WHY ARE MY PECANS SMALL?

WHY ARE MY PECANS SMALL? The first thing we have to remember is that nuts are seeds, the tree produces them for propagation, not to give us a notorious food source. So the nut is basically a storage organ that stores mineral, oils, carbohydrates, and other stuff that sustain the pecan embryo until roots and leaves start producing. Nut production by a pecan tree starts with the onset of flowering. Pollen shed from catkins (male flowers) is generally abundant every year. But some year the wind is so hard we may be pollinating trees in Texas. Pecans are wind pollinated and sever wind my move the pollen out of the orchard. Female flowers may be present in adequate amounts or they may be scarce if the crop was good the previous year and alternate bearing is taking place in the orchard. Also the relative humidly can be so low the pollen may not stick. Some flowers may be prematurely shed early in the season. This will include (a) rudimentary flowers located near the shoot tip; (b) normal flowers that were not pollinated, and (c) pollinated flowers in which nutlets did not develop because food reserves were depleted during early growth or because of unfavorable moisture conditions. This shedding, which may occur around May, is worse with some varieties than others and often is not noticed by the pecan grower. Pecan nut growth occurs in two phases. The first phase is nut growth; this determines the size of the nuts. The second phase is nut fill. We are going to discuss the former phase in this article. It takes about 90 days after pollination for the fruit to grow to its full size, slowly at first and then more rapidly. Toward the end of August, the fruit has reached maximum size, so factors influencing fruit size will operate only during the first half of the growing season. The endosperm is not really formed until the beginning of August or toward the end of phase I, which is why it is called water stage. A remarkable feature of Phase I is the slow growth of the actual embryo, which later becomes the edible kernel of the nut. Although the ultimate size of pecans is genetically predetermined, there are some factors that can influence nut size such as soil moisture availability, nutrition status and environmental conditions. The actual size of the nuts produced by a pecan tree is determined by a number of factors, one or all of which may operate during the course of the season. Vigor of tree. In general, it seems young trees are more vigorous and bear bigger nuts than do older trees. In town we see huge tree that are in poor vigor and producer small or few nuts. Where on the tree the nut comes from will determine its size. Nuts in the top of a tree are usually larger than those closer to the ground. Fertility of the soil and available moisture supply. Nuts borne on trees growing on fertile soils adequately supplied with moisture are usually larger than those borne on trees on infertile soil or poorly supplied with soil moisture, of the same type. Small nut size is often the result of small leaf size. Small leaf size is the result of deficiency in micro nutrients like Zinc, Magnesium, Manganese, Iron and the macro nutrient Nitrogen. Except for nitrogen these are difficult to supply by soil applied fertilizer economically and commercial orchards foliar apply. Sample soils in the fall and winter for the macro nutrients and leaf sample in mid-July for micro nutrients and take corrective action as necessary. The number of nuts on the tree or cluster. Commonly, the larger the crop, the smaller the nut. The leaf supplies the nutrients to fill the nut it just can’t produce enough to grow them all large and fill them. So the tree makes smaller nuts. Close to the date when the first phase of nut development is complete, the third nut drop, called August drop, takes place. It usually occurs during the month of August and sometimes stretches into early September. It causes greater concern to pecan growers because of the large size of the nuts at this time, although the percentage shed is generally low, 8–10%. Embryo abortion is considered to be the reason for this late drop. By the time August drop takes place, the embryo has attained full size, the ovary has about completed its enlargement, and the pecans will soon begin to harden. Premature shedding will occur when something affects the embryo. If the embryo aborts after the shell hardens, the nut usually matures, but will be hollow. Commonly called pops. Although the causal factors for embryo abortion are not known, the following situations are considered, by some researchers, to cause embryo abortion: A severe drought or water stress. This is more likely to occur in poor soils and it frequently takes place during the water stage. In Eddy County we used to get most of our rain in July which was at the right time for pecan nut development and supplemented irrigation. With a shift of the rains coming in late August to early September it is coming after pecans started phase II in development. Also rain water being almost pure leaches salts and there by increases the ability of the tree to harvest soil water to be used in nut development. Our irrigation water has salt and because of the it takes more water to leach and less is physiologically available for the tree. I think we need to think about if the rain are not coming in July to increase the frequency or the amount we irrigate at this critical time of the water demand curve of the tree. Conversely prolonged period of excess moisture can be an issue as well. I have made home visits and the grower had left a trickle on their tree 24/7 for months. Lack of air in the soil impairs the root system’s capacity to absorb water and nutrients required by the pecan tree. The tree will have a physiological drought with the same symptoms as lack of water in a saturated soil. Hot, dry winds can increase water loss by increasing the pecan tree moisture requirements due to high transpiration rates. Often the edges of the leaflets will be dead or necrotic because the water evaporation so fast. Insects (shuckworm, southern green stinkbug, pecan weevil). Puncturing of the ovary wall, the future nut shell, will cause nuts to fall in 3 or 4 days. Hail and other physical damages that can disturb the ovary wall (shell) of pecans. Birds and squirrels will often damage nuts causing them to fall. Subscribe to Eddy County Ag news at: http://nmsueddyag.blogspot.com/ Eddy County Extension Service, New Mexico State University is an equal opportunity/affirmative action employer and educator. 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