1 - Extreme pruning of euonymus now can cause problems in some parts of New Mexico.
Q. I live in the UNM area of Albuquerque and have five mature euonymus bushes at my front door (facing due east) which are shaded by honey locust trees at this time of year. The scale infestation is terrible this season and I am spraying the bushes with a canola oil and water solution (about 2:1 or 1:1). Since the temperature cooled this past week, the scale activity increased dramatically and leaves are turning yellow everywhere.
Complicating matters, I tried a new yard service recently (2.5 weeks ago) and the gentleman 'lost' himself while shaping the bushes. He just about completely denuded three of the five bushes of all the leaves. With the scale infestation attacking the few leaves left on the three bushes, I fear all the leaves will die and the bushes will not survive.
Do you have any suggestions on improving the situation and saving the three denuded bushes? What solution of oil and water is best? And how often should the application be done? I worry about too much oil smothering the leaves, making them incapable of breathing.
A. This is a very difficult situation. The good news is that the work was done several weeks ago (by the time this is published). The extreme pruning will result in the euonymus shrubs attempting to replace the leaf surface that was pruned away. In Albuquerque the first killing frost may come about the third week of October. That may not be enough time for the new growth to mature and be able to survive the cold. However, it may be enough time. The location (microclimate) in which the plants are growing will be important. A warmer microclimate that delays the onset of cold weather or a late onset of winter will be very helpful.
You can help by not encouraging excessive growth at this time. Do not give your shrubs nitrogen fertilizer now, even though new growth is developing. Nitrogen will stimulate more new growth.
Irrigation is necessary as new growth develops, but you should minimize irrigation to encourage the early cessation of growth. There are two reasons for this. By minimizing growth at this time, you will reduce the depletion of stored food reserves in the shrub required by the new growth. If the new growth is killed by the winter, there may be enough stored reserves in the shrub to begin new growth in the spring. The second reason, is that by minimizing growth now, it will mature more quickly and have an improved chance of surviving the winter.
The oil sprays you mentioned are a good treatment for scale insects but be sure to use a product labeled for use in managing scale insects. There are several types of oil sprays. Some are based on canola oil and others on refined mineral oils (less harmful to plants in leaf than the old dormant oil sprays). Most should not be used during the hot weather we have been experiencing, but as the weather cools, you can apply these sprays to plants with leaves on them. Because there are several different formulations of oil products, I cannot tell you specifics for applications. It will vary between formulations. Follow the directions on the label regarding frequency of application and dilution rates.
The best thing you can do now is remove any leaves and debris beneath the shrubs. The dead leaves and twigs contain the eggs and, perhaps, some living scale insects that will reinfest your shrubs. Sanitation now and later will help you to manage this pest. The important thing is to move these sources of reinfestation away from the euonymus. This particular insect, the euonymus scale, only infests euonymus so it can be composted in a location away from the euonymus, even if other types of plants are nearby.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: firstname.lastname@example.org, office: 505-865-7340, ext. 113.
For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!