indicates they will attack most if not all the weevil species, as the various weevils all have a root munching larval form that the nematodes can attack. Trick is knowing when to apply the nematodes...the gov't guide here in BC suggests around Labor Day for treating conifer seedlings, so that is an indication for my area. Weevils have to be in larval stage, and temps above 10C, and soil moist...and nematodes cost a fair bit so want to make best use of the application...

 

Since rhododendrons are prone to rotting of the roots by water molds, generally require a highly aerated rooting medium I wonder about leaving one sitting in water. I would try to expose the weevils via washing with clean water, pick them all off and be done with it. I wouldn't worry about barerooting a rhododendron, as long as it was kept moist.

http://www.puyallup.wsu.edu/~Linda Chalker-Scott/Horticultural Myths_files/Myths/Fragile roots.pdf

 

I think I may have brought some weevils up on some munched up rhodies- I thought maybe slugs ate the leaves. Will check the roots...

 

First, while Rhodos do indeed need well aerated roots, they can survive a day or so with their roots submerged. I have a couple of Rhodos that are planted in an area that gets wet enough to have standing surface water once in awhile when there is a heavy rain, and the roots get submerged for a day or more, but they have never shown any effect from that treatment (never checked to see if they have less weevil signs, come to think of it).

I have also restored plants that were dessicated, having been pulled from the ground and left with dry roots, looking pretty much dead, by simply tossing them into the fish pnd for a day or so and then planting them.

I have to wonder if weevil isn't more of a concern for nurserymen seeking nice looking saleable plants, than for people with normal gardens. Personally, I tend to ignore weevil munchings, because I'd go broke and get neurotic trying to treat it in a large garden, and it tends to go away anyway as the plants get better established and happy.

I know of one lady that probably shouldn't garden - she spends her entire spring and summer worrying about the weevils and obsessively deadheading her Rhodos, almost to the point of hiring a kid to climb a ladder to deadhead the ones she can't reach, except she'd be too worried about the kid falling off the ladder.......gardening is supposed to have a calming effect on people, isn't it?