The 2005 growing season was not good for pecan production in Georgia. The cool weather during March and April resulted in late nut maturity (Sparks, 2005) which delayed entry into the early market. Fruit set was excessive, especially on Stuart. Rains were frequent and above normal which created two problems. 1) Fruit scab was difficult to control because of the frequent rain. In June and July (the major fruit scab months) the number of days with rains was 18 and 19 which were respectively 10 and 9 days above the 40-year norm. Additionally, rain occurred on 23 days in August which was 16 days above the 40-year norm. 2) The volume of precipitation during June, July, and August 1-15 (major nut sizing period) was 8.3, 8.7, and 3.4 inches, respectively. Therefore, 42% of Georgia’s annual precipitation fell during this 10-week period. The abundant rain resulted in a large nut size. Large nuts are more difficult to fill with kernel than small nuts especially when fruit set is high (Sparks, 2002) as in 2005. September, the major period of kernel filling, was unusually dry (National Climatic Data Center, 2005). Low rainfall in September was not a problem in well-irrigated orchards but it was a major problem in dryland orchards and orchards with marginal drip systems as soil moisture was inadequate to fill the nut (Sparks, 1992) and maintain tree vigor (Sparks, 2003). Shuck decline (Sparks et al., 1995) was a problem in orchards with limiting soil moisture in September. All of these factors resulted in below average kernel quality in Georgia, especially so in Stuart. Mites and black aphids also were serious problems. Considerable defoliation occurred before the nuts matured in abandoned orchards and on roadside and yard trees. In commercial orchards, defoliation was less but occurred to varying degrees.
Fruit scab was a major problem. Almost all orchards had scab. In some orchards, the crop was lost to scab during rapid fruit expansion. The difference among other orchards was in the degree of scab control. A substantial portion of Georgia’s potential crop was lost to scab, either due to a reduction in kernel quality or to nonmarketable nuts.
In open orchards, fruit scab control was almost invariably better in the lower than in the upper canopy, indicating a widespread failure to delivery sufficient fungicide to the top of the tree. Thus, in well managed open orchards, quality and subsequent production losses from scab were primarily due to inadequate control in the upper canopy. In tight or overcrowded orchards (identified by absence of grass due to shading), scab control and quality were very poor throughout the canopy regardless of other cultural practices. Scab is essentially impossible to control in a tight orchard during a wet season. This is because the foliage and fruit are slow to dry (due to poor sunlight and poor air movement) following a rain, extending the period the leaves and fruit are wet. Often the foliage and fruit in tight orchards do not dry between frequent rains, a situation that acts as incubator for scab.
The importance of air movement and sunlight on scab control on the fruit is very pronounced. For example, scab was devastating in a tight Desirable orchard, however, on isolated trees growing in open spots in the same orchard, scab control was relatively good. In addition, scab control on Desirable trees with an open canopy in the same orchard much better than on trees with a more closed canopy.
In open orchards, large overhanging, low limbs blocked the fungicide spray and prevented it from reaching the upper canopy. Scab control was good on the blocking limbs but poor above the blocking limb. Scab control also varied with topography. Scab control was worse when an orchard or a portion of an orchard was situated in a low area than when situated on a ridge. Inferior scab control resulted because air drainage is inherently poor in low areas.
None of the observations on scab discussed above are new. They are readily observed during any season with an excessive number of rains as in 2005.
As with scab control, inadequate spray coverage in the upper canopy, large overhanging limbs, and tight orchards result in poor mite control. Such was evident during 2005.
Failure to delivery sufficient fungicide to the top of the tree results from too fast sprayer speed, spraying during windy conditions, insufficient pressure, improper nozzles and nozzles positioning, blocking limbs, a tight orchard, or, trees that are simply too tall for the capacity of the sprayer. Marketable production will increase with improved coverage of the upper canopy. Likewise, marketable production of the tree will increase if low, blocking limbs are removed. Tight orchards require tree removal if scab is to be controlled during wet seasons. Low areas are a perennial problem in wet years illustrating the importance of selecting orchards sites with good air drainage. Scab in these spots is lessened by maintaining a very open orchard.
