Take Action if Tree Insect Pests Detected

Kali Zammit, Schmit, Rene G.  |  8/7/2013 12:28:03 AM

Three insect pests that can be quite troublesome for trees during the late summer months include bagworms, fall web worms and pine sawfly caterpillars.

Bagworms are a common pest to Louisiana conifers especially on cedars, cypress, arborvitae and junipers. They often go unnoticed due to their hanging, spindle shaped, silk-spun bags that look like miniature plant cones. The earliest signs of bagworm injury are brown or stressed needles at the tip of branches. A heavy infestation can completely defoliate a conifer plant in a short period of time. Bagworms can be controlled by either picking off the bags (on smaller size plants) and destroying them or spraying with Orthene, Acephate, Spinosad, Carbaryl (Sevin) or BT insecticides. It is important to spray in late evening or at dusk during the cooler time of day when the bagworms are actively feeding. Keep in mind that more than one spray application may be necessary to accomplish a complete and effective control.

Fall web worms infest many types of trees, in particular pecan, sweet gum, cypress and river birch. Fall web worms produce a new generation every thirty days and will remain throughout the summer until either the tree runs out of foliage or the weather cools. These caterpillars will feed continuously and will gradually enlarge their webs to encase more foliage as the larvae increase in size. Control for fall webworms can be accomplished using any one of the same insecticides as recommended for the control of bagworms. However, 2 to 3 ounces of a liquid soap should be added to the spray to assure good contact with the caterpillars. The soap allows the insecticide to cling to the caterpillars and to the webbing therefore reducing the number of sprays needed to manage the population. Again, spray in late evening and be sure to always follow label directions.

The Pine Sawfly caterpillar attacks primarily pine trees, specifically larger, mature trees. The pine sawfly is actually a wasp but it is the emergence of a new generation of larvae that causes tree damage from feeding on the pine needles. Early damage can be noticed by reddish-brown straw-like remains of needles that typically begin at the top of the tree and graduates downward. As the feeding becomes more intense, various branches throughout the tree take on a "bottle brush" appearance from needles damaged by sawflies. Sawfly colonies can consist of a few to more than a hundred caterpillars feeding and it is not uncommon for some to drop to the ground. Sawfly caterpillars can be easily distinguished by a U formation they exhibit from raising their head and abdomen at the same time. Often a truck lift is needed for applying insecticide in order to reach the upper level of the tree and therefore control for pine sawflies should be conducted only by a professional such as a tree company or pest control operator.

Although these important insect pests will remain active well into early fall, doesn’t mean your trees are affected. Homeowners with hardwood and conifer trees in the home landscape should however, continue a vigilance for quick action to reduce damage or death to plantings should an infestation be detected.

Rene’ Schmit is the LSU AgCenter county Agent for St. Charles Parish and can be reached at 985-785-4473.

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