Reprinted from Ag Alert
Peach, nectarine, plum: Early season varieties should receive full irrigation through harvest. Post-harvest water can be appreciably curtailed except during bud differentiation, usually mid- to late August, to prevent fruit “doubling.” Late varieties can be stressed during stage two fruit growth, usually about four weeks after fruit set, when pit hardening occurs through the start of rapid fruit growth in stage three and during post-harvest. Clings should not be stressed in late stage one or early stage two and then irrigated heavily in order to limit “split pit.”
Apricot: Apricots can be stressed during the middle part of fruit development, but should receive full irrigation early in the season and during rapid fruit growth just prior to harvest. Excessive post-harvest stress can result in bud drop, reducing the following year’s crop, so the soil profile must not be allowed to dry out after harvest.
Cherry: Cherries should be fully irrigated until just before harvest. Except during the bud differentiation period when irrigation is required to prevent “spur fruit.” Post-harvest deficit irrigation can be used.
Prune: After full irrigation through the rapid initial fruit growth phase – about lat May – reduced irrigation can be tolerated with little if any effect on fruit size, weight or drop. In fact, stress during this period may increase flowering the following season. Severe stress during fruit development, followed by heavy irrigation, can result in cracking. Post-harvest irrigation should be geared to preventing premature defoliation.
Walnut, pecan: For hedgerow plantings, some water should be applied throughout the season except for the final two or three weeks in the fall. The appropriate percentage of normal amounts to apply depends on available water supplies. With about 20 acre-inches available, growers should irrigate at about 50 percent of normal rates. With 10 acre-inches per acre available, growers should apply about 25 percent of normal rates.
Research found conventional density plantings suffered an 80 percent yield reduction in the year following a simulated drought when a total of 16 acre-inches per acre was applied – mid-March to late May – followed by a progressive cutback through harvest.
Spreading out applications over the season for hedgerow plantings appears to be a better strategy. For heat sensitive cultivars, irrigating at near-normal levels in the two-week period before harvest may reduce sunburn. Applying whitewash may also lessen sunburn damage.
Almond: In almonds, full irrigation early in the season is important for good fruitwood growth and therefore necessary for long-term tree productivity. In early to mid-season cultivars, irrigation can be severely curtailed between mid-June and harvest, this is about a two-month period.
Later harvest cultivars can also tolerate a two-month period of sever water deprivation before harvest. This practice will reduce kernel weight by only about 10 percent, but will drastically reduce hull split. Resuming full irrigation two weeks before harvest can improve splitting.
For almonds planted on shallow or drip irrigated soils, post-harvest water management is crucial for the following year’s crop. Recent research showed that post-harvest water deprivation reduced fruit set and, to a lesser extent, also reduced bloom.
Growers should reserve at least three to four acre-inches per acre (of the normal eight inches) for post-harvest irrigation. Irrigation should begin as soon as possible after harvest,
With deep soils that are surface or sprinkler-irrigated close to harvest, a post-harvest irrigation may not be as important. Prematurely defoliating trees indicate inadequate irrigation. Pre-harvest defoliation followed by post-harvest irrigation can lead to refoliation (a new canopy).
Contrary to conventional wisdom, this practice benefits the tree by improving tree water status during a critical period of flower morphogenesis. Flowering in the late fall, however, will reduce yield the following year.
This occurs when orchards refoliate in the fall and when cold weather in October is followed by a warm November. Limiting irrigation during the late fall may deduce premature flowering.
Pistachio: Pistachio trees are fairly stress tolerant from leaf-out through mid-May. Stress during this period may actually enhance shell splitting at harvest, but at the expense of nut size.
Research indicates that a controlled deficit irrigation strategy where stress is imposed after the full shell size is attained, about mid-May, and before rapid kernel growth occurs in early July results in little or no negative impact on production.
Severe stress from late June through mid-August will reduce harvestability and modestly reduce shell splitting. Water deprivation from mid-August through harvest, about mid-September, will decrease shell splitting and slightly reduce harvestability. Severe post-harvest water stress can be tolerated.
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