I am getting several reports from consultants, growers, and processors of high percentages of Navel Orange Worm (NOW) damage on the late harvested almond varieties. These reports have varied, but in all cases, damage has exceeded the targeted rejection rate of 2%. This has caught many people off guard.
So, why did this occur? The cooler spring weather experienced meant a delayed hullsplit and harvest. This delay was most pronounced within Monterey and Fritz, which were about two to three weeks behind the “normal” harvesting time. Harvest was delayed further by the early-October rain event. This increased “hang time” of the almonds within the tree provided the opportunity for more NOW damage. These varieties were exposed to the 2nd flight (during hullsplit), the 3rd flight (during harvest and drying), and 4th flight (during drying) of NOW which led to a greater rate of infestation. Since most growers applied a single NOW spray timed at 5% of Nonpareil hullsplit, these varieties were not only exposed to high populations of NOW, but were left without any type of chemical protection. A second NOW spray timed for the hullsplit of the Monterey and Fritz would have provided effective NOW control. Egg trap monitoring would have indicated the need to spray at this time. Keep in mind that NOW develops more quickly on new crop than on mummies.
It is also important to note that almonds are still susceptible to NOW infestation even after shaking. Increased time on the ground from poor drying conditions have also played a part in increasing the levels of infestation. Shook almonds were also exposed to the 3rd flight of NOW as well as a partially emerged 4th flight, and may partly explain the high number of young larvae within the hulls and kernels.
Earlier this year, Walt Bentley, UC IPM Specialist, suggested the possibility that the timings of the NOW flights may coincide with the hullsplit and harvest of the later varieties. This was also brought up in question answer at the CSJV summer almond meeting. He encouraged growers to actively monitor their fields to determine when the increase in NOW egg deposition was occurring in order to apply properly timed sprays. I have to tip my hat to Walt, as I felt that he nailed the prediction of this event and did his best in disseminating the information to the public. Walt – we are going to miss you upon your retirement!