We are well past bloom in apricots with set and increasing fruit size observed this week in Highland. In years when we have abundant stone fruit we often find tree fruit growers and scouts bringing to us injured fruit with Plum Curculio larva, (PC) Conotrachelus nenuphar (Herbst). The cause in most every case was a delay in PC management.
Many growers wait to manage PC on apricots until petal fall of apple. This delayed management of PC in apricot, especially in a year like this with high temperatures bringing on adult emergence into orchards during apple bloom, will likely allow PC injury in apricot if left unprotected.
Fruit injury by egg laying adult PC females is dependent on timing of emergence, conditioned by temperature and coupled with fruit size. Tree fruit such as apricot, pear, cherry, plum and apple that mature >5 mm in diameter are susceptible to egg-laying by this pest. Apricot will likely be susceptible by weeks end. Night-time temperatures will be steadily increasing and showers are predicted Monday night (11 May) to increase relative humidity. Ideal conditions for PC to begin their reproductive cycle.
As the overwintering adults are hidden in ground litter and soil, mean temperatures above 60°F or maximum temperatures above 75°F prompt the adults to emerge and become more active. Continued emergence of PC adults will last for several weeks, yet in some years 40-60% of the total emergence may occur on a single day.
For those of you who want to see the ‘whites of their eyes’ before firing, check daily for PC activity in untreated sentinel apricot or cherry along a wooded edge to watch for the first sting. Unless a cold front moves in to slow PC movement into orchards, it will be time to begin PC management after the first sting is sighted.