Help!? what's eating the snowball viburnum/what can I do?

Discussion in 'Outdoor Gardening in the Pacific Northwest' started by lduggan, Sep 22, 2010.

  1. lduggan

    lduggan Member

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    Hello,
    This is my first ever time on the forum site, so bear with me please. :) And thanks in advance for any help or advice. Happy gardening!

    Our backyard (south west coast, BC) is in trouble, in part due to some kind of insect on the established snowball viburnum [kind with flowers that start green and turn white]. The same cycle of leaf and blossom decimation has occurred for the past 3 years on the snowball viburnum in my backyard: 'tree' forms good leaf growth and blooms, then from the bottom up the leaves are skeletonized and blossoms brown and shrivel.

    Last fall I tried to prune some of the branches that were crossed and crooked and rubbing, particularly from the center of the shrub, as well as all the dead and broken branches. This spring the shrub produced new growth and flowers that made it appear to almost be completely healthy, but then again succombed to ???

    The plant then seemed to rebound somewhat when I removed as many affected flowers and leaves as I could--mostly on lower/outer branches--and produced some new leaves, which were then skeletonized.

    Also, foliage and new growth seems to only appear at about 5ft and up: the branches/trunks below 5 ft are bare of any new growth.

    And on the plants below/next to the viburnum, the leaves where affected/infected virburnum blossoms/leaves fall get holes in them--i'm assuming from same insect?

    But the insects that are all over the viburnum and all the plants nearby (old shrub roses, pieris, hosta, honeysuckle, blueberry) spring off the plants when the plants are disturbed, then fly short distances to land. They are a very pale brown, about a cm long, and the only image I've found that looks like them to me was identified as a leafhopper. This year the established lacecap flowered viburnum 15 ft away was infected/affected for the first time [same skeletonized leaves, worst at bottom]. i have noticed the insects as far as 40-50 feet away on a clematis and black-eyed susans.

    Do you have any idea what might be eating our snowball virburnum? Or any other cause for its sad demise?

    If the answer is hort oil or spray or something, any suggestions about where I can get info on appropriate times for application, when to do what, what to watch for during which season, etc?
    ---------------------
    And for those of you who like a good, complex problem, or sharing your vast knowledge and experience:) :

    I should mention that I'm sure there are larger issues at play in the yard that have worked to weaken the shrubs and plants, as evidenced by the aphid-infected roses and honeysuckle and general lack of maintencance of garden.

    As I see it, the maintenance/cultural/physical factors that are weakening the virburnum and surrounding shrubs include:

    1. pruning--maintenance and of damaged parts--appears to never occurred on all shrubs, and they are now all above 8ft with 'trunks' and canes of 2-3 inches minimum, so I think they're quite old.
    question:
    on an old possibly ill or infected shrub ie viburnum, is pruning of any sort possibly going to kill it or weaken it? Or will pruning possibly result in branches that won't produce new growth?

    2. same shrubs not staked or supported i.e. roses:often fall to 70 degrees en masse, and/or have weak, thin v tall main branches i.e. beauty berry and lilac

    3. branches of shrubs are criss-crossing/rubbing, too crowded in center and at crown
    4. beauty berry and lilac-also mature/old-have likewise not been pruned and old branches/trunks have peeling bark and huge streaks of fungus
    5. soil is extrememly clay-ey and weedy
    6. Leaf etc. debris has never been cleared from soil and garden beds never mulched [for past 8 years at least]
    7. top soil is washing away yearly from the beds and has never been replaced
    8.the snowball viburnum in question is in a dark, cool corner of yard so although it's south facing, bottom 4-5 ft shaded much of the year.


    Unfortunately for me, I am just the renter here, so the landlord does the gardening and I've not intervened yet other than some emergency pruning, weeding and debris clearing when he's away. Obviously the yard needs better maintenance and I'm hoping the landlords will take my advice and follow some suggestions re mulching, building up the beds, pruning etc.

    Anything glaring that I've missed? Any ideas that jump out at you? I'd love suggestions and any resources you think I need to access. THX!
     
