Darrell Sparks
Department of Horticulture
University of Georgia
Athens, GA 30602

This season, a major drought occurred in Georgia (Table 1). Except for Camilla, Louisville, Montezuma, and Waycross in May and Tifton in June, rainfall from March to July was below normal. The drought was particularly severe in Cordele, Louisville, and especially in Dawson. The drought affected fruit size; in a non-irrigated orchard, the fruit was about two times smaller than in an irrigated orchard (Fig. 1). Small nut size in non-irrigated orchards has reduced Georgia’s potential production.

Final nut size and shape in non-irrigated orchards varies depending upon the amount of rainfall during the elongation (June to mid July) and expansion (mid July to mid August) stages (Fig. 2). Pecans in areas that had well-distributed rain during elongation and expansion, will produce normal-shaped nuts, though nut size will vary directly with the amount of rain as illustrated for normal and deficit rainfall in Figure 2. If drought was severe during nut elongation but rainfall increased during the expansion stage, the nut will be shorter and rounder than normal. If soil moisture was better during the first half of the expansion period than during the second half, the basal end of the nut will not fully expand and nut shape will be obovate, i.e., the tip is broader than the base. Thus, at nut maturity, the size and shape of the nut will reflect the soil moisture history that existed during the two stages of nut sizing.

In non-irrigated orchards and assuming 1.5 or more inches of rain in late August and into the first half of September (Sparks, 2001), kernel quality should be very good for two reasons. One, a small nut fills with kernel better than a large nut (Sparks, 2001) and two, the detrimental effect of scab (Cole, 1947) will be minimal due to low scab infections associated with drought conditions. If soil moisture is very good during kernel development, the shells of drought induced small nuts may occasionally crack open during the latter stage of kernel filling. If so, the occurrence will be due to a nut volume that is too small to contain the kernel.

Literature Cited

Cole, J. R. 1947. Spraying to control pecan scab on the Schley and Moore varieties - Albany, Georgia and Monticello, Florida. Proc. Southeastern Pecan Growers Assn. 40:62-70.

Sparks, D. 2001. Managing pecan nut growth. Proc. Southeastern Pecan Growers Assn. 94:120-147.

Fig. 1. Stuart fruit from a sprinkler-irrigated (A) and a non-irrigated (B) blocks in the same orchard. Fruit weight from sprinkler-irrigation block was 11.1 g; fruit weight from non-irrigated block was 5.5 g. Fruit from Graham Pecan Farm, Leary, Ga. were collected and weighted on July 26, 2006.

Fig. 2. Diagrammatic representation of the effect of rainfall (non-irrigated orchards) during nut elongation (June - July 15) and expansion (July15-August 15) on nut shape and size.