Clarissa Reyes, UCCE North Sacramento Valley Orchard Systems Staff Research Associate,
Luke Milliron, UCCE Farm Advisor, Butte, Glenn, and Tehama Counties,
Franz Niederholzer, UCCE Farm Advisor, Colusa and Sutter/Yuba Counties
Almonds can be harvested as soon as 100% of the nuts on the tree reach hull split. 100% hull split occurs when the lowest nuts in the lower interior canopy reach stage 2C (Figure 1): there is a deep V at the suture and the nut splits open when hand pressure is applied to opposite ends of the hull. Historically, the recommendation from UC almond experts for the ideal time to shake was as soon as 100% hull split occurred throughout the orchard, keeping in mind pest and disease management, nut removal/drying time, and nut quality. However, these considerations vary widely among varieties and locations, so we would like to address potential challenges that growers should consider when timing harvest.
Pest and disease management:
Early harvest is an effective way to manage navel orange worm (NOW) by reducing the amount of time a nut is open and vulnerable to infestation. Additional NOW infestation risk is reduced once nuts are shaken to the orchard floor.
Early harvest has also proven to reduce the incidence and severity of hull rot in trees by reducing the amount of time a nut is open and vulnerable to infestation by fungi, and by reducing the amount of time an infected hull may transfer the toxin through the shoot.
A rapid removal of nuts from the ground can minimize ant feeding damage. However, shaking just at 100% hull split stage (greener hulls) can mean longer drying times on the orchard floor and greater vulnerability to ant damage.
Nut removal/drying time:
If shaken when hulls are still very green (stage 3 or earlier), nuts will require a longer drying time on the orchard floor. Sweeping nuts into windrows soon after shaking followed by conditioning windrows accelerates drying on the ground. Conditioning also provides the benefit of getting cleaner product from the field, speeding up the actual “pick-up” process, and reducing hulling/shelling costs (since hullers charge on incoming weight). Kernels and hulls must be dry when delivered to the huller because dry product processes rapidly and stockpiling nuts with high moisture content is detrimental to nut quality.
For Nonpareil at stages 4-5, the abscission zone (the separation zone between the fruit and the peduncle) has formed, nuts are only attached to the tree by a few fibers, and removal is normally excellent. Nonpareil normally shakes very well with a harvest timing of 100% hull split. Some varieties like ‘Padre’ and ‘Independence’ can have better removal when hulls are greener and nuts are heavier.
An early harvest of Nonpareil typically requires an earlier water cutoff date compared to that for a later harvest. Hulls dry more quickly on the ground than when nuts are attached to the tree, thus advancing pickup. However, a longer drying time on the orchard floor, 7-14 days with early harvest vs. 4-7 days with later hull split stages, can prolong the time between irrigation and harvest for later-maturing varieties. To avoid water stress in the orchard, irrigation with drip or micro-sprinklers can be applied between variety harvests. If this is not possible, severe water stress may result in sticktights (nuts stuck in the tree) and/or hulltights (green hulls shriveling and drying tight around the nut) on later-maturing varieties and risk of mite infestation, and/or defoliation on all varieties. Extreme defoliation robs the tree of carbohydrates and can reduce bloom the following spring.
In the event of severe wildfires, smoke traps moisture in the air, extending overall drying time. This impacts hull moisture, harvest readiness, and drying time on the orchard floor. If smoke causes delayed drying and increased drought stress on trees, sticktights and/or hulltights can occur. If so, this may reduce nut removal and/or require shelling at the huller to remove the hulls, causing the grower to miss out on inshell premiums on a portion of the delivery.
Almond bark “tightens” and is less vulnerable to shaker damage as the harvest season progresses. Limiting trunk damage (“barking”) risk at early harvest of Nonpareil requires attention to hull split status throughout the orchard. Localized areas of delayed hull split relative to the rest of the orchard may exist due to higher soil moisture (heavy clay streak, uneven irrigation distribution uniformity (DU), low spots in the orchard, etc.). These trees may not shake “clean” at the same time as the rest of the orchard. Trees with delayed nut maturity may be shaken harder by a less experienced, poorly trained operator trying to “get all the nuts off”, resulting in trunk damage that limits the tree life and orchard productivity if enough trees are damaged.
Stage 5 and 6 nuts have the highest chance of being cleanly hulled and receiving an inshell price premium. Harvesting too early can prevent color from developing on the pellicle (kernel skin), which reduces nut quality. Shaking early can also result in nuts that form curled hulls from rapid drying on the orchard floor. These curled hulls are similarly sized to kernels, difficult to separate, and may contribute to increased foreign material.
Many factors influence almond harvest time, including equipment scheduling, weather, irrigation timing, NOW pressure, and the potential of an inshell premium with shaking at a later hull split stage. With all these things in consideration, it is important for growers to prioritize their goals for the crop. Growers must account for site-specific challenges whereby subtle changes in the date of shaking help to mitigate costly problems with pests and diseases, nut removal, and nut quality.