Tuesday, April 23, 2013

Oyster Scale - Lepidosaphes ulmi

I don't see Oyster Scale very often, but on this young lilac, it was hard to notice. Deep brown and shiny bark was what I hoped to see. Instead, these grey, matted blotches point to something else.

It's a thick coating that won't come off easily.

Even with my nail scraping them off, it's a tough go.

You can clearly see why they are called Oyster Scale with this close up.

Like my post on Euonymus Scale, this pesky insect is hard to control.  Given this lilac was newly planted and situated with others, I will have to remove it - preventing its neighbours from getting infested. This one is really bad. By late summer, the scales excreted poop will turn into sooty mold, which will further change the bark colour to a brown black.

Treat with dormant oil before bud break in spring and again just after the leaves have fallen in the autumn.  For a more natural control method: spray with a hard water spray - during this time of year when the leaves have yet to emerge. You can repeat the hard water spray throughout the summer months, just be sure not to damage leaves. This dislodges many of the adult scale and their nymphs. You have to REPEAT this method, over and over - to dislodge them. But it works.

Pruning the worst of the branches out helps too. Reducing their numbers is key. By all means, you can scrape the scales off with your finger nails (eeew) or a soft brush after they have been moistened (by rain or your water spray). This will drastically reduce numbers, but be careful not to damage tender bark in the process.

Feed and nurture infested shrubs like this. It'll help them bounce back.

HINT:  given this plant is young and newly establishing... It was probably infested at the nursery. Folks, look carefully at your shrubs and plants coming from garden centres. This Oyster Scale feeds off of several shrubs, including: Willows, Cotoneaster, Dogwood and young Ash and Maple trees. You don't want to bring a shrub home with this insect problem.  It will travel, infesting other plants.


  1. Oh dear. That's a crying shame. I just discovered an early case of scale on my young Cornus kousa. I scraped off all I could see with a thumbnail and will be watching it like a hawk from now on. The past couple of summers put extra stress on woody plants, especially. Good luck.

    1. Thanks for commenting, Helen - ya, this lilac was 1 of 10 planted as a grouping. Such a shame. But you're so right in saying our last summers have put serious stress on our plants. Keep watering and keep a close eye on your Kousa! Cheers!


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