Darrell Sparks
Department of Horticulture
University of Georgia
Athens, Georgia 30602
Blocks within an orchard or the entire orchard may have less than an economical production in some years; that is, the potential production is too low to cover the cost of a full cultural program. The result is a net lost for the year. In such situations, the objective is to minimize financial loss by reducing cultural inputs as much as possible without reducing next year's production. In fact, a full cultural program during the off year may increase fruiting the following year to the point that acceptable quality is not produced unless mechanical fruit thinning is employed. Excessive fruiting the year following a very low crop is common. Thus, a reduced cultural program, especially nitrogen application, during the off year may be beneficial with respect to nut quality in the following year.
Evaluating potential production cannot be made until the first drop (pistillate flowers) has been completed. This drop occurs 7-10 day following full bloom which in Georgia is about mid-May. The first drop is usually the critical drop for most cultivars. Potential fruit production is more or less fixed once the first drop occurs as fruit loss from the subsequent second, third, and fourth drop is minor. Exceptions are Desirable and Forkert, which characteristically have a very large second drop. Nevertheless, fruit set and potential production can be evaluated following the first drop in most situations.
Generally, fruit set on low limbs is a good indicator for the tree as a whole. Usually, a tree with poor fruit set low limbs will also have poor fruit set on limbs throughout the tree canopy. However, this rule is not universal as Stuart trees sometimes have a poor "bottom" crop and a better "top" crop. Also, in a crowded orchard, the top crop is most often better than the bottom crop. For these reasons, some growers use a lift to evaluate the crop in the upper portion of the tree. Evaluation of fruit set is further complicated in orchards with mixed cultivars which is often the case in Georgia. In a mixed orchard of Desirable, Schley, and Stuart, fruit set following a stressful year is usually best on Desirable, intermediate on Schley, and almost invariably worse on Stuart. If the cultivars are planted by row, evaluation of fruit set and subsequent culture can be made by cultivar. However, if the cultivars are "jumbled up," as often is the case, an average estimate must be made.
Growers and others have used various methods for estimating potential production in May. However, estimates based on a grower's previous observations of fruit set and orchard performance appears to be the best. Most growers have a visual image of an optimum fruit set and the production per acre associated with this fruit set. The estimate of fruit set should be made as a percentage of an optimum observed in previous years. This estimate, when multiplied by the maximum or near maximum production produced in previous years, will give an approximation of the potential production for the current year. Value of this crop, based on typical price per pound, when compared to average production cost will determine if a full cultural program would be profitable.
Estimating fruit set is easy if there is no or little fruit set or if fruit set is very high. The problem is with intermediate fruit set. There is always the chance that production is better than estimated and a crop will be judged to be non-profitable when it is profitable. Within the last few years, some Georgia growers have used a May estimate of fruit set to determine the level of culture to be employed. When fruit set has been low, the strong tendency has been to over estimate fruit set which no doubt reflects the optimistic nature of pecan growers. Furthermore, as the fruit begins to increase in size, the low crop erroneously "looks better" and the original estimate of fruit set is increased. During the 1995 season, a May estimate of fruit set was made in an orchard that was on the off cycle. The consensus was that the profitability of the orchard was questionable. The decision was delayed until the fruit became readily visible. The fruit set was judged to be higher at the second estimate than in May. A full culture program was continued. Final production at 300 pounds per acre was way below the economic threshold for production. Other managers also made the same mistake of revising May estimates and continuing full management. These orchards, likewise, did not produce a crop sufficient to cover operation cost.
Employment of cultural practices based on May fruit was successfully applied in 1994. In one 500-acre orchard, fruit set was very poor in the Stuart blocks, fair in the Schley blocks, and good in the Desirable blocks. Cultural practices were discontinued in the Stuart blocks in late May. Full culture was maintained in the Schley and Desirable blocks. The grower made a small profit from the 100 acres of Schleys and Desirables. If full culture had been maintained in the Stuart blocks, a major loss would have occurred. Production of all cultivars in this orchard was outstanding in 1995.
The following may serve as a guide for culture during an off-cycle of production. The objective is to keep the leaf efficient in order to have an optimum return bloom. The guide assumes that once the decision is made that fruit set is not economical, the fruit will be sacrificed.
Fertilization: Some growers apply fertilizer in split applications. About one-half of the recommended rate is applied in March (non- and drip-irrigated orchards) or early April (sprinkler-irrigated orchards). The remainder is applied in May. Split application is well suited for decision-making based on fruit set. If fruit set is judged not to be economical in mid-May, do not apply the remaining one-half of the fertilizer. An exception would be in cases where the fertilizer is being applied to correct a major deficiency. In such a case, apply the full recommendation for that nutrient(s).
Fungicides: Once the leaf has matured, it is no longer susceptible to scab. Leaves on old trees are mature by late May. Do not apply fungicides after the third week in May. If the growing season is wet in June, a second flush of growth sometimes occurs on old trees. This new growth will scab if environmental conditions are conducive for scab. However, in most cases, new growth is sparse and loss in leaf efficiency from scab for the tree as a whole is minor.
Downy spot can cause massive premature defoliation, especially on Stuart. Because of the threat of massive defoliation, downy spot can be a much worse disease than scab. If fungicides are applied for scab through the third week of May as suggested above, downy spot will also probably be controlled. However, scouting for downy spot should continue throughout the season. Should downy spot become a problem, research and grower experience have shown that one spray of six ounces of Orbit per acre to be effective in arresting the disease.
Zinc sprays: Zinc deficiency occurs only during the period of leaf expansion. In this aspect, zinc deficiency is similar to scab which also occurs only on expanding leaves.
For this reason, terminate zinc sprays after the third week of May as suggested for scab sprays. If a second cycle of shoot growth occurs in June-July, the new growth will be susceptible to zinc deficiency, However, the deficiency will be relative minor because the second cycle is usually sparse.
Insecticides: Use insecticides only against insects that can cause defoliation. In most seasons, the major defoliating insect is black aphid. Mites, which can likewise cause massive defoliation, should also be carefully monitored. Similarly, serpentine leaf minors should be carefully monitored. Do not spray for yellow aphids.
Soil moisture: Do not irrigate unless there is a prolonged drought. Do not mow. In non- irrigated orchards, discontinue the herbicide strip. In case irrigation is needed, maintain a narrow strip along the emitter strip and, in sprinkler orchards, keep the strip just wide enough to prevent weeds and grass from interfering with the sprinkler head.
Reducing cultural inputs during an off season has a risk other than the possibility of under estimating the mid-May fruit set. The risk is that the price per pound may be abnormally high, making an otherwise unprofitable crop profitable. Abnormally high prices occur if the national crop is extremely off. Such was the case during 1992 when Georgia's production was at a 28-year low. However, there is usually an indication by bloom time as to whether or not the national production is expected to be abnormally low. Nevertheless, some risk remains as the national crop may be drastically reduced in some regions by adverse climate that occur after mid-May.
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