Saving a lilac
As I was pruning my 14-year-old lilac last month, I noticed that this past fall/winter it was taken over by scale. Some of the branches are entirely covered and it has thinned out substantially this year. Although I've tried to scrape some branches, I don't think I can accomplish the entire thing due to size - it's about 10' tall. The same can be said about applying Neem oil. I was planning to spray the branches once the crawlers emerged, but the blooms are now open and I'm concerned about affecting bees should they emerge within the next few weeks. I've been researching cutting the bush back to about 6-8" above the ground to save it instead. Is it too late in the year to do this if I wait until flowering subsides around the end of this month? Thank you for your help.
Larimer County Colorado trees and shrubs
Wow! That is a very healthy population of scale! Great photo. More than likely this is oystershell scale: http://extension.colostate.edu/topic-areas/insects/oystershell-scale-5-513/
One thing to point out is that Neem should not affect bees or other pollinators, because the product must be ingested. Since the bees are only feeding on the nectar, they shouldn't be affected. But it's always good to take precautions.
Renewal pruning, removing it to 6-8" above ground, is best done in late winter/early spring, prior to budbreak. Doing it after it flowers may not give the plant time to recover before the season ends. What you could do is remove the 1/3 most affected branches following flowering and cut them to the ground. You can continue in this manner for three years. This would work best if the thicker, older branches are the most affected by the scale.
If you don't want to use neem, then consider using a horticultural oil, which would be applied during or just after the crawler stage. Since our spring is so early, I would start checking now for crawlers. They generally start to move in mid-May and we're 3-4 weeks ahead of normal, so now might be the time to treat. Please let me know what other questions you have!
Thanks Alison! What precautions should I take to prevent affecting bees and other polinators? Also, if using neem oil, do I apply it after the crawlers emerge or do I need to instead use horticultural oil at that point. I'm not clear on when the best time is to apply neem. Thanks again!
The oil would work by smothering the crawlers (so you would apply it when they are crawling) and the Neem works through ingestion. What I would recommend is you contact the company of the Neem product you buy and talk to them about the timing on scale and flowering plants. Since there are different products, it probably would be best. Also, ask about spraying while the plant is in flower.
But here is information from UC Davis on using Neem (http://ipm.ucanr.edu/PMG/PESTNOTES/pn7408.html):
Nonresidual, Contact Insecticides
Where plants can be sprayed, complete spray coverage of infested plant parts with horticultural oil at the proper time provides good control of most scales. Horticultural oils (e.g., Bonide Horticultural Oil and Monterey Horticultural Oil) are specially refined petroleum products, often called narrow-range, superior, or supreme oils. Other nonpersistent, contact sprays for garden and landscape plants include insecticidal soap (Safer Brand Insect Killing Soap Concentrate II), neem oil (Bayer Advanced Natria Neem Oil Concentrate, Green Light Neem, Garden Safe Brand Neem), canola oil (Bayer Advanced Natria Multi-Insect Control), and other botanical (plant-derived) oils.
These insecticides have low toxicity to people and pets and relatively little adverse impact on the populations of pollinators and natural enemies and the benefits they provide. To obtain adequate control, thoroughly wet the infested plant parts with spray, typically shoot terminals and the underside of leaves. More than one application per growing season may be needed, especially if the targeted pest has more than one generation a year. Thorough spray coverage is especially critical when treating armored scales and oak pit scales as these scales are generally less susceptible to pesticides than soft scales.