Laurel Disease

Asked November 14, 2020, 1:40 PM EST

What may I use to combat white powdery looking inner branches on our Atolewkens. ( Mountain Laurel } I have already lost one shrub and i and one other has the same thing but hasn't lost it's leaves as yet. Help there are 5 more mature shrubs. Craig

Maryland

1 Response

Hello Craig,

Cherrylaurel (distinct from Mountain-laurel and the most commonly-used evergreen between them) is vulnerable to a pest called scale - tiny sap-sucking insects whose populations can build up to numbers high enough that they are quite prominent on the bark. In this case, the type of scale Cherrylaurel contracts is white in appearance and can look a bit "snowy" when bark is pretty thoroughly covered. We commonly see this issue crop up on types of Cherrylaurel like the variety 'Otto Luyken'.

Here is more information about this scale: https://marylandgrows.umd.edu/2019/09/25/qa-what-is-this-white-growth-on-my-cherry-laurel-shrub/ As recommended in the article, you can try treatments of horticultural oil, starting soon as plants go dormant as temperatures cool. Check the product's label to see if any specific temperature ranges are suggested for treatment, as weather that is too cold or too warm could either render the spray ineffective or potentially damaging to the plant tissues themselves. Repeat treatments will be needed to assure all scale are exposed to the oil and controlled, so continue to monitor the plant next growing season and re-treat as needed. As with any contact-killing insecticide, thorough coverage of all plant surfaces (in this case, mainly the branch bark) is important for effectivity.

Given the size and quantity of plants you'll need to treat, you'll probably need a hose-end spray bottle (one which is designed to attach to your hose nozzle and dilutes the oil as water passes through it) or a concentrate which you mix-up yourself in a separate sprayer. If mixing yourself, be sure to follow dilution instructions on the label, as too dilute a solution won't work effectively and too concentrated can harm the plant. Horticultural oil does also come in a RTU/RTS (ready-to-use/ready-to-spray) bottle, with no mixing or hoses needed, but the coverage from one bottle won't be enough for all of these plants or for multiple follow-up treatments.

In case other factors contributed to the Cherrylaurel's demise (or are still stressing the surviving plants), here is another article about potential problems this plant can experience: https://marylandgrows.umd.edu/2019/01/07/qa-whats-wrong-with-my-cherry-laurel-shrubs/

Miri