Luke Milliron, UCCE Farm Advisor, Butte, Glenn and Tehama Counties
Franz Niederholzer, UCCE Farm Advisor, Colusa and Sutter/Yuba Counties
Clarissa Reyes, UCCE Farm Advisor, Sutter-Yuba, Butte, Placer

Harvest: Timing is Everything 

The period from shaking until pick up is one of long days and high stakes in almond production. With the objective forecast for a three billion pound crop for the state, up almost 10% from last year, this year could be one where harvest timing decisions are even more critical to a successful season. The decision of when to shake will in-part determine nut removal, navel orangeworm (NOW) pressure, risk of trunk injury, and quality/grower income. In-short, the critical decisions in this final sprint can determine how financially successful this season will be. There are pros and cons of any harvest timing for Nonpareil, while specific shake times for certain other varieties improve nut removal and so may dictate harvest timing. At the end of the day, the decision to shake is a block-by-block grower call.  

When do you shake Nonpareil? 

Stage 2C-3: Should it be a “timely harvest”, one that begins once test shakes show virtually all nuts (96-99%) are removed? That depends on the orchard and the operation. Although you should get very good nut removal as soon as you have one-hundred percent hull split (all hulls are at least at 2C, figure 1 above), it might not make sense for your operation. The major advantage of this ASAP shake timing is a reduction in NOW pressure, with nuts being less vulnerable once they are on the orchard floor. Additional pros include fewer wrinkles on kernels if there is subsequent tree water stress, hulls generally dry faster on the ground, and it spreads out equipment use if there’s a lot of acreage to get to. However, shaking at an earlier hull split stage (greener hulls) means longer drying times on the orchard floor (7-14 days vs. 4-7 with later hull split stages), and greater susceptibility to ant and Carpophilus truncatus damage. Additionally, the best nut removal for Nonpareil and maximum kernel dry weight occurs as the nuts reach approximately stage 3, although most of the crop will be far past this stage when the last, lower nuts get to 2C and the trees are ready for timely shake. More foreign material can result when trees are harvested early, this comes in the form of curled hulls from rapid drying on the orchard floor or hull tights. Harvesting too early can prevent color from developing on the pellicle, which reduces nut quality. A final reason to not shake when hulls are on the green side is the earlier you shake, the higher the risk of barking. 

If you see a lot of green (often Stage 2C or 3) in your windrows, conditioning can accelerate drying. Cleaning up windrows with conditioning can also speed up the actual “pick-up” process and potentially reduce hulling/shelling costs since many hullers now charge on incoming weight. 

Stage 4-6: At these later hull split stages, 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.  For Nonpareil, nuts at stage 5-6 have the highest chance of being cleanly hulled and receiving an inshell price premium. This stage also has the shortest possible drying time on the orchard floor (4-7 days). On the downside, shaking at stage 5-6 means that the nuts “hang” longer and face the risk of higher NOW damage compared to earlier harvest timings. Later hull split stage shaking also lowers the risk of harvester damage (“barking”) as the bark tightens as the season progresses. In some cases, the long-term health of an orchard (no bark damage) could be the driving point in deciding to shake late. 

Other Varieties:
While the ideal shake time is not known for all other varieties, shaking strategies for some varieties are clearer. For example, the industry is still learning when to shake ‘Independence’ for maximum nut removal. Some growers swear by an earlier shake (heavier nuts), lumping it in with the earlier shake strategy they would also pursue for ‘Winters’ or ‘Padre’.  

To avoid water stress on later-maturing pollinizers, irrigation with drip or micro sprinklers should be applied between harvests. If this is not possible, severe water stress may result in stick-tights (nuts stuck in the tree) and/or hull-tights (green hulls shriveling and drying tight around the nut). ‘Winters’, ‘Padre’ and other mid- to late-harvesting varieties can be posterchildren for stick-tights when water stress and a late shake combine. An excessively late harvest can also result in mite infestation, and defoliation on later-maturing varieties. Extreme defoliation robs the tree of carbohydrates and can reduce bloom the following spring and may reduce yield next harvest. 

Conclusion: Harvest timing can be very important. It influences nut quality and grower returns. There are many factors that influence almond harvest timing, 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, harvest logistics, and nut quality. 

Regardless of when you shake, it is necessary for nuts and hulls to be dry when delivered to the huller because stockpiling nuts with high moisture content is detrimental to nut quality. Work with your processor on deciding pickup timing.