Tiny Tarnished Plant Bugs Cause Big Problems for Pine Seedlings

AUBURN, Ala.—Alabama Agricultural Experiment Station research recently unraveled the mystery of an increase in malformation of pine seedlings in Southern nurseries. The culprit is an insect commonly called tarnished plant bug (scientific name Lygus lineolaris). Feedings by this insect causes seedlings to form multiple shoots, called "bushy top." Seedlings with this damage are often culled from the crop, costing nursery managers in the Southeast thousands of dollars annually.

Bushy topped pine seedlings were first reported on loblolly pine in a nursery in Coosa Pines in 1982. Subsequently, seedling injury has been reported as far south as central Florida and as far north as Virginia. Pine species affected include loblolly, slash, longleaf, Virginia, sand and Scots. Initially, damage was attributed to herbicide use, a fungus, thrips, a virus, a nutrient deficiency, a fertilizer burn and even air pollution.

Auburn researchers were the first to suspect that loblolly southern pines were being injured by tarnished plant bugs. As a result, greenhouse tests were conducted by caging adult tarnished plant bugs with young pine seedlings. This demonstrated that feeding on the terminals of young loblolly pine seedlings results in malformed terminals and the development of multiple shoots. Tarnished plant bugs are very mobile and, by the time injury symptoms are visible, the insect is gone. Within a few days the insects can move onto nursery beds, feed and exit to adjacent areas that contain alternative hosts. These insects usually feed at night or early morning. The combination of these factors helps to explain the difficulty in associating tarnished plant bugs with bushy topped seedlings.

In 1987, the Auburn University Southern Forest Nursery Management Cooperative installed monitoring studies at five nurseries throughout the South. Seedling injury at all five nurseries was first apparent by the end of May and the first week of June. Twelve white traps (Rebell®) were placed throughout each nursery. The cumulative number of tarnished plant bugs caught per trap was determined for each nursery.

Although trapping can be useful in determining when to begin spraying insecticides to control the pest, it has a major limitation. For example, at the New Kent Nursery, no tarnished plant bugs were trapped through May 31. During the next two-day period, 2.5 per trap were caught. A spray program initiated after scouting on June 2 would have protected the crop only from future injuries, but substantial damage would already exist. If only four percent of a crop of 30 million seedlings is culled due to bushy tops, a loss of $36,000 could result. Therefore, nursery managers who previously have had their crops damaged by tarnished plant bugs usually spray prophylactically with an insecticide, such as ASANA XL®.

Instead of using traps, some nursery managers prefer to monitor known weed hosts each morning. If a single tarnished plant bug is found on host weeds during pine seedling germination, nursery managers often will spray with an insecticide. To reduce resident populations, some nursery managers attempt to control preferred weed hosts. In fact, a likely reason for the increase in tarnished plant bug damage to pine seedlings is due to changes in weed management practices, especially the curtailment of the use of mineral spirits for weed control. Mineral spirits has a strong petroleum odor and exhibits some contact insecticidal activity. The switch to more efficient diphenylether herbicides in the early 1980s coincides with the increased damage.

Now that Auburn research has made nursery managers aware of the cause of bushy topped seedlings, measures to control tarnished plant bugs are routinely taken, resulting in a dramatic drop in damage. In one nursery, the percentage of trees damaged has been reduced from 17 percent with no control measures to less than 1% with timely applications of insecticides.

-30-

News from:

Office of Ag Communications & Marketing

Auburn University College of Agriculture
Alabama Agricultural Experiment Station
3 Comer Hall, Auburn University
Auburn, AL 36849
334-844-4877 (PHONE) 334-844-5892 (FAX)

Contact Jamie Creamer, 334-844-2783 or jcreamer@auburn.edu
by David South

02/17/92