Project Overview

Reports

Commodities

• Nuts: pecans

Target Pests

• Target Pests: other

Practices

• Pest Management: behavioral control, biological control

• Production Systems: agroecosystems

The United States is the leading producer of pecans, a native nut crop grown commercially in 15 states. Among these states, Georgia produces nearly one-third of the US pecan crop, valued at close to $500 million. Pecan has been an important cash crop for growers until recently, when the price of nuts has fallen despite rising input costs. In this situation, growers cannot afford to lose their production to insect pests or diseases, which must be managed efficiently and sustainably.  

Among the insect pests that chronically damage pecan crops, Prionus root borers are major root-feeding pests that can destroy older pecan trees by compromising their root systems. There are three species of Prionus root borers (Prionus imbricornis, P. laticollis, and P. pocularis) found in pecan across the southern US. Whereas, another species, P. californicus, is dominant in the western US, and is reported to cause serious damage to cherry, hop, and apple. In addition to pecan, Prionus root borers infest blueberry crops in North Carolina.   

Prionus root borer larvae remain in the subsurface and feed on the root system, which compromises the stability and nutrient uptake of pecan trees. Therefore, trees become weak, unproductive and fall over following any wind or hurricane events. Every year, growers in Georgia and nearby states such as Alabama lose mature, older trees from storm systems, which is partly due to the damaged root systems of pecan trees from Prionus beetle. The adult beetles do not feed on the plant, are short-lived, and inactive during the day. The control options for Prionus in pecan orchards are limited. A few years ago, growers used Chlorpyriphos around the base of the tree to kill emerging adults, but it is no longer available and requires alternative solutions to manage this important pecan pest. Pheromone traps are now extensively used to monitor and mass trapping of male beetles. However, mass trapping of males seems not to result in significant population decline. The mated females will lay eggs and keep building the population up, even in the presence of a limited number of males. Therefore, trapping and targeting the female beetles along with the males would be a more practical strategy to reduce beetle populations.

Since the Prionus beetle adults are nocturnal, the use of light traps could prove effective in capturing both male and female beetles. Previous research indicates that using light traps in combination with pheromone lures increases the capture of adult beetles. However, the light source, wavelength, etc., could play a significant role in improving trapping efficiency. Moreover, the use of a light trap alone has not been evaluated under field conditions. The second approach for killing the Prionus root borer adults is the use of entomopathogenic fungi (EPF). Our preliminary laboratory experiments found that commercially available EPF strains can cause mortality of adult prionus beetles. Application of EPF inoculum to the soil around the base of the tree at regular intervals during the adult emergence period could lead to high infection rates among adults following contact with EPF spores and result in insect death. Use of EPF could also result in auto-dissemination, in which males carry EPF spores and disseminate them to the female during mating, and thereby mating may result in the death of both male and female adults.

We anticipate that these two new methods of controlling Prionus beetles will be successful in significantly reducing the insect population and can be integrated with insecticide applications, leading to an integrated pest management solution for Prionus rooter borers in pecan and other crops.