Note (2014): The 1979 almond crop suffered significant post-bloom nutlet drop in March. The following portion of our 1979 newsletter focuses on the importance of late-season irrigation to maintain leaf numbers that provide nutrition for developing nutlet the following spring. Prior to 1979 most UC Extension personnel cautioned against a post-harvest irrigation, a major concern being the possibility that wet soils would increase the chance of phytophthora and/or crown rot. UC studies subsequent to 1979 established that a post-harvest irrigation is indeed very important and can increase yields by up to 500#/acre or more. Today, almost all almond growers apply a post-harvest irrigation, a major reason for significantly higher state-wide almond yields.
Small developing almonds (or any fruit) undergo a tremendous growth surge after petal fall and it is at this time that food demands on the tree are the greatest. These small developing nuts get their food from 2 sources: 1. Food stored in the tree from the previous year. 2. Food manufactured by the leaves during the current year.
There are significant differences in almond crops among orchards this year . Our observations are that orchards that kept a crop of healthy , functioning leaves until normal leaf drop (in late October) have a better crop this year than orchards that suffered premature defoliation (due to mites or too long a period without water at harvest). Keeping healthy leaves on trees as long as possible will maximize storage reserves.
The breakdown in irrigation in otherwise well managed orchards comes at harvest time. The current crop is made and the fruit buds are set for next years crop; the general thinking is that this is the one time of year that is least critical if a tree stresses for moisture. This, however, is the time when the major portion of nutrients are being stored for next year. Maintaining productive leaves for another few weeks by maintaining soil moisture reserves can increase the stored food reserves.
Once a tree has been severely stressed for water at or before harvest, a post harvest irrigation can do more harm than good by triggering a new flush of growth that will diminish the supply of stored nutrients. The key is not to allow the tree to stress.
Some growers hold that it is impossible to maintain adequate irrigation on all varieties in combination with a timely harvest and this may well be true for some orchards under some irrigation systems. The fact remains that the best crops this year are those where the trees were not stressed for water at harvest last year.
Joe Traynor (April 1979)