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

Fig. 1. Nut maturity date of pecan in the Dougherty-Crisp counties area of southwest Georgia as a function of heat units (base 65 0F) in March plus April. The equation for the relationship is Y = 295.12 - 0.1086X.

Time of nut maturity in Georgia is dependent on heat accumulated during March and April. Temperature alters the time of budbreak and subsequent rate of shoot elongation that, in turn, affects the time of stigma receptivity. Consequently, the temperature effect on date of nut maturity is indirect in that springtime temperatures influence the starting date of fruit development. Cool springs delay the starting date; warm springs advance it. Once the stigma is receptive, the time to fruit maturity is essentially constant for a given cultivar.

The relationship between date of nut maturity and heat accumulation in March and April is close and, thus, can be used to predict nut maturity in pecan (Fig. 1). This season’s average heat accumulation in the Dougherty - Crisp counties’ area was 94 heat units. The predicted date for 2008 is October 11 which is the 285 th day of the year. The predicted nut maturity date for 2008 is 7 days later than the maturity date in 2007.

Nut maturity in Figure 1 is the definition used for early harvest: that is, the shuck has dehisced and is completely separated from the shell, but is still green. The shell has turned brown with natural markings developed. At this stage of maturity, some nuts on cultivars with staggered nut maturity, mainly Stuart, will require mechanical dehulling. Mechanical drying of the nuts is required following harvest. The stage of nut maturity described is earlier than most growers prefer to harvest, but, nevertheless, it is a definable reference stage of maturity. For the individual grower, the estimated nut maturity date for 2008 can best be utilized by adding 7 days to the starting harvest date for 2007.

In years in which Schley breaks buds before Stuart, as occurred this Spring, the predicted date of nut maturity will be closer to actual nut maturity of Schley than that of Stuart. Nut maturity of Stuart in 2008 is expected to be after that of Schley. Observations indicated that pecan shoot development in Athens was about 5 days later than in the Dougherty - Crisp counties’ area. Thus, the date of nut maturity is expected to be progressively later from south to north Georgia.

See http:www.geocities.com/CollegePark/Campus/3370 for this and other pecan information.