The phenology of fourth instar plum curculio (Conotrachelus nenuphar) emergence in Michigan tart cherry and apple orchards with implications for managing the pest in soil

Increasing legal restrictions on organophosphate use in stone and pome fruit orchards has stimulated the development of new methods to manage the northern strain of the pest plum curculio, especially those taking maximum residue limit concerns into account. Residue-free fungi or nematode agents have been successfully used to kill the fourth instar of the pest as it attempts to pupate in the soil. However, the efficacy of these living biological agents is quickly degraded after orchard application so precise phenological models of pest activity are needed for effective management. Existing models complement springtime organophosphate use against pest oviposition; newer, summertime models are needed to target the pest before pupation. Furthermore, existing phenological models were developed for apple fruit but cherry are also attacked by the pest.

Two hundred Montmorency tart cherry fruit at four sites in southwest Michigan were deliberately exposed to female plum curculio in spring 2012, and the fruit, with larvae inside, developed on the trees while being individually protected in mesh bags. A similar experiment was conducted using Honeycrisp apple fruit in laboratory conditions after field apples were unable to sustain a sufficient curculio population. Time from egg to fourth instar-drop out in cherries in May weather conditions ranged from 16 to 45 days (375 base 10°C Degree Days accumulated), while in apples in September weather conditions it ranged from 25 to 45 days at time of writing (255 base 10°C Degree Days accumulated). Analysis of larval development and its implications for pesticide application are discussed.