I have been getting a few reports of hull-split in almonds from varying points across the state. We were expecting an earlier than normal hull-split, but many would agree that this is earlier than expected. Much of the splitting trees are in the more stressed areas of the fields, or in orchards with reduced water allocations. Although I haven’t observed this until this season, early hullsplit induced by spring-time water stress has been described in the literature.
In many cases, when we discuss water stress in almonds, we tend to focus on the post harvest period and the impact on next year’s crop. There are, however, impacts on in-season yields which are dependent on stress timing. Severe tree stress rarely occurs during the initial period of stage one of fruit growth due to stored soil moisture, but if it does, smaller fruit (shell and hull) will be observed due to reduced cell division and expansion. Stress during stage two (Late April/early May through Late May/early June) leads to a reduction in carbohydrates being allocated for kernel fill, leading to smaller sized kernels. Stress imposed during stage three will reduce kernel dry weights, leading to textured or shriveled almond kernels. This loss of kernel weight during stage three is not just due to a reduction of carbohydrates, but also a reduced assimilation of carbohydrates due to an accelerated hull split.
Although cultivar dependent, these two in-season factors – lower cell division or expansion and the disruption of carbohydrate transport into the kernel from an early hull split – contribute to reduced kernel size and yields.
Information sourced from FAO Irrigation and Drainage Paper 66: “Crop Yield Response to Water: Almond” Pgs 358-373.