"oystershell scale on knockout roses"

henry_kuskaMay 8, 2014

"OYSTERSHELL SCALE ON KNOCKOUT ROSES. Joe Boggs noted that the widespread winter dieback of roses, including Knockout Roses, may have an up-side: cutting and removing winter damaged stems can also help to remove pests and pathogens. Joe reported that as he was pruning dead stems from his Knockout Roses, he came across a heavy OYSTERSHELL SCALE (Lepidosaphes ulmi) infestation on one of his rose plants. On a bright note, Joe observed numerous scale bodies with round parasitoid emergence holes in their coverings (tests); evidence that bio-allies were providing some help with killing the scales!

Oystershell scale is tiny with females measuring no more than 1/16" in length. Their elongate and slightly convex shape causes the scale to resemble miniature clam or oyster shells; thus their common name. Their size, dark gray to brown color, and slight banding cause the mature females to blend-in with the bark making low populations difficult to detect. As with all armored scales, the oystershell scale feeds by inserting their piercing-sucking mouthparts into plant stems to withdraw nutrients from non-vascular stem cells. Since they do not extract juices from vascular tissue, oystershell scales do not exude the sugary, sticky "honeydew" that is associated with "soft" scales. Thus, black sooty molds do not develop to help disclose an oystershell scale infestation.

The scale has a wide host range and may be found on over 130 host plants including trees as well as shrubs. Although this scale has only one generation per year in Ohio, undetected infestations can rapidly build within 1 - 2 years to levels that cause significant plant injury including branch dieback and even plant death. Unfortunately, this is one of the most difficult scale insects to control. Removing and destroying heavily infested stems is a recommended "first step" in an oystershell scale management program.

The scale spends the winter as eggs protected by the bodies of dead females with the eggs hatching in mid-to-late spring. While the resulting mobile first instar nymphs are susceptible to standard contact insecticides including soaps and oils, if the infestation is heavy, the bodies of dead females may protect some crawlers from contact with the insecticide. Systemic neonicotinoid insecticides are effective against soft scales, but some, including the imidacloprid (e.g. Merit), will not kill oystershell scale or other armored scales. Dinotefuran (e.g. Safari) is a highly soluble neonicotinoid insecticide that moves rapidly into plants and has been particularly effective against armored scales as well as soft scales. However, insecticide applications should be coupled with selective pruning to reduce the overall oystershell scale infestation."

Here is a link that might be useful: link for above

Thank you for reporting this comment. Undo
seil zone 6b MI

Well good! At least this awful winter was good for something. It certainly wasn't good for my roses!

I wonder if it will prove to have taken down populations of any other pests like aphids, thrips and Japanese beetles. That would be nice, wouldn't it!?

    Bookmark   May 9, 2014 at 8:11PM
Sign Up to comment
More Discussions
Rose Fields
La Sumida off the Patterson exit in Santa Barbara,...
Is this Drop Dead Red or Legends?
My garden fell in a state of disrepair for about two...
Deja Blu vs Dr. John Dickman
I have and like very much Deja Blu. It looks similar...
Maryl zone 7a
Zone 5 Rose Gardeners "What's Your Favorite Rose'?
Please share your favorite rose. Which one do you...
Is it just me or is RU shipping really late this year?
Now, I will admit that I didn't place my order until...
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™