Weekly Tree Nut Report: Almond Cankers, Boron and Walnut Frost Prep

October 14, 2026

The Weekly Tree Nut Report from West Coast Nut arrives every Wednesday with field intelligence for California almond, pistachio and walnut growers and their crop consultants. Subscribe free to get it by email.

Research through October 13, 2026 (Pacific). This week’s field priorities: distinguish almond canker problems before prescribing, review red leaf blotch prevention timing, verify pistachio sanitation, and use tissue results and soil moisture to guide fall decisions. Each brief pairs source findings with a suggested consultant work product.

This week in numbers

• 35–40 days between almond red leaf blotch infection and visible symptoms.⁶
• 80 ppm: the harvest hull boron level below which UCCE rates almonds deficient.⁹
• +19%: almond shipments for August–September (422.6 million lbs) vs. the same months of 2025.¹

For PCAs: Disease and Pest Management

1. Almond cankers: diagnosis determines the plan

Recent update · UC IPM almond guideline, September 2026

UC IPM’s new aerial Phytophthora page distinguishes an annually recurring canker problem from perennial Phytophthora and root and crown disease. Aerial infections tend to involve pruning wounds or young shoots during cool, wet periods; in the Central Valley, canker expansion stops with higher summer temperatures. UC warns that these cankers can resemble Ceratocystis and band canker.^4,5

Inspect: Record where lesions originate (pruning cut, twig junction, crotch or crown) and whether the history suggests seasonal or persistent expansion. These are diagnostic clues, not a laboratory confirmation.⁵

Consultant decision: Build a suspect-tree map with photographs and request diagnostic confirmation where needed before selecting a disease-specific program. Review pruning dates against rain forecasts; UC recommends avoiding rainy-period pruning.

Deliverable: A block-specific diagnosis and pruning plan, with unresolved cases clearly marked.⁵

Sources: UC IPM: aerial Phytophthora in almond · UC IPM: what’s new

2. Red leaf blotch: audit prevention timing

Guideline update · UC IPM peer review announced September 29, 2026

UC IPM describes one primary infection cycle, with infections beginning after petal fall and potentially continuing until May. Symptoms can lag infection by about 35 to 40 days. Its guidance states that fungicides applied during bloom or after symptoms appear are ineffective against this disease.^4,6

Interpret: A symptom-date spray record may miss the earlier infection window. Suggested review: align confirmed disease observations with petal fall, rainfall and application dates before concluding that a product failed.⁶

Consultant decision: Audit the 2026 program and draft a prevention schedule for 2027 using current efficacy guidance, FRAC rotation and verified California labels. Infected fallen leaves supply primary inoculum; UC cautions that litter-management practices require a wide-area approach.

Deliverable: A timing and resistance-management review, not an automatic product substitution.⁶

Source: UC IPM: red leaf blotch in almond

3. Pistachios: verify what sanitation actually removes

Seasonal reminder · UC IPM pistachio guideline, June 2019

UC IPM links navel orangeworm carryover to unharvested nuts and emphasizes both removal and destruction. Its sanitation guidance includes nuts in tree crotches, on berms and on the soil surface, not just those visible along drive rows.⁷

Suggested monitoring: Establish repeatable inspection locations and record residual nuts separately in trees, crotches, berms and row middles. Revisit the same locations after cleanup. This is a proposed documentation method, not a validated treatment threshold.⁷

Consultant decision: Specify which remaining areas need another pass and how removed nuts will be destroyed. Review harvest-damage records alongside the inspection to prioritize follow-up; do not assume every reject is navel orangeworm.

Deliverable: A before-and-after sanitation record with remaining work assigned.⁷

Source: UC IPM: navel orangeworm in pistachio

For CCAs: Nutrition and Orchard Management

4. Almond boron: separate deficiency from a foliar opportunity

Seasonal research · UCCE Sacramento Valley, October 4, 2025

UCCE identifies harvest hull boron below 80 ppm as deficient, notes potential yield response below 150 ppm, and advises against boron fertilization at hull levels of 300 ppm or greater. These are hull-analysis values, not interchangeable leaf-test thresholds.⁹

Interpret: Record the tissue, sampling date and block before classifying a result. Deficiency correction and supplying boron to next spring’s buds are different objectives. UCCE notes that postharvest soil application does not increase flower boron the next spring, and it does not recommend fall foliar boron where postharvest defoliation is extensive, suggesting a pink-bud spray instead.⁹

Consultant decision: Match hull results with canopy condition and prior boron inputs. Where the evidence supports treatment, develop the block-specific rate and application method; missing or mismatched tissue data should trigger verification.

