By Emily J. Symmes, UCCE Area IPM Advisor, Sacramento Valley
NOW management in the Sacramento Valley relies heavily on sanitation, early and rapid harvest, and hull split treatments when necessary to protect the new crop. Proper execution of these practices keeps NOW populations below damaging levels. This year we may face higher navel orangeworm pressure due to the dry winter that made sanitation more difficult while reducing natural overwintering mortality.
Warm spring temperatures led to earlier NOW egg biofix dates this year which will lead to earlier third generation egg laying as harvest approaches and the likelihood of a fourth generation before harvest is complete. May sprays, under discussion in other parts of the state, reduce NOW and PTB populations if timed properly but do not protect the maturing crop.
While May sprays targeting first generation NOW might seem like an attractive option if high populations going into hull split are anticipated, there are limitations to this strategy in the northern parts of the Central Valley. May sprays will reduce resident populations but will not protect the new crop when it becomes vulnerable to NOW infestation at hull split from resident or immigrant moths. May sprays may help in the southern Central Valley, where almond blocks tend to be much larger, resident NOW populations higher due to very low sanitation thresholds, and regional pressure greater due to proximity to other sources of infestation (i.e., pistachio orchards), but aren’t generally a great fit for the Sacramento Valley.
Applying May sprays for peach twig borer (PTB) and obtaining simultaneous control of NOW is also appealing. However, this is not a guarantee and will only occur if the life cycles of the two pests are synchronized and/or the material chosen has long residual impacts. Therefore, PTB should be treated only as necessary based on monitoring and threshold values (see http://www.ipm.ucdavis.edu/PMG/r3300211.html for information on PTB management). In addition, application of certain materials during spring disrupt natural enemies of webspinning spider mites and increase the need for miticide treatment. Given these considerations in the Sacramento Valley, hull split treatments provide maximum crop protection from NOW with minimal non-target and secondary pest impacts.
Proper timing of hull split treatments involves monitoring egg traps, using degree days, and crop phenology. If you choose to treat at hull split, and eggs are being laid on egg traps, time the spray to the initiation of hull split. If eggs are not being laid on egg traps when hull split begins, time the spray to an increase in egg-laying on traps or the predicted initiation of egg-laying according to degree day models, 1200 degree days after spring biofix.
Hull split initiation is when sound fruit in the tops of trees begin to split. At this time, the nuts at eye level will be less mature and will show only a deep furrow at the hull suture. Nuts in the top southwest quadrant of the tree split first. Blank nuts (usually 3 to 5%) will split 1 to 2 weeks ahead of sound nuts. Use a long-extension pole pruner to cut small branches from this top portion of five or six trees in the orchard to check whether hull split nuts are blank or sound.