Irrigating from Hull-split to Harvest

Irrigating during hull-split and prior to harvest can be tricky. Irrigating too much can increase diseases, the risk of shaker damage, and delay shaking. Too little can increase stick-tights, increase mites, and decrease kernel weights.

During this time, consider maintaining the same frequency of irrigation, but making the adjustments in the duration of the irrigation sets. Reductions to irrigation (i.e. 50% at the onset of hullsplit) to apply a stress can be made by reducing the duration. Trees should be monitored by either a pressure chamber or observations (i.e. wilting) to identify stress levels. If the trees are over/under-stressed at the end of the cycle, adjust the duration.

A basic strategy from hull-split through post harvest could be: 
Hull split initiation, week 1: 50% reduction to reduce the incidence of hull rot and even up hull-split (-15 bars with the pressure chamber)
Hull split, week 2: 30-50% reduction to reduce hull rot (-15 bars on the pressure chamber)
Hull split, week 3: 0-30% reduction to reduce hull rot, based upon tree stress the past two weeks (2 bars more negative than baseline). A mild deficit at this point should cause minimal loss in kernel weights, but will save some water. It will not increase the process of hull-split – this is a physiological process. A severe deficit may impact kernel weights.
Post Hull split, week 1: 100% ET – irrigation reductions at this time can decrease kernel weights until the final abscission layer between the peduncle and nut is formed (2 bars more negative than baseline).
Post Hull Split, week 2: Depending upon timing of harvest – 100%ET if more than two weeks from harvest.
Pre-Harvest week: 20%-50% reduction to help begin a slight dry down of the orchard.
Harvest week: 30-50% ET – some water should be applied, but with enough time to allow orchard floor drying for shaker movement.
Post Harvest: 100% ET – stress should be minimized at this stage as the tree prepares for next year.

The recommendations above are made for micro, drip, or solid-set irrigation systems, but the recommendations would be very difficult to achieve using flood irrigation. With flood irrigation, growers will want to adjust their irrigations so that some trees show signs of water stress between irrigations during hull split, and harvest will be delayed until the wettest part of the field is dry. Increasing distribution uniformity by taking into account soil differences with different checks may help with a uniform harvest.

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13 thoughts on “Irrigating from Hull-split to Harvest

  1. If, you don’t have a pressure bomb, how many gallons per tree/day is a safe reduction. Suppose you use about 80 gallons a day via micros can you reduce it to 45 gallons a day without worrying that your trees are being harmed.

  2. A rough estimate is the percentage of reduction noted with each identified period. For example, for the 2nd week of hull-split, a 30% reduction would want to be applied. In order to get gallons per tree, subtract 24 gallons from 80, giving 56 gallons.

  3. Yes, potentially. Since young trees have developing rootzones, they have less access to deep soil moisture. This makes them more susceptible to deficit irrigation. Irrigation reductions should be made in the hull split and harvest period to reduce hull rot and shaker damage. The other cuts outlined above may create excessive water stress, and should be applied using orchard observations as a guide (wilting, off color, etc.).

    This may seem like a vague answer, and it is. For the most part, we dont really know optimal irrigation practices for developing trees. Most of this research was conducted in the late 80s in which we weren’t expecting the yields we currently receive in the 3rd/4th leaf. We do know that plant based measurements (i.e. the pressure chamber) are able to determine tree stress, regardless of tree age, and thus are recommended to help determine irrigation needs for young orchards.

  4. Will extremely high levels of boron cause stick tight and also gummy nuts and early abortion of almonds especially in Monterey?

  5. Boron toxicity can occur in almonds which has symptoms of gummy nuts, but not pre-mature nut drop. If suspected, boron levels should be determined using a hull analysis – if over 300ppm, boron is in toxic levels.

    Another possibility is anthracnose. Anthracnose will cause nut drop, gummy nuts, and stick tights. The variety Monterey is susceptible to anthracnose. This year, I have seen more anthracnose than in the past few years. I suspect it is due to the late, warm rains experienced over the past three years. To diagnose, look for nuts with a lot of orange gum. Upon close inspection, an orangish-pinkish lesion should be present. If placed in a humidity chamber (plastic bag with wet paper towel), the fruiting bodies will become apparent and an orangish-pinkish slime will become visible.

  6. Dear Almond doctor,

    I dont think it is anthracnose they are only third leaf almond trees and we ran a a good strong fungicide program is there anything else that might cause this?

  7. It may not be anthracnose. Being third leaf trees, I doubt that it is a nutrient deficiency. If it is a toxicity, then the amount in the irrigation water is extremely high, or a mis-application was made.

    Is it possible to send some pictures by email? Try and get a few close ups and a few overview shots. If possible, try and use the macro feature on your camera (usually it is the button with a single flower) to help with focusing on the close-up shots.

  8. Pingback: Notes from the week of July 12th, 2013 - The Almond Doctor

  9. What’s the best way to determine when hull split begins for week 1? When you are able to see the line beginning to separate on some, on half, or on most of the hulls? How do you recommend determining week 1 of hull split in a orchard with pollinators that are 1 and 2 weeks behind nonpareil? Should I just base it off of nonpareil only?


    1. It depends on what you are trying to accomplish and if you have the ability to differentially irrigate your varieties. If it is hullrot reduction, we predominantly see the issue on Nonpareil, and would want a mild stress to be imposed as the nuts begin to split. So reductions should have already began as the nuts in the top of the tree begin to split (pop open with a hard squeeze). This would mean that suture of the nuts in the middle and bottom of the tree are just beginning to widen. Basically, this reduction draws down the deep moisture and helps reduce the vigor of tree as it enters hullsplit.

      We dont see much hull rot in later varieties. This could be due to varietal susceptibility differences, but my guess is that it is also due to these trees being stressed earlier int he season due to practices implemented during the nonpareil dry-down.

      Does that help? If not, let me know…

      1. Using a pressure chamber, how many bars of stress would be safe to minimize barking the trunks? If I dry down too much to reduce bark damage, the trees will be quite stressed in the middle of harvest. Always a balance.

        1. Matt,
          We have not been able to determine a SWP value that would prevent barking. In Dr. Shackel’s research, he demonstrated that trees irrigated fully were not any more susceptible to bark damage than trees that were severely stressed. What he thinks is occurring is that over irrigation tends to lead to to over-vigor, which delays ripening. Nuts that are not mature are harder to harvest, and thus require harder shaking for removal. This harder shaking increases the risk of barking. Here is a link to Dr. Shackel’s work on cambial strength and water status.

          Now the question is “Why are you suggesting a reduction of water as you approach harvest?” Mainly that is a bit of “coffee shop” talk, but farmers have observed and I feel that a bit of a dry down is needed to reduce the amount of water that is moving into the hulls and expedite the drying of the crop. (Too much water moving into the hull keeps them green longer, delaying harvest). This bit of water management really needs some refining, but we are slowly making a few improvements.


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