Deliverable: A documented correction, foliar-treatment or no-addition decision, not a calendar-based spray.⁹

Source: UCCE: fall zinc and boron review

5. Walnuts: build a block-specific freeze response

Seasonal reminder · UCCE Sacramento Valley guidance from 2024

UCCE distinguishes young-tree hardening from mature-tree postharvest recovery. Young trees should resume irrigation after terminal bud set; moisture management for mature blocks should address postharvest stress. The guidance favors a moist soil profile and surface without saturation or ponding, and says remote freeze-alarm monitoring makes good sense. Growers hit by earlier autumn freezes reported that having frost alarms ready and on by October 15 helped.⁸

Inspect: Separate young and mature blocks; check terminal buds, soil moisture, cold pockets, groundcover and irrigation function. Confirm whether the system can support the proposed response rather than assuming routine irrigation provides frost protection.⁸

Consultant decision: Agree on the forecast and field conditions that trigger a response, who monitors alarms, and who operates irrigation.

Deliverable: A written block-level action plan. This is preparation guidance, not a current freeze warning or a promise of protection.⁸

Source: UCCE: autumn freeze damage strikes again

Market snapshot: shipments in context

New almond and walnut reports · older pistachio baseline

Almond exports were up 29.30% for August–September, while domestic shipments were down 7.91%.¹

Our take: Stronger shipping volumes are useful context for a handler conversation; they do not establish your orchard’s price or net return. Keep crop periods and units separate, especially walnut inshell and kernel tons.

Next step: Ask your handler how your varieties, size profile, quality and sales position compare with the reported demand.

From West Coast Nut magazine

Carpophilus Beetle Continues to Damage Tree Nut Crops
By Cecilia Parsons · October 13, 2026

Since its first California detection in 2023, carpophilus beetle has spread to tree nut regions throughout the Central Valley and can infest the same nuts as navel orangeworm. UC IPM adviser Jhalendra Rijal shared the latest research at the Crop Consultant Conference.

What are you seeing?

Email info@jcsmarketinginc.com with your crop, county and the field question you most want covered next.

Editorial note: Source findings are distinguished from our suggested next steps. Management decisions require orchard-specific judgment; current product labels and applicable local requirements govern pesticide use. This report does not award CE credit.

Sources

1. Almond Board of California, “Almond Industry Position Report, September 2026,” October 13, 2026, p. 1.
2. California Walnut Board, “Monthly Shipment Report, September 2026,” October 8, 2026, pp. 1–2.
3. Administrative Committee for Pistachios, “Pistachio Industry Inventory Shipment Report (Pounds), August 2026,” reporting period ended August 31, 2026, p. 1.
4. UC Statewide IPM Program, “What’s New,” September 29, 2026 almond update.
5. J. E. Adaskaveg and colleagues, UC Statewide IPM Program, “Phytophthora Pruning Wound and Branch Canker (Aerial Phytophthora),” Almond Pest Management Guidelines, text updated September 2026.
6. UC Statewide IPM Program, “Red Leaf Blotch,” Almond Pest Management Guidelines, peer-reviewed update announced September 29, 2026.
7. R. H. Beede and colleagues, UC Statewide IPM Program, “Navel Orangeworm,” Pistachio Pest Management Guidelines, text updated June 2019; Cultural Control section.
8. Clarissa Reyes and Luke Milliron, UCCE Sacramento Valley Orchards, “Autumn freeze damage strikes again (2024),” September 16, 2024, modified October 22, 2024.
9. Franz Niederholzer, UCCE Sacramento Valley Orchards, “Fall Zinc and Boron Review 2025,” October 4, 2025.