Watering Pecans

This time of year or sooner I am often asked how late do I water my pecans. Years ago we recommended stop watering at the end of September to harden the trees for winter. It was also believed (not research proven) that reducing the water on pecans help to prevent stick tight where the nut won’t come loose from the shuck. About 15 years ago now University of Arizona and New Mexico State University completed a cooperative research project and disproved many common myths about late watering pecans. A couple years later Texas A & M duplicated the research with similar results. Before we go to deep into this we need to talk about watering pecans in general. Our recent rain has really reduced the need to fall water pecans, but as it warms up and dries up be watchful not to meet the tree’s needs. Pecan trees extract the moisture they need from soil in the root zone daily during the growing season. The amount a tree withdraws may vary from a gallon or less for a young tree to as much as 150–250 gallons per day in a fully mature tree. This water demand is the tree’s peak (maximum) water use on the hottest day of the summer. Water consumption is decreased before and after this maximum use. “Consumptive use” is generally expressed in a withdrawal rate of a fractional amount of an inch of water per day for an area, enclosed by the drip line for a small tree or the total field for a mature orchard. Consumptive use varies with the tree’s growth and its stage of the nut-bearing cycle, but it generally falls in a range of 1/4" per day in the early season to a maximum of 1/2" per day during the month of August in southern Eddy County area, which occurs at the nut’s water stage. Consumptive use by pecans varies with different geographic areas and climate conditions. As soil moisture is depleted, it becomes more difficult for plant roots to extract needed moisture. When about 50% has been depleted, soil moisture must be replaced. In addition to reducing plant stress, this also gives leeway in watering operations with respect to the time required to cover the orchard. The ideal water management efficiency for a pecan orchard, which calls for optimum water moisture available (no stresses), leading to maximum protection potential is difficult to achieve in practice. Stresses are often not visible and damage can occur. Using an infrared thermometer could help detect water stresses at an early stage. These stresses can then be corrected before any harm can occur. Summer rainfall sometimes helps satisfy the water requirements, but most of the time in the arid southwest, water from rainfall does not amount to much; growers, therefore, should not reduce the quantity of irrigation water needed. Do not forget to allow extra water if it is salty. With this understanding it does not help to stress a tree in the fall. With the nuts mostly mature and hardening off the tree need to produce photosynthetic sugars to convert into carbohydrates which are stored in the root to start growth in the spring. The consumptive use of the tree is reduced in the fall they do not need to water as often, I prefer to put on the same amount of water on at one time but to spread it out between watering by lessening the frequency. As long as there a leaves on the tree some water is needed. The fall is also a good time to apply an application of phosphorous. Phosphorous take time to mineralize into useable form and the winter is good time to do that and because you have cut back on your watering it won’t be as likely to leach past the root zone. As to stick a tights that is still a little of a mystery but in general late watering actually reduced the amount of stick tights, but not statistically. So the research is still looking for that answer. Eddy County Extension Service, New Mexico State University is an equal opportunity/affirmative action employer and educator. All programs are available to everyone regardless of race, color, religion, sex, age, handicap, or national origin. New Mexico State University, U.S. Department of Agriculture, and the Eddy County Government Cooperating.