Pecan Weevil Emergence on The Rise - Aug. 14, 2024

With recent rains driving fruit development, pecan growers should be watching their orchards for signs of pecan weevil activity. What to look for, however, is a matter of timing. 

 

Pecan weevils primary cause 2 types of damage, depending on the stage of fruit development when the pests are active.

 

Nuts that are punctured and drop off the tree indicate weevils have fed on the kernel in the water stage of development (Fig. 1). This stage of development refers to a point at which the shell and kernel seed coat have reached their full size. Rarely, female weevils oviposit in pecans still in the water stage but when they do, larvae do not survive. The amount of this type of damage depends on weevil population density, time of emergence, and longevity of the weevils.

 

When shells harden later in the season, around dough stage in late August (Fig. 2), female weevils probe the nut to lay eggs. Shucks may adhere to the shell past normal harvest time when that happens. Damage is initiated by the larvae as they feed on the kernel (≈42 days). Such mature nuts typically do not drop from the tree while the larvae grow. Two to four larvae within each infested nut can easily destroy the entire kernel. Research has shown that individual weevils destroy an average of about one pecan every four days.

 

Female weevils can produce 30-54 eggs, therefore, with only 2 eggs/nut as many as 27 nuts can be affected from each female (Fig. 3). Oviposition has been observed as early as two days after emergence; however, the average preoviposition period is about 6.5 days. Egg-laying begins when nuts reach the dough stage – typically late August to early September.

 

However, this season tree phenology (timing of biological events) was accelerated due to early season warm temperatures, which has led to earlier than normal fruit development. Pecan nut development at the Cimarron Valley Research Station (Perkins, Ok), is about 2 weeks ahead of schedule. Therefore, recent rains across the state may have provided a trigger for weevil emergence and the potential for damage (Fig. 4 & 5) to occur earlier than normal. Weevils are being caught at the CVRS research station, consequently, decisions on the first weevil application will be made this week.

 

Circle traps (Fig. 6 & 7) are a useful tool for pecan weevil monitoring, providing good indications of weevil presence and abundance within an orchard. Weevil emergence can vary from location to location, and even within an orchard. Ideally, traps should be put out by mid to late July to account for any early weevil activity, such as we are experiencing currently.

 

For more information on pecan weevil control and other research-based orchard management practices, consult OSU Extension fact sheet 7079 - Biology and Control of the Pecan Weevil in Oklahoma and , 7190 - Monitoring Adult Weevil  Populations in Pecan and Fruit Trees in Oklahoma,  available online  and through all county Extension offices.