Georgia is the largest pecan producer in the United States (U.S. Department of Agriculture, 2009). The coastal plain soils on which most Georgia pecan orchards are established are inherently low in S. In addition, available S leaches readily through the soil profile of the region’s loamy sand soils. As a result, S availability does not appear adequate for many southeastern U.S. pecan orchards (Wells, 2009).
Soil S may be immobilized by a variety of factors, including soil organic matter, temperature, moisture, and soil pH. Since the early 1980s, atmospheric S depositions have declined drastically after the enforcement of Clean Air Acts. This led to S deficiency becoming a major nutritional disorder in western Europe (Haneklaus et al., 2003). Leaf elemental S was deficient in almost 90% of Georgia pecan orchards in a recent survey using 0.25% as the minimum leaf sufficiency concentration (Wells, 2009). Average leaf S was below the recommended leaf sufficiency range for S in both years of the study. However, Smith et al. (2012) have suggested a minimum sufficiency concentration of 0.20% for pecan, which may be a more realistic goal for Southeastern pecan orchard conditions. An insufficient plant supply of S has been shown to reduce crop productivity, diminish crop quality, affect plant health, and impair N use efficiency (Barker and Pilbeam, 2007).
The role of S in helping to manage plant disease has been investigated for centuries. Recently, the concept of sulfur-induced resistance was developed to explain an increased resistance of various crops to fungal pathogens with S fertilization (Bloem et al., 2005). Elemental S has been used as a fungicide in viticulture, arboriculture, and in cereal crops (Legris-Delaporte et al., 1987). Elemental S-based fungicides have been used for many decades to control peach scab, Fusicladosporium carpophilum (Partridge and Morgan-Jones) in southeastern U.S. commercial peach orchards (Schnabel et al., 2007). The effects of elemental S on pecan scab have been studied since the 1920s; however, most studies have demonstrated little effect of S on pecan scab Fusicladium effusum G. Winter (Bertrand et al., 1981; Waite, 1924).
Foliar urea sprays are known to enhance fruit production in a variety of tree fruit crops (Johnson et al., 2001; Lovatt, 1999; Rosecrance et al., 1998). Many commercial pecan producers in Georgia routinely spray foliar urea in combination with their fungicide sprays. Urea can be absorbed rapidly and efficiently by the leaves of most crop plants (Johnson et al., 2001); however, aside from its effect on the enhancement of zinc uptake by pecan leaves (Smith and Storey, 1979), very little information is available in the scientific literature regarding the effect of foliar urea sprays on pecan production.
The objectives of this study were to investigate the effects of foliar application of elemental S and urea on pecan leaf tissue N and S concentration, pecan nut quality, LCI, and pecan scab control.
Alben, A.O. 1957 Results of an irrigation experiment on ‘Stuart’ pecan trees in east Texas in 1956 Proc. Texas Pecan Growers Assn. 36 16 23
Barker, A.V. & Pilbeam, D.J. 2007 Handbook of plant nutrition. Taylor and Francis Group, New York, NY
Bertrand, P.F., Littrell, R.H. & Gottwald, T.R. 1981 The effect of foliar applied sulfur on pecan production Proc. Southeastern Pecan Growers Assn. 74 187 191
Bloem, E., Haneklaus, S. & Schnug, E. 2005 Significance of sulfur compounds in the protection of plants against pests and diseases J. Plant Nutr. 28 763 784
Clarkson, D.T., Saker, L.R. & Purves, J.V. 1989 Depression of nitrate and ammonium transport in barley plants with diminished sulphate status: Evidence of coregulation of nitrate and sulphate intake J. Expt. Bot. 40 953 963
