We’re heading towards the second codling moth biofix. This biofix is set when trap numbers increase, approximately 800 to 1300 DD after the first biofix. Use the following decision table to determine whether treatment is necessary: http://ipm.ucanr.edu/PMG/r881300211.html
Monitor spider mites weekly through August. Examine 10 leaflets from 10 trees (5 should be from higher branches). If more than half the leaflets with spider mites don’t also have predators (predaceous mites and/or sixspotted thrips), this is a cause for concern. Treatment guidelines based on spider mite and predator presence can be found at: http://ipm.ucanr.edu/PMG/r881400111.html
Codling moth third flight occurs in late July to early August (on average, 1,100 DD after the second biofix). Check traps to pinpoint the third flight biofix. Treatment decisions are based on a combination of factors including previous treatments, number of nuts infested in the previous generation, trap catches, and the ability to harvest early.
If sprays are going to be applied for eggs from the second generation, apply at 300 Degree Days (DD) after the third biofix (200-250 DD if insect growth regulators are used). More details: http://ipm.ucanr.edu/PMG/r881300211.html
Continue weekly monitoring for husk fly and spider mites. See trapping and monitoring details above.
Take July leaf samples to assess nitrogen, potassium, and zinc, as well as boron toxicity, depending on your circumstances. Sample 1-2 terminal leaflets from at least 29 trees, each at least 100 feet apart, on the same rootstock scattered throughout the orchard.
Be careful when timing ethephon applications for advancing walnut harvest this year. A late bloom and leafout may delay application timing compared to the last couple years. The most reliable way to avoid damage is to examine nuts for the packing tissue brown (PTB) stage. Do not treat earlier than 100% PTB. For more on sampling for PTB and safely applying ethephon, see: http://sacvalleyorchards.com/walnuts/horticulture