Pecan Root Borer Control

Summary

A control method for tilehorned prionus and broadnecked root borers in commercial pecan orchards has been developed combining pheromone-baited traps and chemical control.

Situation

The prionus root borers of pecan, commonly called the tilehorned prionus and the broadnecked root borer, feed on the larger roots of the tree as larvae causing the roots to weaken and break when the feeding site becomes larger than the root. Feeding damage also reduces the uptake of water by the tree and gradually reduces tree production and eventually kills the tree directly or severely weakens the 'anchoring' of the tree in the soil and the tree topples in high winds. The injured trees are then typically removed and replaced by a new tree. New trees usually come into production 10-12 years after planting and are planted at a density of 12 trees per acre. Removal of one tree per acre results in an 8% reduction in pecan production for 10-12 years. To add insult to injury, the subterranean larvae tunnel through the soil whenever they outgrow the root they are feeding upon. These migrating larvae often encounter the underground irrigation lines, mistake the lines for the next root, and chew large gouge-like wounds in the lines. The grower then has to excavate the line until the damaged line is found and repair the system at considerable expense. Pecan orchards with high infestations of the root borers are widespread across Georgia and have been trapped in well-managed orchards from Mendes to Perry to Cordele to Leesburg to Albany and east to Tifton, Fitzgerald and Waycross.

Response

In 2009, the sex pheromone that the female prionus beetle releases to attract males as mates was found to be highly attractive to several species of prionus root borers including the two species on Georgia pecan. In the impending period, the pheromone was synthesized, mass produced and became commercially available for use. Trapping methods were developed in many horticultural crops across the USA where the root borers are pests. The pheromone was developed for use in pecan orchards through research at the Coastal Plain Experiment Station in cooperation with commercial Georgia pecan growers. The pheromone-baited traps attract beetles from as far as 800 ft from the trap and during peak beetle emergence one trap has caught over 400 beetles per week. These results indicate that the pheromone-baited traps may offer a method for beetle control. Collecting data in 2011, 2012 and 2013 found that the pheromone-baited traps are highly effective in delineating the emergence pattern of the adult beetles across Georgia and beetles emerge about a week early in Tifton-Albany area than in Perry. Adult emergence begins in late April extends through July and some beetles were captured in August. During 2012, a “male trap-out” technique was tested at Cordele indicating that surrounding a 60 acre orchard with 30 pheromone-baited traps significantly reduced the trap catch in the center of the orchard. During 2013, a “mating confusion technique” was tested at Perry indicating that live females did not attract males when a matrix of pheromone-baited traps was set out in the orchard at a density of 1 trap per 2 acres. Observation of the adult behavior during the daytime found that both sexes split their time between running across the orchard floor and digging in the soil and leaf litter. Females also spend a considerable portion of the time digging oviposition sites in the soil at the base of the trees and lay eggs. Male beetles also are good flyers. A chemical control was developed at the Coastal Plain Experiment Station to exploit this behavior where the soil around the base of each tree is treated with chlorpyrifos, a long residual organophosphate insecticide. The efficacy of the treatment was 93% against the adult male beetles. Insufficient female beetles were available for an insecticide efficacy trial. Males can be trapped out by surround each 60 acre block with 30 equally-spaced, pheromone-baited traps at a cost for materials of $13/acre in the first season and $3/acre in subsequent seasons. Free hanging pheromone lures at a density of 1 lure per 2 acres of pecans to prevent the males from finding females after the emerge by masking the pheromone that is naturally released by the females with a cloud of pheromone has a materials cost of $3/acre. Treating the soil around the base of each tree with chlorpyrifos to kill any females that become mated and attempt to lay eggs in the orchard has a materials cost $4/acre.

Impact

The research provides an effective control method for a pest problem that could only be controlled by removing affected pecan trees. The new method is less expensive than removing trees and replanting trees. Most Georgia pecan growers with a significant infestation are currently cooperating in the research effort. The on-farm research was carried out Perry, Cordele, Leesburg, Albany, Fitzgerald, Mendes, Waycross and Reidsville with the growers supplying funds for traps, and orchards for field trials. The research plots has to be large since the pheromone attracts beetles from a long distance and subsequently the trial plots usually encompass the entire infested area on the farms. So far the “male trap-out”, “mating confusion” and “trunk sprays” have been shown to be effective in single orchard trials and trunk sprays where also combined with pheromone trapping at three locations in an integrated approach for control of the root borers. The measurement of the effects of control on actual production will take several seasons of research. Continued research is planned for 2014 to test integration of the three methods at farms with high infestation levels.

State Issue

Agricultural Profitability and Sustainability

Details

• Year: 2013
• Geographic Scope: National
• County: Tift
• Program Areas:
  • Agriculture & Natural Resources