During my time as the pecan IPM specialist for Texas A&M AgriLife Extension, I have written several articles for Pecan South on pecan weevil management, but for this month instead of a management focus, I would like to address the potential spread of pecan weevil to new areas. I am probably addressing the wrong audience for this topic for I feel (or at least I hope) that anyone involved in pecan production knows about the threat of pecan weevil. But the general public does not. And it is the general public that really needs to understand the potential problem of unintentionally moving this insect to new areas.
When it comes to discussions on the most important insect pest, both the pecan nut casebearer and pecan weevil are considered the most important by most producers, but back in 1972, representatives of eight states—made up of entomologists and administrators—agreed that the pecan weevil was the number one pecan insect pest at a Pecan Insects Conference in Biloxi, Mississippi.
(Texas A&M was represented by Horace Van Cleave and Marvin Harris. The program formed at this meeting has been renewed and expanded many times and is still active to this day. Much of what we know and use in current management practices for pecan weevil resulted from the objective information provided by these pecan scientists).
Unlike pecan nut casebearer that infests pecans primarily during the early season, the pecan weevil as a late season pest infests and damages harvestable nuts, which results in a direct loss to a producer.
Pecan weevil is native to North America and has been collected from all 13 or 14 North American hickory species. However, its distribution’s details are only known for those populations associated with pecan. The attached map of pecan weevil distribution in the Southeast does not take into account its distribution on hickory and pecan in northern states.
According to research by Lester P. Gibson in 1968, the general distribution of pecan weevil is “west from New York to Iowa and south to Oklahoma, Texas and Georgia.” More recent studies also show that pecan weevil can infest Persian walnut, and thus, also poses a threat to that industry as well as provides a new means to spread infested nuts.
In order to combat the spread of pecan weevil, each individual producer will have to manage pecan weevils if present in the orchard. I have seen an orchard where no management was applied for several years, and I would guess that 95 percent of the pecans had signs of pecan weevil. Management of pecan weevil requires at least two late season insecticides, which indirectly causes problems with secondary pests and adds additional production costs.
For pecan producing states, there is potential to spread from infested counties to non-infested. In Texas, pecan weevil has been recorded in more than 130 of its 254 counties with the most recent detections from the counties shown in blue in the Texas map—Hays County in 2014 (San Marcos) and Comal County in 2015 (New Braunfels). I have also had a verbal report from Lynn County for 2016 (shown in black). It is unclear if these new detections were the result of man-assisted movement or not.
These verified infestations should be an alarm clock moment for the Texas pecan industry because they show, for the first time, that the Guadalupe River watershed is now at risk of being slowly but surely infested. Close inspection of a topographic map reveals there are no natural barriers to prevent further spread because these newly infested areas are adjacent to streams lined with wild, native and improved pecans that flow all the way to the Gulf of Mexico.
But this isn’t just a Texas problem; it’s an industry problem. I hear all too often of new detections in New Mexico and fear for its potential to spread even farther west into Arizona and California.
One method to help prevent this westward spread is through quarantines. Texas currently has a pecan weevil quarantine for all counties except its five most western counties. This quarantine includes all in-shell pecans as well as cracked pecans or any pecan shipments containing shell pieces. Anyone in Texas in the quarantine area that sells or ships pecans to New Mexico, Arizona or California must meet quarantine treatment requirements.
Quarantines are effective on the commercial side, but what about personal vehicle movement?
A case in point here is where pecan weevil was detected for the first time in Tularosa, Otero County, New Mexico during the winter of 1969-1970. Although the infestation was eventually eradicated, the source of this infestation remains unclear. However, one of the residents in the infestation area recalled having a grocery sack of “bad pecans” that were collected from the native range of pecan weevil. This resident disposed of this sack of “bad pecans” in their backyard during the early 1960s.
In looking at the accompanying picture of east New Mexico and West Texas and the reported infestations in New Mexico, these have to be the result of man-assisted movement. These pop-up infestations are costly for the New Mexico Department of Agriculture to try to eradicate because they can take years of treatments, and even then, remain a problem for the pecan industry.
I don’t have a solution to this problem, but one way I try to address it is by talking about the pecan weevil at all my county meetings, regardless if the county has weevils or not. I feel that communication with producers and the general public is important in getting the message out. If all those involved in the pecan industry began to communicate with the general public about this important issue, then we could possibly take a step in the right direction and stop the further spread of pecan weevil.