Serious eunymous problem

Asked August 20, 2018, 1:26 PM EDT

I have two huge euynomous bushes, perhaps 9-10 feet tall, which I have had for decades. This summer they developed euyonomous scale--I'm sure of the diagnosis. I was out of the country and the problem was not dealt with in a timely fashion. The damage has been huge. When in the fall can I deal with this, and will the existing scale recur? What is the best schedule of treatment? Is dormant oil the thing to use? Please supply all available information as I'm desperate. Many thanks,

Montgomery County Maryland

5 Responses

Euonymus can be sprayed for big infestation from May through June and also from August through September. You'll be aiming to kill the crawlers, the immature stage, which is not protected by the scale cover.

Use horiticultural oil or an insecticide with pyrethrin if the oil is not sufficient. You have enough time to spray more than once if necessary.

Do a dormant spray as presented on our webpage:

Thanks for answering. Two followup questions:

1) Should I spray after the immature stage--eg, after September--as a preventive for next spring? Will it help? If so, how many times?

2) Are the insects still sitting on the plants (leaves and inner branches) going to spread? I sprayed them with a high pressure hose, but there are still a lot left. Or are these now harmless for the future?

Please read the links provided.

1. The adult stage is not going to be susceptible to insect sprays. You have to spray the immature stages.

2. As long as they are alive, they can spread.


Please excuse me for continuing to bother you, but I need to understand your last answer. Does it mean that it is very possible that the scale I still see on the plant are alive? And will not die off in the cold of the winter?

And if so that they must be sprayed during May-June?

Linda Koenig

If you spray now with a horticultural oil, you are targeting the immature stage, the crawlers. They are yellowish orange. You can apply a double sided sticky tape to monitor and look for crawlers. Also, look for lady beetle larvae and adults. They help to control the scale. Do not spray if black lady beetles with two red spots are abundant.

You will probably get the best control with a dormant oil spray when the plants are dormant. This will be when all the trees have lost their leaves. A dormant oil will control light bark infestations. You will have to get good coverage. Spray the whole plant, bark, and underside of the leaves. This is a contact material. Temperatures have to be above freezing within 24 hours after you spray.

You will have to monitor again in the spring and spray if needed May through June with a horticultural oil.

Since the plants are so large control may be difficult. You may want to hire a landscaper to spray. Also, you may want to replace Euonymus japonica with Euonymus kiautschovica where possible as this is resistant to the scale. Or replace with another type of plant that matches the site and mature height and width.