Photo: California Walnut Board.
- Regulated Deficit Irrigation (RDI) promotes earlier, more even hull split and reduces hull rot. Beginning at hullsplit initiation, shorten normal irrigation time by 50% for the first two weeks. Then catch up the last two weeks before harvest by providing full irrigation (matching ETc). Moderate water stress can be achieved and monitored by keeping mid-day stem water potential between -14 to -18 bars using a pressure chamber. See herefor more information.
- Take leaf samples in mid-July to measure nutrient status. Adjust your nutrient management plan for the rest of the season based on July leaf sample results. See this article for more on collecting samples and interpreting results.
- Codling moth second generation (third flight) occurs in late July to early August (on average, 1100 Degree Days after the second biofix). Check traps to look for the second generation (third flight). 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). Treatment decision is 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. See the UC IPM guidelines for more details.
- Monitor weekly for WHF. If spray residue from the previous spray has run out, harvest is more than 3 weeks away, and eggs are present in trapped females, an additional treatment is recommended. See here for more information.
- Take July leaf samples to assess nitrogen, as well as potentially potassium and zinc deficiencies, and boron toxicity, depending on your circumstances. Sample a total of at least 50 terminal leaflets from at least 10 trees on the same rootstock scattered throughout the orchard.
- Watch for spider mites by monitoring weekly through mid-August. Once a week, randomly select 10 trees per orchard, and from each tree take 5 leaflets from low branches and 5 leaflets from high branches. If more than half the leaflets with spider mites do not also have predaceous mites, this is cause for concern. Monitor again in 3-4 days to determine if populations are increasing and treatment is warranted. For more, see the UC IPM Guidelines.