Those Pesky Sawflies!
Those Pesky Sawflies!
Sawflies are members of the insect order, Hymenoptera, that includes ants, wasps, and bees. Sawfly adults are wasp- like and have a sawlike tube which is used to incise holes in plant tissue for depositing eggs. Unfortunately for gardeners, sawflies often lay large numbers of eggs on a single plant, and the caterpillar-like larvae can devour large amounts of plant material in short order. Sawflies are usually plant specific, so pine sawflies may have many pines as a host plant, and rose sawflies will attack many kinds of roses, but neither will find hibiscus suitable for food.
There are several sawfly species that will shortly be trouble in the landscape. Be vigilant and try to detect them as soon as possible. If you have hibiscus, mugo pine, or roses, you may have already, or will soon see damage from feeding larvae.
This spring the rose sawfly was a problem on many roses, including the insect- resistan Knock- Out ™ varieties. The initial feeding damage from the smallest larval instar was sometimes mistaken for disease, as leaves turned brown over time and then dried up. The larva chew the leaves on one surface, so the other side looked good until the damage was severe enough to cause browning of tissue. Most damage is now at an end, but larva may be sprayed directly with insecticidal soap if needed. Next year, look at the leaf undersides periodically to detect larvae as soon as possible.
Rose sawfly larvae. Photo entomology.wisc.edu
These sawflies are currently beginning to feed on members of the Mallow Family. Larvae are green and have dark heads, and begin feeding on the undersides of leaves, moving to the upper sides as they become larger. To catch quickly, check the undersides of leaves. They will consume every part of the leaf except the veins, and the damage may be confused with that of scarab beetles. Manage these pests by handpicking larvae, or removing leaves having many of them. Cocoons are found on the base of the plants and can be removed and disposed of. Insecticidal soaps or spinosad are effective means of control also.
Hibiscus sawflies and damage. Leanne Pundt photo.
There are two species of sawfly that are serious pests of pines in New England, the redheaded pine sawfly and the European pine sawfly. The European pine sawfly commonly attacks Mugo pines in the landscape, but will also feed on Japanese, Scotch, and other pines. Usually, pine sawflies are found on young trees that are between 1- 14 feet tall. Needle damage first appears as browning of the needles and gradually the branches will become stripped of needles. This is because the larvae feed together in large groups. If all the needles have been consumed from one tree, the sawflies will move to another nearby pine. Best control is when larvae are small to keep damage minimal.
Eggs can be removed if found on needles over the winter. Destroy the material, do not simply discard on the ground. Also, clip off branches that have multitudes of larvae, or try to knock them off into a bucket of soapy water. Summer oils and insecticidal soap can be applied to larvae feeding on ornamental pines. Make sure coverage includes all the larvae.
Sawflies on white pine Photo copyright Pamm Cooper 2013
Sawfly damage to Mugo pine University of Illinois Extension photo
Sawfly adults are hard to spot sometimes, as they appear to be wasps hanging about the garden. But aquaint yourself with the life cycles of the sawflies that are pests in your gardens or landscapes, and check for larva before you see damage. The smaller you find them, the easier it is to get rid of them.