black vine weevil active on rhodies

Marie Tulin

10 months ago

Now that isotox is off the market what can we use to stop black vine weevils damaging rhodies?

The critters are really doing a number on this broad leaved evergreen.

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Comments (3)

gardengal48 (PNW Z8/9)
9 months ago
last modified: 9 months ago
You are not going to like my comments.......I don't suggest doing much, if anything.😕

The PNW is rhododendron country - they are in almost every garden and commercial planting, this is home to the Rhododendron Species Foundation and Botanical Garden and it is the state 'flower' of Washington. And weevils - several different species - are one of the few problematic issues encountered here with rhodies. But because these insects are so prevalent - they feed on numerous native plant species as well - they are almost impossible to control.

One option is to replace bothered plants with those that are resistant to weevil predation. Not all rhododendron species and cultivars are equally appealing to the weevils and numerous popular selections have proven to be relatively weevil resistant - any with very fuzzy leaves (like the yakushimanum hybrids), the PJM group choices, Sappho, Dora Amateis, Odee Wright, Cream Crest and Oceanlake for starters. I used to suggest to my clients to use the 10 foot rule - if you stand 10 feet away from the rhody in question and the weevil damage is barely visible, ignore.. If in a very visible position, consider removal and replacement.

The weevil damage is almost entirely cosmetic. Weevil larvae rarely bother the roots of established rhodies (although they can be an issue with a few other popular plants). Notches on the leaves are not going to cause any serious issues.

