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Water Split in Pecan

From Dr. Lenny Wells

This is just a reminder that given the recent rain and the stage the pecans are in, if you have not seen it already, you we will likely be seeing water stage fruit split on many varieties over the next couple weeks.

Water stage fruit-split of pecan is often a major problem exhibited by thin-shelled pecan varieties (e.g., Schley, Caddo, Oconee, Sumner, Wichita, Frotscher, and Farley) and, to a lesser degree, by certain relatively thick-shelled cultivars (e.g., ‘Cape Fear’ and ‘Elliott’).  The problem occurs when water pressure builds up rapidly inside the nut, causing the shell, seed coat, and sometimes the shuck to split about the time of the initiation of kernel filling and shell hardening, resulting in abortion and drop of damaged fruit about 7 days after splitting.

Water split is highly erratic, with incidence and severity varying depending on cultivar, location, and year. Crop loss can be severe in certain years and nearly absent in others.  It occurs during the “late water stage”; a time when turgor pressure inside the nut is high and the shell is beginning to harden.  This typically occurs during mid-August for susceptible cultivars growing in the southeastern U.S.

Water split is associated with rainfall occurring at the initiation of shell hardening. There are usually 2 episodes to water split. The major episode is usually triggered by rainfall (or potentially irrigation) and a relatively minor event triggered by “high humidity/low light”.  Irrigation schedule, shading, and crop load also factor in.

Often, the split is inside the nut and you will simply see green nuts on the ground, which will stain a few days later. Other times when the incident is particularly violent you will see an actual longitudinal split in the shuck itself.

By the time you see water split, there’s little that can be done. Crop loss to water split is minimized, but not totally prevented, by managing soil moisture to minimize the severity and duration of water stress during the last two weeks of fruit sizing, and by crop-load thinning.  Certain varieties will always have a potential for it under the right conditions. It seems to be worse when there’s been a dry spell and you suddenly get a heavy rainfall or crank up the irrigation all of a sudden.

Water split also appears worse when the trees are bearing a heavy crop load. Therefore it will likely be more noticeable in most orchards this year. Trees with a heavy crop load appear to kick off more nuts with water split but often, the precentage of nuts you lose from a heavily loaded tree is no higher than what you see in “off” trees, you just have more nuts to lose.

Don’t panic when you see water split. It is a normal physiological response of the tree to environmental conditions and it will end with much less reduction in yield than it at first appears.