Well, Rose Sawflies are back, for their annual spring appearance. These individuals were found in a garden in Green Hills area of Nashville on Friday.
They are just hatching and beginning their big feast on rose leaves. They can munch up a lot of rose leaves within the few short weeks that they are feeding. Then they drop to the ground and enter their pupa stage, and are harmless to the rose. Often the damage isn't noted until it's severe or after the sawfly larva are gone.
Inspect your roses now. Look on the underside of the leaf for the pale green creature that looks like a caterpillar. Control it by: spraying with a hard stream of hose water. Organic pesticides include Neem and permethrins. Bt is not effective.
Don't apply pesticides if there are no pests present.
Most healthy rose plants will survive unless completely defoliated. You can prune off the affected leaves and of course shrub roses, like Knockout roses, will probably bounce back and bloom on the new growth.
Here's a great link with a longer discussion of sawflies and Integrated Pest Management
http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advice-tips-resources/pests-and-problems/insects/sawflies/rose-and-pear-slugs-sawflies.aspx
Photographs © 2014 Mary Boyd
