Southwestern Region

FOREST HEALTH: Sawfly Defoliation Activity in the Region

We have had many different insects reach outbreak population status as the drought conditions in the Southwest continue. The latest are sawflies, relatives of wasps and bees, whose caterpillars defoliate conifers. These insects generally have only one generation per year. Five species of sawflies feed on ponderosa pine in Arizona.

Heavy sawfly defoliation has been noted east of Heber, Arizona in spring 2007. Sawfly infestations can cause temporary tree growth loss and sometimes tree mortality, especially when the trees are already stressed or the defoliation continues a second year.

Outbreaks generally last only a year or two and subside due to natural causes. Surviving trees will completely recover after several years.

Homeowners are encouraged to keep their trees healthy by deep infrequent watering during dry spells. Caterpillars can also be removed from the trees with a strong jet of water.

Visit the Pine Sawflies page of our electronic Field Guide for more information on these insects.

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