An important consideration in planning is addressing the period of bud differentiation for next year’s crop, which starts about mid-August and continues through the month of September. Moderate stress during this period will have little effect on subsequent years’ nut numbers, but severe stress during bud differentiation has dramatically reduced fruit set the following season, according to research.

Once the season commences, starting at bloom, real-time estimates of ETc (=Kc*ETo) are available using the California Irrigation Management System (CIMIS) online at Starting at bloom, keep a running total, and also account for any meaningful rain and irrigation/fertigation.

When water supplies are severely restricted, the impact on almond trees and crops is unavoidable. Yields are reduced in the drought year as well as the subsequent year, with reduction proportional to the degree of stress. Fortunately, production recovers by the second to third season after drought with sufficient water supplies.

UC researchers have urged growers not to take aggressive actions in reducing tree size or crop load in response to water shortages this year. Severe pruning will increase new growth, which would increase the leaf surface and ETc of the tree. Crop thinning has a similar effect and is also not recommended. By reducing crop load, the source/sink ratio of the tree is disturbed, causing the tree to put nutrients into vegetative growth instead of the nuts. Furthermore, in-season nitrogen applications should also be reduced in order to reduce vigorous shoot growth.

Irrigation System Accuracy

Other important actions under these conditions are to control weeds that compete for water, and to be sure your irrigation system is performing optimally. According to Jim Anschutz with Ag/H2O, a member of the Water, Energy and Technology Center at Fresno State University, it takes 1.8 acre-feet of water to compensate for a distribution uniformity (DU) of 75 percent.

Speaking at the annual conference of the California Irrigation Institute in Sacramento in January, Anschutz added that a 10–15-year-old system may have a DU as low as 45 percent to 65 percent, and at a DU of 75 percent in almonds, the potential loss of revenue at $3 per pound would be $570 per acre. UC Davis has developed guidelines for DU testing, which are published at

At a Jan. 28 almond drought management meeting, David Doll and Ken Shackel also noted the following very important issues:

• Under deficit irrigation, expect to see differences in tree water stress according to soils. Use the pressure chamber to identify areas of stress and adjust your irrigation approach before these areas become a severe problem.

• There is no evidence that heavy pruning, kaolin/whitewash sprays or reducing bud/crop load do any economic good to mitigate drought conditions.

• Fertility programs need to be throttled back, but not lacking. For instance, in-season adjustments for nitrogen should be based on early-season leaf sampling (see coupled with crop estimation.


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