Tuesday, February 26, 2013

Lacebug…coming to a Rhododendron near you?

During our recent Yard, Garden & Patio Show here in Portland I had the good sense to attend a lecture by (beloved) local garden personality Mike Darcy. Before he began the presentation (the topic was “bringing color to the garden”) he shared a warning about lacebug, noting that people were bringing him damaged leaves from their plants over and over again asking what they could do.

This was eerily familiar to me because lacebug is what brought down the huge Rhododendron in my garden last year. Mike identified two ways of dealing with this pest. First you can use a horticultural oil but it is necessary to spray the underside of the leaves, as you might imagine that is a tad difficult. Secondly you can use Bayer Advanced Garden Tree & Shrub Insect Control. The key is to catch the infestation earlier than I did; since by the time I noticed something was wrong with my plant about 90% of its leaves were toast. There is no saving the leaves once they look like this…

By treating the plant your insuring the new growth is healthy. As you know I “treated” my plant by getting rid of it, that’s probably not an option for everyone. After hearing this warning the first thing I did when I got home was look at my remaining Rhody to see how it was doing, so far so good.

Not such a happy ending for my neighbor though. We were standing in his driveway chatting the other evening when my gaze turned to his Rhody…

And then I looked closer…

And I had to tell him he had a problem.

He decided to treat the plant and save it, most of it still looks good so I bet he’ll be successful.

I’ve been looking at other Rhody’s around town as I walk, it’s about 50/50…those with some issues and those with none. Of course it’s hard to really get a good look as it seems most Rhododendrons are planted as foundation shrubs and I’m not comfortable walking up next to people’s houses to check out their plants! Want to learn more? Here’s a page that the local Master Gardeners sent me.

29 comments:

  1. Thanks for sharing! I wasn't aware of this issue and will be checking of of my new rhody's to keep them safe! Cheers, Jenni

    ReplyDelete
    Replies
    1. Hope you're in the clear Jenni...

      Delete
  2. Thanks for the pictures of what the damage looks like, and the warning! I'd like to add a big-leaf rhodie this year, and this is something I'll have to watch for. I hope your neighbor's survives. So glad to see that your other one is doing well.

    ReplyDelete
    Replies
    1. I've got a major crush on the big leafed ones too...so many plants, so little space.

      Delete
  3. Great information! I'm pretty much clueless when it comes to pests other than slugs and the new bane of my existence, wevils.

    ReplyDelete
    Replies
    1. Weevils are pure evil, I'm convinced of that.

      Delete
  4. Will have to keep an eye on this one. Didn't realise that once the leaves turn like that it is too late already...

    ReplyDelete
    Replies
    1. Too late for those leaves, not the whole plant though (as long as you've got some healthy ones.

      Delete
  5. I lost an azalea to lace bug this past autumn. Luckily it wasn't a plant I particularly cared about, but it surprises me to see how widespread the damage has been - I have seen it all over my neighborhood. Examples were posted in the Master Gardener clinic office last time I was there, so I think it must be particularly bad this year.

    ReplyDelete
    Replies
    1. Oh yes, I should have mentioned azaleas too!

      Delete
  6. Interesting, coming from here - a place where hort savvy is obsessed with cold hardiness and water. So much more than those often minor issues, when a plant is adapted. Always something! Bugs...

    ReplyDelete
    Replies
    1. Indeed...it is always something.

      Delete
  7. Uh oh...here in RhodyLand that is bad news indeed. Forewarned is forearmed, right? Thanks!

    ReplyDelete
    Replies
    1. It's kind of shocking when you actually are looking for them just how many Rhodys there are around these parts!

      Delete
  8. I'm curious what's stressing the plants.

    ReplyDelete
    Replies
    1. In my case I'm pretty sure it was lack of air circulation. The plant had grown up into the overhanging privet, over into the neighbors garage and hit plants on the south side of the bed. But in my neighbors case (and the other leaves I photographed) I have no idea.

      Delete
  9. Yuck, that looks nasty.

