Pecan Trees Damaged by the Hickory Shoot Curculio

Pecan samples brought to the University of Kentucky Entomology Laboratory in Princeton exhibited injury to new shoots and stems. These samples were collected by Darrell Simpson (Agriculture & Natural Resources Agent in Muhlenberg, KY) on behalf of a grower. The damage consisted of darkened holes near the bases of several shoots (Figure 1), along with leaf flagging (Figure 2). Further inspection of the samples, showed tunnels in the stems that extended into the pith caused by a legless larva (Figure 3). The larva had a yellowish color with a dark brown head and was approximately 10 mm in length. The combination of all these factors identified the hickory shoot curculio (Conotrachelus Aratus, Coleoptera: Curculionidae) as the culprit. Acrobasis shoot borers (Acrobasis spp.) cause similar damage during spring, but larvae are larger and have a dark olive-green coloration when mature.

The hickory shoot curculio is an insect well distributed in the USA: from Massachusetts to Florida and from Texas to Kansas.  Damage by this insect is most common in the eastern USA; however, infestations can occasionally build up enough to warrant notice in the Midwest and south-central regions.  Damage is often sporadic year-to-year, but if an outbreak occurs, more than 50% of shoots can be affected, severely diminishing nut production. Pecan orchards near wooded areas containing hickory trees or wild pecan stands are more susceptible to infestation.

Figure 1. Holes on pecan shoots (Photo: Raul Villaneuva, UK)

Figure 2. Leaf flagging caused by hickory shoot borer (Photo: Raul Villanueva, UK)

Biology

Adults overwinter near host trees in leaf litter and brushy areas filled with debris. They emerge in spring (around mid-April) and migrate to tender, rapidly growing shoots where the females will feed and lay their eggs. Larvae will hatch and begin burrowing into shoots shortly afterward, creating a tunnel. When the hickory shoot curculio larva completes its development, it comes out of the tunnel (Figure 4) and drops to the ground where it pupates for 2 to 3 weeks. The adult weevil emerges from August to September, feeds for a little while, and finds a well-sheltered area to pass winter. This insect has only one generation per year.

Figure 3. Tunnel caused by hickory shoot borer in pecan. Larva is legless and with a brown head (Photo: Raul Villanueva, UK)

Figure 4. Hickory shoot borer emerging from pecan shoot (Photo: Raul Villanueva, UK)

Management

Cultural controls are the most effective management tools when populations are low and infestations sporadic. Cultural controls include eliminating brush and debris to limit hibernation sites around trees, collecting all damaged tree shoots from the ground, pruning affected parts, and burning infested shoots outside the orchard. Establishing new plantings away from infested woodlots also helps but is often impractical for homeowners and smaller growers.

Chemical control is usually not warranted, unless there is a consistent history of this pest in an orchard. Preventative sprays to control adults before they lay their eggs can be done starting in mid-late April or early May when shoots are ¼ to 1 inch long. Insecticide treatments after the larvae have entered the shoots is ineffective.

More Information

 

Raul T. Villanueva, Extension Entomologist and Daniel Becker, Extension Associate for Vegetables/Fruit

 

 

Posted in Nut Crops