Late-season irrigation is critical to ensure adequate fruiting
buds in the following season.
In this series on coping with drought, the Almond Board has been providing information and tools largely resulting from Almond Board–funded research to help growers cope with tight water supplies.
An important principle to follow if water supplies are severely restricted is to spread out available water over the season in proportion to almond crop evapotranspiration (ETc). The April and May issues of California Almonds Outlook provided instructions for calculating and using ETc as a guide.
A key objective is to supply water for the entire season, saving some for late season. Water is needed during the period of fruiting-bud differentiation, which in normal years starts in July and
continues to mid-September, or even into October for later varieties and cooler years. Moderate stress during this period will have little effect on the subsequent year’s yield; however, severe stress can dramatically reduce bloom, fruit set and yield the subsequent season.
Studies done by David Goldhamer, emeritus UC irrigation specialist, and Mario Viveros, emeritus farm advisor, Kern County, on the Nonpareil variety demonstrated that lack of any irrigation after Aug. 28 on a shallow, 3-foot sandy loam soil in Kern County drastically reduced nut set by 74% and yields by 62% the following season.
Subsequent studies on timing of almond fruiting bud and flower development by Bridget Lamp (formerly UC Davis, Plant Sciences), Dr. Vito Polito (emeritus UC Davis, Plant Sciences) and UC farm advisors Joe Connell, Roger Duncan and Mario Viveros provide insights into this yield reduction. Stress that occurred during the period of bud differentiation and flower development
adversely affected flower quality to the extent that the next season’s crop was reduced. These studies tracked flower bud development of the Nonpareil, Carmel and Butte varieties.
Bud development is a gradual process, with beginning and endpoints that range over windows of time, depending on individual buds. For Nonpareil and Carmel, the initiation of flowers spanned the period of July through mid-August.
Flower bud differentiation is completed with pistil development; for the Nonpareil and Carmel varieties this occurred
from August to mid-September. Bud development for the Butte variety was somewhat later and in a colder year (1998), and was not completed until the first part of October.