Aspen trees - Knowledgebase Question

Littleton, Co
Question by dayrondarl
March 2, 2011
Is there any way to stop black oyster shell on aspen trees. One tree has it about 2 ft up the trunk and the other about 8 ft high. I have been using a liquid that I delute and pour it around the base of the tree. any other suggestions.

Answer from NGA
March 2, 2011


Oyster shell scales are quite common on woody plants in your gardening region and they are difficult to control but if you keep after them, you'll eventually eliminate the pests. The scale adults overwinter with a cache of eggs hidden beneath their protective outer shells. In late May or early June the eggs hatch and the crawlers head out to find suitable places to attach themselves on the trunk or branches. The pests are most vulnerable to control at the crawler stage so that's when you'll want to control them. Use horticultural oil to suffocate them (also called dormant oil). Since oils can damage the leaves of your trees you'll want to spray prior to the trees leafing out, or you'll want to keep the spray off the leaves and on the trunk of the tree. Applied as recommended on the label, horticultural oil won't damage your tree. I'd spray the adult scale insects now with horticultural oil (in hopes of suffocating them and the eggs before they hatch) and spray again in late May to suffocate any eggs that have hatched into crawlers. You may need to repeat this process again next year. Hope this helps you control those pesky scale insects!

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