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Roseslug Sawfly (06/16/16)

Larvae of the roseslug sawfly are being observed on roses in Stutsman County (Source: Alicia Harstad, NDSU Ag Extension Agent, Stutsman County).

Roseslug Sawfly

Larvae of the roseslug sawfly are being observed on roses in Stutsman County (Source: Alicia Harstad, NDSU Ag Extension Agent, Stutsman County). These insects are not slugs at all, but secrete a slimy substance over their body which makes them look like slugs. Larvae are light green and about ¾ inch long. Larvae cause the damage to roses by chewing on the foliage, often feeding between the leaf veins. Light to moderate defoliation is essentially cosmetic; however, heavy defoliation can stress the rose plant and make them more susceptible to diseases and other insect pests.

There is one generation per year. The adult is a sawfly wasp, and emerges in spring to lay eggs on underside of roses. Larvae hatch from egg after several weeks and feed on leaves for about a month. Then, mature larvae drop to the ground to pupate.

It is good to check roses early for any signs of infestation. If infestation is low, larvae can be removed by hand or by spraying with a strong jet of water on upper and lower surfaces of leaves. Parasitic wasps, birds and fungal disease are common and often will reduce population of sawflies without pesticides. In most situations, insecticides are not necessary for control of roseslug sawflies, especially when the rose plant is healthy and sawflies are removed early in plant development.

If insecticides become necessary as the last resort, the following active ingredients can be used to control sawfly: acephate, bifenthrin, carbaryl, cyfluthrin, lambda-cyhalothrin, malathion and permethrin. Biorational (organic) pesticides include azadirachtin (neem oil), insecticidal soaps, pyrethrin and spinosad. Bacillus thuringiensis (Bt) will not control roseslug sawfly larvae (Bt controls only Lepidopteran larvae of moths and butterflies).

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Janet J. Knodel

Extension Entomologist

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