Pecan Weevil (Coleoptera: Curculionidae) Emergence in a Range of Soil Types

Abstract

The pecan weevil, Curculio caryae (Horn), can injure pecan from kernel initiation in August until dehiscence of the involucre 2-3 mo later. Prevention of injury requires killing adults after they emerge from soil cells but before they oviposit within developing nuts. The adult emergence period is typically from mid-August to late September, but a portion of the population can be delayed in emerging because of drought hardened soils. Emergence was delayed in this study when soil penetrability was >65 kg/cm2. Soil penetrability as a function of percent soil moisture, clay, and sand can be predicted by the following equation: y = 137.713−8.965 x 1+3.463 x 2−1.190 x 3. Changes in soil penetrability caused by rainfall can be calculated by first determining the change in percent soil moisture as a function of percent soil moisture before rainfall, rainfall (centimeter), and percent sand: y = −18.358−0.607 x 1+0.458 x 2+2.342 x 3 and then solving the previous equation with the new value to update the status of pecan weevil emergence. These findings can be combined with data on soils and new weather monitoring technologies like Doppler radar to predict weevil emergence status initially and then update that status across wide regions on a near real-time basis to aid in making decisions with regard to pecan weevil management. These predictions would be based on county-wide rainfall data and growers would need to take into account their own irrigation programs before making any decision regarding pecan weevil control.