Evaluate Navel Orangeworm and Peach Twig Borer populations. If the next generations come prior to hullsplit they will go back to mummy nuts and shoots respectively. Generations can be predicted using your biofix and Degree Day models. Back up degree-day predictions by checking traps. Many signs indicate this will be another high NOW pressure year in some orchards. Check out here on options for aggressive management of NOW.
Monitor for mites weekly in the orchard’s hot spots. Consider the presence of predators (sixspotted thrips and predator mites, in addition to the presence of mites, when making treatment decisions). UC IPM guidelines indicate it’s acceptable to avoid treating until about 50% of leaves have mites if predators are present, about 30% of leaves if predators are not present. Expand monitoring to the whole orchard after July 1. For more on monitoring and treatment, see the easy-to-follow decision tree and more details here.
Survey ant colony concentration on the orchard floor 2 to 3 days after irrigation, counting active colonies in five 1,000 square foot areas (roughly a 5 x 6 tree rectangle). Confirm they are the undesirable (protein feeding) pavement or southern fire ants, not the harmless pyramid ants with helpful photos here. Estimate potential harvest damage using the table here and proceed based on your damage tolerance.
Apply 30% of your total nitrogen budget in early June to match the timing of tree demand. See here for more on rate and timing of nitrogen applications. If the block has a history of hull rot, don’t apply nitrogen (N) in June. The last N application in those blocks should be in May.
Ground squirrels switch from eating green vegetation to seeds and grains in late May. This means that June is the beginning of the window in which they will eat baited rodenticides. Test bait acceptance before use of rodenticide to avoid toxin shyness. For more on ground squirrel management, see here.
Manage young tree irrigation carefully as summer heats up, especially with potted trees, to make sure water is getting to the rootzone. For more on dealing with the challenge of irrigating potted trees, see here.
Get ready for hull split. UC models estimate hull split starting as early as July 4th this year for Nonpareil at some locations in the Sacramento Valley. To predict hull split using data from you nearest CIMIS station, visit here.
Regulated Deficit Irrigation (RDI) promotes earlier, more even hull split and reduces hull rot. This tightening of hull split may be an especially useful tool this year, given the prolonged bloom. Beginning at hull split initiation, induce moderate water stress by keeping mid-day stem water potential between -14 to -18 bars using a pressure chamber during hull split. Roughly the same effect can be achieved by shortening normal irrigation time by 50% for the first two weeks of hull split. Then catch up the last two weeks before harvest by providing full irrigation (matching ETc). For more, see the hull rot and irrigation article in this issue.
Take leaf samples in July to measure nutrient status. Adjust your nutrient management plan for the rest of the season based on July leaf sample results. For more on collecting samples and interpreting results, see the article on leaf sampling in this issue.
Watch for rust in young orchards. Prevent early defoliation that can negatively affect flower bud formation for next year. Defoliation at harvest can also delay nut drying. For more, see here.
Plan ahead to minimize dust at harvest. Consider steps like adjusting sweeper head heights, blower spout angles and fan speed. Find more suggestions here.
If you’re harvesting third or fourth leaf trees, keep an extra close eye on that shaker. Bark slips easily in young trees and can be an entry point for future infection, ultimately shortening the productive life of an orchard.
At harvest, collect nut samples for damage analysis. Gather at least 100 nuts per orchard after shaking, but before sweeping. Checking these samples immediately after Nonpareil harvest can inform NOW spray decisions for pollinizer varieties. If not checked immediately, freeze them for later. These samples will allow you to better understand damage results on your grade sheets and adapt IPM strategies for next year. Sampling and pest damage diagnosis help, including a handy damage comparison table with helpful photos, can be found here.
Collect and submit hull samples at harvest for B analysis. For more information, see here.
Apply a last shot of nitrogen either shortly before or just after harvest to support bud development for next year. Generally, no more than 20% of the total season’s nitrogen should be applied between hull split and early post-harvest. Decrease planned application if July leaf levels were higher than 2.8% N. In blocks with a hull rot history, the target leaf N level is 2.6%. If planning postharvest N application, do it early. October N applications have not improved yield the following year in several years of research.
Manage post-harvest irrigation to minimize water stress. Water stress in late August to early October can interfere with flower bud development for the following spring. Fewer flowers will mean less crop next year. Defoliation reduces tree vigor by reducing sugar production. This is particularly important for orchards with a long window between harvest of Nonpareil and late pollinizers.
Assess hull rot and shaker damage post-harvest. Hull rot symptoms can be found here.