Tuesday, June 23, 2015

Black Scale on Purple Leaf Sand Cherry (Prunus x cistena)

I see shrubs in rough shape all the time.

From afar, this Purple Leaf Sand Cherry didn't have the usual deep purple leaves for this time of year. It was a dead giveaway of something wrong.  Up close, I was in shock.


Sticky, bumpy and mouldy stems point to a major problem.


Black invaders were sucking sap on EVERY stem.


The worst on newer growth.


Then seeing scale nymphs all at the base too!  These young, grey coloured, softer scale insects have emerged from underneath old brown female scale insects, and were making their way up the main branch to the tender stems to feed. This could be Lecanium Scale, but I am not 100% certain.



Here, you can see both sizes and life cycles. I am not sure if they have females which can reproduce parthenogenetically (without mating), but boy oh boy - there were thousands.

The females usually lay eggs in spring and the crawlers hatch from May to June in most species of Scale insects. Now, they molt and turn into instar (smaller juveniles) before becoming large adults. They feed by sucking sap and excrete honey dew which drips on branches below; causing sooty mould. It's quite the mess maker at this stage.


Here, I removed some large black females and you can see some nymphs coming from her underside.



HOW TO CONTROL

I made a tough decision:


I coppiced the entire shrub down to nubs. The situation called for heavy pruning anyway. Coppicing can force new growth right from the blunt cuts. Perhaps not the best time. But to leave it in the state that it was in, was too difficult to manage.

A treatment of dormant oil before buds began to swell in March would of been ideal. It was too late.

Cutting away and removing from the location was the only way I could control such heavy populations of scale.

One small stem remained. In a few weeks time, many more will emerge again.

8 comments:

  1. Thank you. Your information is the best with the pictures mixed with the simple descriptions. I looked at all the other sites, and I'm so thankful forr how you've presented yours. Diagnosis and solution were so easy to follow. and so specific. No threatening paragraphs overwhelming to understand.

    I am relieved to have your blog to come to when I have any other problem. Bravo!

    Alaskan facing first illness and freaked out.

    ReplyDelete
  2. Thanks L.Susan Miller! I do this blog to help those of us who are all learning in the process! Don't freak out! lol

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  3. Thank you for your information I have this same problem with my sand cherry tree in addition to an infestation of ants going up and down the branches I am assuming one has to do with the other going to cut the tree down today

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  4. Thank you for the information I am going to cut down my sand cherry tree today as I have the same problem in addition to an infestation of ants going up and down the branches I tried treating the ants with insecticide but they came right back

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  5. Given that it's now mid-July, folks, be aware that during the heat of the next month or two, the plant may not respond in the same way during cooler temperatures. Last year when I did this, it was a cooler, wet summer and the sand cherry did develop shoots from the base. This summer has been exceptionally dry and hot. Perhaps wait until next spring and try to dislodge some of the scale with a heavy blast of water spray. Cut harsh, right down in the spring. It will bounce back much more readily and not be stressed as it would this hot summer. Cheers.

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  6. Hello Heidi, I work at a garden center in Toronto. A customer came in with a branch of a sand cherry that seemed to be going in to its fall colour. leaves look very similar as the ones in your photos but the branch didn't have any scales on it. Can't really seem to figure out what was wrong with it. just wondering if you had any ideas? Thank you

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  7. Hi there - trying to diagnose problems with Purple Leaf Sandcherry via wording - well, it won't happen. Purple Leaf Sandcherries are in "Prunus" family and have varying problems. Disease related and abiotic. Given this summer has been extremely dry and hot, Purpleleaf Sandcherries become susceptible to a variety of insect and disease problems - even dieback or another vascular disease. Sometimes, when it's so hot, the inner leaves change colour and drop. Hard to say over a blog conversation.

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