Archive for Sunday, May 5, 2002

Protect pines from sawflies

May 5, 2002


Pine trees are an interesting and important focal point in any landscape. However, a pine tree with no needles becomes a focal point for the wrong reasons.

European Pine sawflies are starting to feed. If you had a problem with this insect in the past, check your pines for the beginning stages of damage before your evergreen is stripped of its green color.

The adult sawfly is an uninteresting orange or black flying insect. However, it is the juvenile or larval stage that is important. European pine sawfly larvae feed on the old needles of all species of pines grown in our area but prefer Scotch pines.

When these worms are small, they cannot consume a complete needle. Instead they rasp off the top layer of cells. This leaves individual needles brown and twisted. Look for this kind of damage to pinpoint where these sawfly larvae are feeding. Because the larvae are gregarious, a number of larvae will be found close together.

Only during the last developmental stages at the end of April and beginning of May when large larvae are feeding heavily do people notice extensive damage. Larvae move to the tips of needles and quickly consume them before moving onto the next needle. After defoliating an entire branch, they move on to the next one and begin eating.

Extensive feeding gives trees a barren look. Because this takes place before the new needles expand, the tree is rarely killed.

Once sawfly larvae have stopped feeding, normal needle growth begins. The tree may look "puffy" with terminal tufts of needles on the ends of bare branches.

A number of insecticides can be used for controlling feeding larvae including Orthene, cyfluthrin (Bayer Lawn and Garden Multi-Insect Killer), malathion and Sevin. Horticultural oils also are effective because of the soft skin of the sawfly larvae.

A possible drawback to these materials is that they are wide spectrum, meaning they kill not only the targeted pests but also nontarget organisms including beneficial predator and parasite insect species.

Therefore, try to concentrate your spray only to the infected areas. And, as always, read and follow label directions.

Bruce Chladny is horticulture agent at K-State Research and Extension-Douglas County. For more information, call him at 843-7058 from 8 a.m. to 5 p.m. weekdays.

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