Avoid Pecan Water Stress

Avoid Pecan Water Stress  
By Larry A. Stein, Extension Horticulturist

The dog days of summer have finally set in! We can all feel the effect of heat stress by walking from an air conditioned office to our cars in the afternoon, so imagine how much water those massive pecan trees need each day to survive such heat.

A pecan tree needs about 100 to 200 gallons of water per day from April through October, which translates into about 2 inches of water every week. Most of the water is lost to transpiration through the stomates, or leaf pores. This transpiration allows the leaves to stay cool and not burn up from the summer heat and enables the tree to make food to feed itself and developing nuts.

There are two critical stages of development in pecan production which require adequate water. The first is early in the season, when the nuts grow to full size (around the end of July); good moisture at this time will mean large pecan size. Since the pecan’s kernels are developed late in the season, late summer and early fall watering is a necessity for well filled kernels. Water will be needed right up until shuck split to not only fill the nuts but also to promote shuck opening. Current research has shown that water stress tends to inhibit shuck opening.

Water should be applied at the drip line of the pecan tree, not at the trunk. It should be a slow, soaking watering since most of the feeder roots are in the top 12 to 24 inches of the soil. Try to wet at least as much soil as is covered by the shadow of the leaf canopy at high noon.

The most recent research indicates that water stress affects nut size, quality, number of viviparous nuts (nuts which germinate while still in the shuck), number of sticktights (nuts which fail to develop and open), as well as the following year’s crop. One of the most significant findings of recent irrigation studies on pecans indicates that the trees’ high water requirement does not end at the end of August or September, but continues up until a week before shuck split. Hence, growers are urged to water late in the season with at least 2 inches of water per week per acre of trees. To a home owner, this represents about 1,000 to l,500 gallons of water per tree, depending on tree size, up until the time of shuck split.

Pecan trees must be watered at least every two weeks; a three week drought is the maximum trees can endure without being damaged. Any stress received by pecan trees during this late stage of development can result in major fruit drop. Some trees can lose up to one-half of their crop if not properly managed during late summer and early autumn.

(For more information on how to water your Pecan Tree, see last week's post on Tree Irrigation)