Wet 0 to -4

Field Capacity

Good -4 to -6

Low to mild stress. Promotes shoot growth. Suggested level from leaf-out until mid-June, when nut sizing is completed. Should maximize rate of shoot growth in young nonbearing trees. (-4 to -6)

Slight/Moderate Stress -6 to -8

Mild to moderate stress. Shoot growth visible but the rate of growth may be reduced. These levels do not appear to affect kernal development or bud fruitfulness for next season. May use to control tree vigor, if desired. (-6 to -8)

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Dry -8+

Moderate to high stress. Shoot growth in non bearing trees may stop, nut sizing may be reudced in bearing trees, and bud fruitfulness for next season may be reduced. (-8 to -10)

High stress. Temporary wilting of leaves and hull shrivel has been observed. New shoot growth may be sparse or absent, and some deoliation may be evident. Edible yield likely to be reduced and kernal color darkened. (-10 to -12)

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High stress. Wilting observed. Some defoliation. Impacts yield potential. (-12+)

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https://anrcatalog.ucanr.edu/pdf/8503.pdf