Leafminer, shuckworm pests target New Mexico pecans

New Mexico pecan growers and consultants are on alert after a new leafminer species was found last year in the state along with the reappearance of the hickory shuckworm.

Carol Sutherland, New Mexico State Entomologist, late last summer tentatively identified the critters as the pecan serpentine leafminer, Stigmella juglandifoliella, and hickory shuckworm, Cydia caryana.

“The pecan serpentine leafminer creates winding tunnels inside pecan leaflets which can cause tattered foliage when the mines dry and break apart in the wind,” Sutherland told a 600-plus crowd at the 45th annual Western Pecan Growers Conference in Las Cruces, N.M., in March.

“The pecan serpentine leafminer will likely be a very minor pest in New Mexico pecans – a spotty critter found today, perhaps not again for several years, or found on another farm down the road,” said Sutherland who also serves as New Mexico State University Extension entomologist.

The insect was found in two New Mexico commercial pecan production areas; first in the Roswell area in Chaves County on a late-season flush of new leaves. The second find was in sparse foliage in small caliper trees transplanted in early 2010 in the Mesilla Valley in Doña Ana County.

Healthy, mature trees can lose a few leaves but are easily replaced by vast reserves. The pecan leafminer is an occasional but sometimes serious pest in the southeastern U.S. pecan belt.

At least five species of leafmining caterpillars from three families in the Micro-Lepidoptera family attack pecan. The wingspan on the tiny moths are 10 millimeters or less; smaller in width than a thumbnail.

“Leafminers are likely controlled by weather, climate events, plus natural enemies especially in ‘wild’ stands or backyard trees,” says Sutherland. “In commercial orchards, cultural practices and insecticide treatments for other key pecan pests can reduce leafminer numbers or keep the insect at low levels.”

Many chemicals with numerous active ingredients registered in New Mexico are available for pecan serpentine leafminer control. Unknown is whether the insect has been in New Mexico for awhile or if the bug was transplanted from elsewhere. If the leafminer has been around, Sutherland says insecticide treatments for aphids and the pecan nut casebearer may have suppressed pecan leafminer numbers.

More than one generation of pecan leafminers are likely in New Mexico annually. Leafminer moths have a complete metamorphosis: egg, larva, pupa, and adult stages.

“I encourage producers and consultants to spend more time looking for mines and foliage irregularities,” Sutherland said. “If mines are found, determine how common and widespread the mines are and whether economic damage is occurring before making a decision to treat.”

Mines cannot heal and insecticides cannot repair damaged foliage. Pheromone traps do not exist for the tiny leafminer. Unknown is when insect flight activity peaks.