Preparing for Harvest

It looks as if harvesting will be underway for Merced County within the next week to 10 days, with the date occurring earlier for growers on the West and South Sides of the county. With harvest, there are many preparations that must be taken into consideration.

Water Management:
In order to determine the last pre-harvest irrigation, a target harvest date must be set. Approximately two weeks after the last irrigation are required to “dry down” the trees enough to minimize bark damage from shaking. This time period does vary upon soil textures, with sand and clay requiring less and more time, respectively. This depletion of soil moisture tightens the bark to the trunk and prevents damage from the shaker attachment. Also, as the season progresses, the bark adheres tighter to the trunk. Therefore, with an earlier harvest, the chances of shaker damage are increased.

In soils of low water holding capacity (i.e. sand) it may be necessary to irrigate between the harvesting of the varieties. Proper water management between varieties is just as critical as water management before harvest because during this period the tree is developing the fruit bud for the coming season. Any moderate to severe water stress during this period will reduce the formation of fruit bud.

Timing of Harvest:
Harvest timing should be considered using the following criteria:
– The need to avoid naval orange worm damage to nuts on the tree and ant damage once nuts are on the ground;
– The ability to achieve maximal nut removal;
– The ability to maintain yield and quantity;
– Minimization of tree injury;
– Availability of harvest equipment;
– weather conditions that may cause crop loss or damage (i.e. rain).

A few of these points are highlighted below:

Damage caused by Navel Orange Worm and Ants:
Early harvest prevents the damage caused by Navel Orange Worm (NOW) as it reduces the number of eggs laid on the shaken almonds. The NOW moth prefers to lay its eggs on almonds that are still within the tree canopy, thus almonds that are shaken before the emergence of the third generation larvae will have less damage than almonds shaken after this period. Growers of Nonpareil should begin the harvest before this upsurge in worm pressure begins. Later harvesting varieties may have more exposure to NOW, but an earlier harvest of worm-infected Nonpareil nuts will still reduce worm pressure for these later varieties.

With Ants, it is just the opposite. The longer the nuts are on the ground to dry, the more ant damage can be expected. Many growers therefore place baits (Pyriproxyfen, Abamectin, and/or Methoprene)6-8 weeks prior to harvest to selectively reduce the ant populations that fed on the almonds. If the populations of the almond feeding ants are still high at harvest, it is possible to control ants by making an application of broad spectrum insecticide (Chlorpyrifos) to the soil surface to kill any emerged ants.

Achieving maximal nut removal:
The formation of an abscission layer between the nut and peduncle is needed in order to shake the almonds from the tree. Once the abscission layer has formed, nut removal may be as good as it is going to get. Letting the hulls dry too long on the tree may cause a higher frequency of stick-tights, either causing a loss of crop or requiring a second shake. A good, properly timed shake should remove about 99% of the nuts.

Determining when to begin harvest:

To determine the start time of the harvest, strike a tree limb and see how easily the nuts come off. If conditions appear to be about right, test shake a few trees. Once 99% of the nuts are shaken from the test trees, begin shaking the entire orchard. Determining when to shake the whole orchard should not just rely on nut removal. upon shaking, observe the bark to see if any damage has occurred. Check for signs of bark breakage, water soaking, or wet lines on the shaker pads. If any sign of tree injury occurs, wait a few days and try again. Bark damage is one of the main means of entrance of the scaffold and trunk pathogen Ceratocystis fimbriata.

Mechanical shaking can be tried as soon as the interior orchard trees reach 100% hullsplit. For mature trees, tree nut removal is maximized when shaking at 100% hullsplit. Once the nuts are shaken to the ground, a hullable product should be expected within 2 weeks.

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