  2. Eric La Fountaine

    Eric La Fountaine Contributor Forums Moderator 10 Years

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    As far as the viburnum goes, do a search for Viburnum Leaf Beetle, Pyrrhalta viburni. I don't really know much about pest control, but it sounds like it might be the problem. Plants are quickly defoliated by this pest and it seems to fit your description. This pest has been spreading rapidly in the area the past few years.
     
  3. lduggan

    lduggan Member

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    thanks Eric! will do,
    Laila
     
  4. dt-van

    dt-van Active Member 10 Years

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    Almost certainly the leaf beetle. I understand that pruning in late fall to remove the branches where most of the overwintering eggs are can help. Last year our evergreen viburnums were severely damaged, but this year (although we did nothing much) they are fine. I though perhaps the early cold snap last winter had killed them, but I guess not if yours are bad again this year.
     
  5. lduggan

    lduggan Member

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    Re: Help!? what's eating the viburnum/what can I do?

    thanks! yes, I've managed to find some pretty good info on several sites, and it looks like the best way to 'attack' the problem--assuming viburnum leaf beetle--is to get rid of all egg-infected plant material once the adults have finished laying, usually by the first frost (October-ish).

    note to all: since the beetles migrate, your neighbours' problem could soon be yours/ours, so feel free to share the news, spread the word, etc.

    I couldn't find info on native BC viburnums and VLB. Anyone?

    sites for anyone interested:
    single site with greatest info-incl management of VLB, timeline of VLB lifecyle, etc:
    http://www.hort.cornell.edu/vlb/index.html
    [slightly out-dated, but the best I could find nonetheless]

    re viburnum leaf beetle (VLB) in BC [it has been in East states/Ont for many more years]-
    http://www.agf.gov.bc.ca/cropprot/newpest.htm


    general 1 pg VLB fact sheet-pdf-
    http://www.entomology.cornell.edu/cals/entomology/extension/idl/upload/Viburnum-Leaf-Beetle.pdf

    list of sellers of biologicals in North America[1997]:
    http://www.cdpr.ca.gov/docs/*******/ipminov/bensup.pdf


    If anyone wants more about VLB:

    A type of European Leaf Beetle, the VLB first arrived in '47 but was noted as breeding populations in 1978 in Ont and NY state in 1996 for the astounding damage to viburnum populations there. As Eric La Fountaine indicated, it's been establishing itself out west, noted in BC since 2001 and is now "officially" here and pest-y in BC.

    Since our viburnum (European, snowball, green flowers turn white) has been infested several years, it may not survive another year of infestation. But as mentioned, another viburnum in the yard was infected for the first time this year, so action is necessary regardless.

    Since both the pupae and adults feed on viburnum plant, and eggs are laid in it, and since adults can migrate or hop off and return, there's no single easy way to manage VLB.

    If you can identify the egg-laden branches, this is the top way to fight the beetle infestation and not harm anything else. The internet has good pictures of viburnum branches with eggs, and I think I'll be able to identify them fairly easily. Between Oct and next Apr it looks like pruning out and destroying egg-infested branches is all that can be done, and hopefully it will be enough.

    A few years back it was proposed that applying sticky rings at base of plant stems/trunks in about May-early June could very well stop all larvae from migrating to ground to pupate, since it was discovered they climbed down, not simply dropped. I didn't find any info about whether this technique was effective, but I guess it was posited that after eggs hatched in april/may, putting a sticky barrier such as Tanglefoot tree pest barrier around the base of the shrub could keep larvae from reaching the soil to pupate.

    Addressing the pupae in soil is not recommended since damage to roots will likely be worse, esp if plant is already weakened from previous years.

    It looks as though, in addition to pruning and applying sticky rings, several beneficials do predate on the VLB, even though the VLB is an imported pest. According to the cornell website, 'adults and larvae of multicolored Asian lady beetle and larvae of lacewings will eat considerable numbers of viburnum leaf beetle larvae, and spined soldier bugs will eat both larvae and adults of viburnum leaf beetle.'

    Good luck, happy hunting,

    L

    [evidently, systemic pesticides are considered most effective single approach, but from what I read about it, it's as nasty as they come: harmful to birds, harmful to bees, not to be applied if rain is forecast, if near fish habitat or near drain into aqua habitat, etc. No thanks!]
     

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