OVERTON– East Texas pinewood forest landowners are seeing heavy infestations of sawflies again.
The reported infestations are not as numerous as last summer and fall, the degree of damage is still worse than average, according to Dr. Eric Taylor, Texas Agricultural Extension Service forestry specialist.
“As with last year’s infestations, the greater than normal numbers are most likely due to the extremely mild winter we had,” Taylor said.
Sawflies, which are actually non-stinging wasps, have long been known to attack East Texas pine trees. Depending on the species of sawfly, the larvae either strip most or all the pine needles off a tree or eat the soft outer tissue of the needles, leaving them to die and turn brown. As they feed, their excrement, which bears a resemblance to green, ground up pine needles, rains to the forest floor.
During an average growing year, an infestation by either species spells reduced growth and vigor. The tree usually recovers the following spring as it grows new needles. The last few years have been far from average for East Texas pine trees, however. Two hot, dry summers out of the last three have stressed many pines to the limit of survival.
With levels of stored nutrient reserves at critical levels, many pine trees may not be able to grow new needles this year. Or, if they did, the energy expenditure will reduce vigor and may make them susceptible to attack by the southern pine beetle.
Three species of sawfly are common to East Texas. All three are easily identified. The older larva of the black headed pine sawfly is about 1 inch long with an olive green body and a glossy black head. It has two black stripes that run along the length of its body, and rows of black spots on each side. This species of sawfly eats the entire pine tree needle, leaving only a stub. In large numbers, it commonly defoliates 90 percent or more of a pine tree’s needles.
A larva of the loblolly pine sawfly is also about 1 inch long but with a dull green body having black stripes along each side. It will often have two lighter stripes below the black ones, but is most easily identified by its reddish brown head. This species strips off the outer layer of pine tree needles, leaving them to turn a reddish brown. Older larvae may consume the entire needle, leaving only stubs.
The redheaded pine sawfly may be as long as 1-1/4 inches. Its body is yellow-white with six rows of black spots. It can easily be recognized by its bright red head. It eats all of the pine needle as does the blackhead pine sawfly.
Pictures of all three species of sawfly can be found on Taylor’s Forestry Answers website. (http://forestryanswers.tamu.edu) From the main page, click on the button labeled “Forest Pests.”
If their trees are infested, there’s little forest landowners can do but wait and see if their trees recover. Although a number of pesticides will effectively kill sawflies in the larval stage, the expense of treating large acreages is prohibitive, Taylor said.
Yards with only one or a few favorite trees infested can be treated using a product labeled for home landscape use such as Dursban or orthene.
“If there are sensitive plants or outdoor pets then a product containing orthene may be a better choice,” Taylor said.
The best bet for control is to spray the whole tree from trunk to crown. Obviously, for a tall tree, this isn’t practical, or safe, without special equipment. An option is to spray as high up the trunk as possible.
“The larvae travel up and down the trunk and this will kill a large percentage of them,” Taylor said, adding that a better option yet is to call a tree service.
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