Dutcher, J.D., Wells, M.L., Brenneman, T.B. & Patterson, M.G. 2010 Integration of insect and mite, disease with weed management to improve pecan production, p. 133–162. In: Ciancio, A. and K.G. Mukerji (eds.). Intergrated management of arthropod pests and insect borne diseases. Springer Publishing, Dordrecht, The Netherlands
Haneklaus, S., Bloem, E. & Schnug, E. 2003 The global sulphur cycle and its link to plant environment, p. 1–28. In: Abrol, Y.P. and A. Ahmad (eds.). Sulphur in plants. Kluwer Academic Publishers, Dordrecht, The Netherlands
Hu, H. & Sparks, D. 1992 Nitrogen and sulfur interaction influences net photosynthesis and vegetative growth of pecan J. Amer. Soc. Hort. Sci. 117 59 64
Hudson, W., Brock, J., Culpepper, S. & Wells, L. 2012 Georgia pecan pest management guide. Univ. Georgia Coop. Ext. Bull. 841
Johnson, R.S., Rosecrance, R., Weinbaum, S., Andris, H. & Wang, J. 2001 Can we approach complete dependence on foliar-applied urea nitrogen in an early maturing peach J. Amer. Soc. Hort. Sci. 126 364 370
Klein, I. & Weinbaum, S.A. 1985 Foliar application of urea to almond and olive: Leaf. retention and kinetics of uptake J. Plant Nutr. 8 117 129
Legris-Delaporte, S., Ferron, F., Landsy, J. & Costes, C. 1987 Metabolization of elemental sulfur in wheat leaves consecutive to its foliar application Plant Physiol. 85 1026 1030
Loh, F.C.W., Grabosky, J.C. & Bassuk, N.L. 2002 Using the SPAD 502 meter to assess chlorophyll and nitrogen content of Benjamin fig and cottonwood leaves HortTechnology 12 682 686
Magness, J.R. 1955 Practicability of irrigating pecan orchards in southeastern states Proc. Southeastern Pecan Growers Assn. 48 23 29
Reuveny, Z., Dougall, D.K. & Trinity, P.M. 1980 Regulatory coupling of nitrate and sulfate assimilation pathways in cultured tobacco cells Proc. Natl. Acad. Sci. USA 77 6670 6672
Rosecrance, R.C., Johnson, R.S. & Weinbaum, A. 1998 The effect of timing of post-harvest foliar urea sprays on nitrogen absorption and partitioning in peach and nectarine trees J. Hortic. Sci. Biotechnol. 73 856 861
Schnabel, G., Layne, D.R. & Holb, I.J. 2007 Micronised and non-micronised sulphur applications control peach scab equally well with negligible differences in fruit quality Ann. Appl. Biol. 150 131 139
Scott, N.M., Dyson, P.W., Ross, J. & Sharp, G.S. 1984 The effect of sulphur on the yield and chemical composition of winter barley J. Agr. Sci. 103 699 702
Seeman, J.R., Sharkey, T.D., Wang, J. & Osmond, C.B. 1987 Environmental effects on photosynthesis, nitrogen-use efficiency and metabolic pools in leaves of sun and shade plants Plant Physiol. 84 796 802
Smith, M.W., Rohla, C.T. & Goff, W.D. 2012 Pecan leaf elemental sufficiency ranges and fertilizer recommendations HortTechnology 22 594 599
Smith, M.W. & Storey, J.B. 1979 Zinc concentration of pecan leaflets as influenced by zinc source and adjuvants J. Amer. Soc. Hort. Sci. 104 474 477
Stein, L.A., McEachern, G.R. & Storey, J.B. 1989 Summer and fall moisture stress and irrigation scheduling influence pecan growth and production HortScience 24 607 611
U.S. Department of Agriculture 2009 2007 census of agriculture. Natl Agri. Stat. Ser., Washington, DC
Waite, M.B. 1924 Comparison of orchard and nut diseases and their control by spraying fungicides Proc. Nat. Pecan Growers Assn. 23 48 58
Wells, M.L. 2009 Pecan nutrient element status and orchard soil fertility in the southeastern United States coastal plain HortTechnology 19 432 438
Wells, M.L., Conner, P. J., Funderburk, J. F. & Price, J. G. 2008 Effects of foliar-applied boron on fruit retention, fruit quality, and tissue boron concentration of pecan HortScience 43 696 699
Yousseffi, F., Weinbaum, S.A. & Brown, P.H. 2000 Regulation of nitrogen partitioning in field-grown almond trees: Effects of fruit load and foliar nitrogen applications Plant Soil 227 273 281