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Watch out for sawflies on pines and roses

Jeffrey Hahn, Extension Entomologist

There are two kinds of sawflies that are active right now, European pine sawfly and roseslug.  European pine sawfly loves pine, especially mugo, red, and Austrian pines.  It has a black head with dark grayish green and light grayish green stripes.  They grow as large as one inch long before they are done feeding.  They chew the old needles of trees and shrubs.  While in many cases, defoliation is not severe, they do have the potential to do extensive damage.
European  pine sawflies. Photo: Jeffrey Hahn, UMNExt

Roseslug is a slug-like translucent greenish larva that grows no more than 1/2 inch long.  They windowpane feed the leaves of roses, i.e. they feed on one layer of leaf tissue between the veins.  Damaged areas are opaque at first but eventually turn brown.  Damage can range from minor to severe.
Roseslug sawflies. Photo: Jeffrey Hahn, UMNExt

Both of these sawflies only feed in the spring and are done by June.  If you find these insects on your plants, the first consideration is how large are they.  The closer they are to full grown size, then the closer they are to finishing their feeding.  When they are at that stage, treating does little to protect the plants.  If you find them at this stage, your best bet is to just ignore them for this year.  If they are a size where they are worth treating, usually about 1/2 full grown size or less, there are several options.  You can crush them (wearing vinyl gloves of course).  If you are interested in a low impact insecticide, try insecticidal soap or spinosad.  You can also use a residual product, such as permethrin or lambda cyhalothrin.

For more information, see Sawflies of trees and shrubs.
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