    Brownie points for you Loree on pointing out the issue to your nieghbour!

    ReplyDelete
    Replies
    1. His plants are so nicely pruned and anchor that front bed, I'd hate to see them have to go!

      Delete
  10. Ouch!!! I still have three rhododendron, I'll have to take a look see!

    ReplyDelete
  11. Scouting for pests is that are common to our key plants is one of those necessities in life that can be made more pleasant with a cold beverage in your hand.

    I recommended getting on a Plant health Care report e-mail list from your closest Botanic garden/Arboretum/State extension program and go out and scout for the pests they are seeing on plants that you have when you receive a new report.

    ReplyDelete
    Replies
    1. Ah this is a good idea (both the beverage and the email list), thank you Jim!

      Delete
  12. Thrips do the same sort of foliage damage on rhododendrons here, especially where they don't have good air circulation, and also attacks many other plants in the Ericaceae family here. For what it's worth, rhodies with fuzzy foliage are largely immune. One caution of using systemics on flowering plants in the landscape is that they can also poison bees, butterflies and hummingbirds, so I don't use them outdoors myself.

    ReplyDelete
    Replies
    1. Yes indeed thrips were one of the pests that was suggested as the cause of my damage last spring. I was told that treatment was the same no matter whether it was thrips or lacebug. And yes, I understand the issue with systemics, another reason why I felt good in treating my plant by simply removing it.

      Thank you for the mention of fuzzy foliage being immune, this is good to know.

      Delete
  13. I saw a lot of this when I was doing maintenance for clients in the Seattle suburbs. Big, old rhodies which had been fine for years (as reported by the clients) were now disfigured. Drought stress is a contributor, I believe. Last summer was brutal, going from super wet to almost record dry.

    ReplyDelete
    Replies
    1. Thank you Tia, and great point about last summer. That would help explain why there is a current outbreak here in Portland.

      Delete
  14. Hi Loree, my Master Gardener class just covered this topic yesterday, so I feel I should share a bit of what I learned:
    Lace bugs are tiny true bugs .13 inches long, whitish tan which cause significant damage to broadleaf evergreens including: andromeda, laurel, pyracantha, rhododendron and azalea. Yellow white stippling on upper leaf surface, underside has "tar" spots. Infestations are more severe on plants in sun. Damage apparent by early to mid-July. While almost never fatal, repeated infestations result in sickly plants.

    Eggs overwinter in crusty brown patches along midrib of leaves. Adults present through summer and fall. Several species attack, they may have different life-cycles. There is probably one generation a year in Oregon.

    Management: proper water and nutrition, keep plants in shade, remove leaves with brown patches of eggs if possible, hosing plants with a strong stream of water on underside helps to remove them, wingless nymphs will not return. I have a list of some resistant cultivars if interested.

    Biological management - release of lacewing larvae have proven successful in one experimental test. Select insecticides to preserve populations of beneficial predators which will help control lace bugs.

    Chemical management - acephate, neem oil, cyfluthrin, horticultural oils, imadacloprid, insecticidal soap, spinosad. Use any with caution, some can harm beneficial insects. Always read labels.

    Well, that's most of it for now.
    I had to trash two azaleas just this week due to a severe outbreak I missed last fall - looked like powdery mildew...mine were not in full sun but were attacked heavily. Oh well, an opportunity to buy more plants is how I see it!
    cheers! happy bug hunting

    ReplyDelete
    Replies
    1. Thank you Tamara for all of this info!

      Delete
  15. AnonymousMay 01, 2015

    Wow...so THIS is what's going on with my rhododendron and azalea leaves.
    I was thinking it was a deficiency of some sort, or maybe too much fertilizer.
    I have had this on my rather large rhodies and a bank of azaleas for years.
    New grown keeps coming up, so I was thinking it would come out of this funk sooner or later.
    I will prune back..even though it's not the optimal time to do so, and spray.
    Thanks for the info,
    :-D

    ReplyDelete

Thank you for taking the time to comment. Comment moderation is on (because you know: spam), I will approve and post your comment as soon as possible!