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Sawfly on evergreens

Juniper sawfly

Caterpillar-like, sawfly larvae are common summertime pests. Several species feed on the young needles of evergreen trees, which poses a serious threat to the plant's health. To prevent extensive defoliation, apply sprays where sawfly larvae populations are high.

Web-spinning sawfly in spruce

Sawfly larvae are similar in appearance to a caterpillar. The adult sawfly is a stingless wasp that causes no harm.

Larvae typically feed for two to three weeks, primarily in early May. Sawfly larvae also may be seen on Ponderosa pine in March, and on other pines in late August. gardeners often observe feeding damage after the larvae have gone, and sprays have no value at this point.

Sawfly, Neodiprion ventralis, larvae feeding on needles

A light population may not cause serious damage, but moderate to heavy populations can cause serious defoliation, which significantly impacts tree health. The aim of control is to stop defoliation before it becomes too extensive. When sawfly larvae are present in high numbers, sprays are justified to protect tree health.

Mating pair of juniper sawfly

To control sawfly larvae, spray infested evergreens with insecticides such as Orthene (acephate), Permethrin or Sevin. Even though the larvae are caterpillar-like, the natural insecticide Bt, or Bacillus thuringiensis, isn't effective on larvae or adult sawflies.

Bull pine sawfly, Zadiprion townsendi, larvae

Apply the spray at the beginning of an attack, while the sawfly larvae are young. Complete coverage is important for control. Sawflies may be seen on one tree and not others nearby. Spray ONLY the infested trees, but occasionally examine other trees for possible additional outbreaks. Sawflies are more prone to attack single landscape trees that are planted out in the open, rather than trees in a forest-like setting.

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Updated Friday, April 19, 2013