In some orchards, fruit scab on Stuart was worst than on Schley, a situation first observed in Perry, Georgia about 5 years ago. Historically in Georgia, scab has been worst on Schley than on Stuart. The apparent increased susceptibility of Stuart to scab underlines the significance of the continuing evolution of the scab organism and that scab resistance in a cultivar is seldom long-term.
In addition to the devastating effect of scab on kernel quality, an excessive crop load, especially on Stuart, took its toll. Quality in a well managed, sprinkler-irrigated Stuart orchard in which the fruit had been mechanical fruit thinned was substantially better than in a similar Stuart orchard without thinning. Likewise, quality was also good in a well-irrigated, open Stuart orchard with a moderate fruit load. Nut quality was very poor in dryland and marginally-irrigated Stuart orchards with an excessive crop load. In these orchards, the effect of an excessive crop load was compounded with the induction of shuck decline. Shuck decline is not a disease (Sparks et al., 1995); it is induced by stress of excessive fruiting that is accentuated by shading in tight orchards and by inadequate soil moisture in September. Shuck decline results in poor quality kernels because the shuck begins to decline or die before the kernel is mature. Under similar culture, Schley nut quality was better than Stuart which reflects a smaller nut size and lighter crop on Schley. Stuart remains a major cultivar in Georgia. Until mechanical fruit thinning of Stuart becomes widespread, Georgia production will alternate with the “on” and “off” fruiting cycle of Stuart.
Although 2005 was submarginal for nut production, it was ideal for the growth of young, nonbearing trees, assuming leaf scab was controlled. Shoot elongation was outstanding. The excellent shoot elongation was probably enhanced by the reduction in temperature associated with the numerous rains. Repeated observations indicate that reduction in temperature associated with rain results in continued shoot elongation or, if shoot elongation has ceased, a second cycle is induced. Rate and duration of shoot elongation are significant because the time a pecan tree comes into production is largely a function of how fast the tree grows, rather than how many years it has been planted (Ware and Johnson, 1957).
Relative to 2005, return bloom in 2006 will be reduced in many Georgia orchards. The reduction will occur because of excessive fruiting (especially Stuart), excessive rain (Sparks, 1996), premature defoliation from mites and black aphids (Moznette, 1934), and, in dryland orchards and orchards with marginal drip irrigation systems, from the September drought (Sparks, 1996). Return bloom will be best in orchards in which excess fruit was removed by mechanical fruit thinning, soil moisture was nonlimiting in September, and healthy leaves where retained until frost.
Literature Cited
Moznette, G. F. 1934. Experiments in control of pecan black aphids under orchard conditions. Proc. S. E. Pecan Growers Assn. 28:55-61.
National Climatic Data Center. 2005. Climatological data for Georgia. Natl. Oceanic Atomospheric Admin., Asheville, N. C.
Sparks, D. 1992. Pecan cultivars - The orchard’s foundation. Pecan Production Innovations, Watkinsville, Ga.
Sparks, D. 1996. A climatic model for pecan production under humid conditions. J. Amer. Soc. Hort. Sci. 121:908-914.
Sparks, D. 2002. The influence of topography, crop load, and irrigation on pecan nut volume and percentage kernel. Annu. Rpt. Northern Nut Growers Assn. 93:87-92.
Sparks, D. 2003. Pecan tree dieback following 1999-2002 drought associated with September rainfall. J. Amer. Pomol. Soc. 75:142-146.
Sparks, D. 2005. Nut maturity in southwest Georgia is estimated to be late in 2005. The Pecan Grower. 17:14.
Sparks, D., W. Reid, I. E. Yates, M. W. Smith, and T. G. Stevenson. 1995. Fruiting stress induces shuck decline and premature germination in pecan. J. Amer. Soc. Hort. Sci. 120:43-53.
Ware, L. M. and W. A. Johnson. 1957. The effect of cultural and fertilizer practices on the nitrate and moisture levels and on growth of young pecan trees. Proc. S. E. Pecan Growers Assn. 50:39-50.