Check Spruce Trees and Roses Now!!!!
Even though spruce trees and rose bushes seem poles apart in what might be a problem for them, right now both have a problem that is very similar in cause and the damage done. The larvae of yellow headed spruce sawfly and rose sawfly both eat their host plants. And in many instances, they can do extensive damage. Spruce trees have been severely damaged by repeated annual feeding by the sawfly larvae.
It is very unusual to have the spruce sawfly larvae this late in the summer. They are usually an early to mid- June problem. But some have been observed in area trees. The yellow headed spruce sawfly larvae are hairless caterpillars which are green with yellow/tan stripes down their sides. They are very small which makes finding them very difficult when they first start eating the tree needles. They are much shorter than a spruce needle, and when in their early stages are not nearly as wide. So they can lay motionless along a needle and not be easily seen. As they grow, the damage will be more evident, and they will be larger and more easily found.
The rose sawfly is a tiny green worm which is about the same color as a rose leaf. The first sign you have them is holes in the leaves, and leaves that are eaten except for the veins. Holding a white sheet of paper under a rose branch with these signs and firmly tapping it will usually get some to drop on the paper where they are easy to see.
If left uncontrolled, both sawfly larvae will, when reaching their peak size, crawl to the ground. Once there they will burrow in the ground, pupate and over-winter. The following year they will emerge as adult sawflies which will mate, lay their eggs on either spruce or roses, and the process will be repeated. So there is the potential for the feeding damage to worsen each year if they are not controlled.
On small spruce trees and on roses, a hard spray of water from a hose will wash the small worms off and they likely won’t be able to get back on the plant. Horticulture oil, insecticidal soap, Spinosad and neem oil all can be mixed in water and sprayed on both. All will control the larvae without injuring bees, butterflies and other pollinators.
On large spruce trees, the water can be used if you have only a single tree. But if there is a number of them, in addition to the above mentioned products, having an insecticide applied with a high pressure sprayer can be done. Sevin, pyrethrin, permethrin and Malathion can all be used to control the larvae.
Ken Eraas is horticulture assistant with NDSU Extension Service/Ward County. He can be reached at firstname.lastname@example.org.