Infestation of Euonymus in planter

(Question)

I live in a Leslieville townhouse in Toronto and our outdoor space is on the roof where we have a small euonymus tree. (We did not purchase the tree it came with the house so I don’t know the specific type). The tree appears to be infested where the trunk and branches are covered in a white bumpy substance and there are small spiny insects crawling on the plant and making webs. I would say that it is scale but the pictures online show them mostly on the leaves of the plant, whereas on ours, they are mostly on the trunk and branches. The leaves on our tree are fairly untouched. Many of the branches have become brittle and some of them did not grow leaves this year.

I’ve attached a picture and you can kind of see one of the spiny insects on the whitened branches.

I’m hoping you can tell me whether there is anything I can do to save the tree or if it is probably to far gone at this point to save.. I would like to try and save it if I can. Please let me know if you have any suggestions!

(Answer)

So sorry to hear of the infestation.  Unfortunately, the photo you sent does not clearly show what you describe. However, euonymus scale sounds highly likely.  I’d suggest that you try and save the plant – it may take quite a bit of effort, but will be worth it!

Last year, Ontario’s Ministry of Agriculture and Food and Rural Affairs (OMAFRA) issued an alert about euonymus scale, which attacked both euonymus grown in containers as well as in the ground. You will see from the link provided in that alert  that scale can affect the entire plant.

You might be interested in an earlier question we received (posted in March 2014)  for suggestions and helpful links. As your plant’s infestation is significant, the use of horticultural oil to suffocate the beasties when they are most vulnerable (they later develop armoured scales, which would be resistant to oils and other substances) is likely the best option. Use a light summer-weight oil (a mixture of horticultural oil and water), which can be applied throughout the growing season – usually in early June and then again in late July and August.  Horticultural oil may harm some plants, so check with your local garden centre when selecting a product to use.   Insecticidal soaps may also work well.

In general, scale insects lay eggs in late April/May and these hatch into nymphs (crawlers) after 2-3 weeks. The crawlers explore the plant and start to feed, then in 4-6 weeks become adults. A second crawler generation will emerge in late July/August.  So timing your “attack” on scale is critical, since best results are achieved when you target the insects at the crawler stage – when they lack protective armour (which resists oils and other substances).

One way to determine precisely when the crawlers emerge is to use simple tape traps (see the UC Davis reference link below).  As well, if applicable, control the ant population in the area, since ants (seeking honeydew produced by scales) protect scales from their natural predators.

Make sure that your plant is sited so that it gets good air circulation, as scale is usually worse when plants grow close to buildings.

And don’t over-fertilize – this can increase scale populations.

As it is now near the end of June, you could prune back the branches that are most heavily infested. (Next year, prune the euonymus back to the ground as late as mid-spring and  protect emerging shoots from infestation by spraying.)

Next year, consider using dormant oil (as its name indicates, this should be applied during the dormant season – late winter or early spring – this smothers the females before they have a chance to lay eggs). Do not use dormant oil once leaves or blooms start to emerge.

Finally, you will see that some references recommends pesticides, which I suggest you avoid, as these may adversely affect pollinating species, like bees.  Their use may be restricted, too.

Here are some good references about scale:

  • UC Davis’ Statewide integrated pest management program. Scales. (This resource had the most comprehensive information I located)
  • University of Minnesota Euonymus scale, which also notes that scale can infest leaves, stem or fruit of the plants.
  • Penn State Euonymus Scale

All the best!