If you really want to control these insects, you need a multi-pronged approach.
- 1) Use Tanglefoot or other sticky tape around the base of the plant to prevent the night active weevils from climbing up to feed. This will only work if the plant in question cannot be accessed from another adjacent plant or structure (side of house, fence, deck, etc.).
- 2) Spray with a product containing acephate (Orthene). Acephate is an organophosphate so never my first choice for treatment.
- And finally 3) apply beneficial nematodes to control the weevil larvae. The larvae must be controlled if you have any hope to kill the adults as well, otherwise just more adults will appear.
This article published by the American Rhododendron Society may help: Root Weevils - Troublesome Rhododendron Pests
davidrt28 (zone 7)
9 months ago
Gardengal answered this same question for me years ago. They suddenly were attacking my 'Vulcan'. I used approach #3, buying the nematodes from Arbico Organics. Not cheap, but I never had the problem again. Maybe a bite here or there, but gone was the seriously chewed up look.
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There are two weevils that attack rhododendrons and azaleas: Black Vine Weevil or Strawberry Root Weevil They create two entirely different situations: Adult weevils feed on the leaves at night. Leaves chewed on edges is a symptom of the Black Vine Weevil and Strawberry Root Weevil, 1/4"long black beetles. They are nocturnal feeders and can be found at night with a flashlight for identification. Foliar sprays are very effective at controlling adult weevils when leaf notching starts. Foliar sprays of Orthene should be sprayed at about three week intervals from about May to October, depending on the weather, until no adults emerge. Since weevils feed at night, you can hand pick adult weevils at night using a flashlight. Since weevils spend the daytime in the soil and come out at night to feed, you can paint the trunk with Tanglefoot to stop them, but make sure no branches are touching the ground. Foliar sprays are very effective at controlling adult weevils when leaf notching starts. Foliar sprays must be repeated until no adults emerge. The major damage is caused by weevil larvae which girdle the roots and kill the plant. Prior to killing the plant the plant shows signs of chlorosis (yellowing of a leaf between dark green veins.) Larvicidal drenches may be used to kill them but are of limited effectiveness. A more effective approach is to use nematodes. They are very effective against weevils when applied in the fall to control the larvae. While this approach is promising, it has limitations in that the beneficial nematodes are very sensitive to temperature and moisture extremes and will not live over winter. If applied to soil that is too cold, too wet, too dry or too hot, they will die and provide no control. Best control is achieved by using both chemical and nematode methods with proper timing.
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In the proper situation, a healthy azalea or rhododendron is relatively carefree. About the only insects that attacks rhododendrons and azaleas are weevils and lace bugs. Lace bugs attacks rhododendrons that are planted in full sun and are best held at bay by moving affected plants into the shade. The weevils come up at night and eat the edges of leaves. They seldom hurt the plant while eating leaves but the larvae can girdle the roots and kill them. It is best combated with a nematode that keeps it in check. WEEVILS: Leaves chewed on edges is a symptom of chewing insects. Most are nocturnal feeders and can be found at night with a flashlight. The most prominent chewing insects on rhododendrons and azaleas are the Black Vine Weevil and Strawberry Root Weevil, 1/4"long black beetles. Feeding is done at night. Specimens may be collected at night for identification. The major damage is caused by weevil larvae which girdle the roots and kill the plant. Larvicidal drenches may be used to kill them but are of limited effectiveness. A more effective approach is to use nematodes. They are very effective against weevils when applied in the fall to control the larvae. While this approach is promising, it has limitations in that the beneficial nematodes are very sensitive to temperature and moisture extremes and will not live over winter. If applied to soil that is too cold, too wet, too dry or too hot, they will die and provide no control. Best control is achieved by using both chemical and nematode methods with proper timing. Foliar sprays are very effective at controlling adult weevils when leaf notching starts. Foliar sprays of Orthene should be sprayed at about three week intervals from about May to October, depending on the weather, until no adults emerge. Since weevils feed at night, you can hand pick adult weevils at night using a flashlight. Since weevils spend the daytime in the soil and come out at night to feed, you can paint the trunk with Tanglefoot to stop them, but make sure no branches are touching the ground. LACE BUGS: Whitish specks on the upper surface of leaves and dark spots varnish-like on the bottom are symptoms of rhododendron lace bugs, small insects with transparent wings on under-surface of leaves.. They are more prevalent on certain varieties and on plants grown in sunny areas. When damage first appears, it may be controlled by any of a number of contact insecticides such as Malathion or Orthene. Care must be taken to spray the lower surfaces of the leaves where the lace bugs live. Moving a plant to an area with more shade may alleviate the problem. Here is a link that might be useful: How to care for rhododendrons and azaleas.
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Steve- I call them "notch bugs". The adult weevil eats notches in camelias, rhodys , aspidistra, lirope and everything else I like. These plants are evergreen around here, and probably for the OP, so the damage remains for years. The larvae eat the roots and crowns of plants, especially strawberries. Probably more of a problem in areas that don't have hard freezes that penetrate several feet down into the soil. We might have perfect weather, but that also brings some special bugs. ;-) You guys don't have to worry about soil termites either. Beneficial nematodes need the soil temp to be over 50 (from what I've heard locally). In the ground they should last a couple years or so, or until they no longer have grubs to eat. I doubt ammonia would do anything to the grubs w/o totally soaking the soil and likely killing/harming the plants. Where I don't use nematodes, I go for the chemicals. Bayer. -Babka
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Marie Tulin
Original Author
9 months ago
last modified: 9 months ago
GG not the least bothered by ” dont treat” option. they are small but ill make them tough it out. or theyll die. No time for coddling weakings

Do i remember that rjodies in full sun may be more susceptable to bvw?

yes, My yaks and most others

are not bothered. They are pristine though few bloomed this year becsuse of out bizzare and very damaging spring weather phenomenon.

The one i want to save is ”Percy Wiseman” which has proven a weaker plant than i anticipated. Fussy about exposure, lots of branch breakage and die back.It is so lovely; i covet it.

tx for article will read

clarifation: im not mourning isotox being taken off the market. i used it once about 20 years ago and th warnings were so alarming and the smell so vile i never used it again.

interesting article. rather reassuring

black vine weevil active on rhodies

Comments (3)

gardengal48 (PNW Z8/9)

davidrt28 (zone 7)

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black vine weevil active on rhodies

Comments (3)

gardengal48 (PNW Z8/9)

davidrt28 (zone 7)

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Marie TulinOriginal Author

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Marie Tulin
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