Pecan orchards in the southeastern United States are often found growing adjacent to fields of annual row-crops. There can be multiple advantages and/or disadvantages to this situation for both crops. The roots of mature pecan trees can extend to a length twice the width of the tree canopy (Hammar et al., 1953; Woodroof and Woodroof, 1934). Pecan tree roots extending into an adjacent row crop field can compete with the row crop for available soil water and nutrients (Allen et al., 2004a, 2004b; Diomides et al., 2006; Wanvestraut et al., 2004). To date, most studies on the effects of interactions between pecans and row crops have focused solely on the row crop.
Pecans and peanuts are highly valuable to agricultural profitability in the southeastern United States. When combined, these crops account for over $510 million in farm gate value for Georgia alone (McKissick and Boatright, 2007). Pecans and peanuts may also be grown in close proximity in Alabama, Florida, Oklahoma, and Texas. Due to the importance of these crops to agriculture in these areas and their often close proximity to each other, it is important that the production practices of both crops be compatible.
A persistent problem was identified in pecan orchards throughout southern Georgia in which pecan trees growing in rows immediately adjacent to peanut fields developed hollow pecans. In-shell nut size and appearance was normal; however, the kernels failed to develop (Fig. 1). Frequent observations in multiple orchards suggested that this problem only occurred where peanuts were planted adjacent to pecan orchards. It was never observed in orchards adjacent to other row crops. One additional case was observed in a row of pecan trees adjacent to a highway right-of-way.
Imazapic is a popular postemergence herbicide used in peanut fields early in the growing season to control various broadleaf weeds, grasses, and sedges (Grichar and Nester, 1997; Richburg et al., 1996; Webster et al., 1997). Imazapic is rapidly absorbed by plant roots and shoots, transferred to other parts of the plant, and accumulates in actively growing tissues (Shaner and Singh, 1998). Due to its soil residual activity, imazapic has long rotation restrictions before subsequent crops can be planted (Grymes et al., 1995; Matocha et al., 2003; York et al., 2000). Imazapic is also frequently used in weed management programs along highway right-of-ways.
Due to its wide-scale use in peanut fields and right-of-ways, it was suspected that imazapic was a potential cause of the “hollow pecans” described above. The objective of this study was to investigate the effect of imazapic on pecan production.
Allen, S., Jose, S., Nair, P.K.R., Brecke, B.J., Nkedi-Kizza, P. & Ramsey, C.L. 2004a Safety net role of tree roots: Evidence from a pecan-cotton alley cropping system in the southern United States For. Ecol. Mgt. 192 395 407
Allen, S., Jose, S., Nair, P.K.R., Brecke, B.J., Nkedi-Kizza, P. & Ramsey, C.L. 2004b Competition for 15N-labeled fertilizer in a pecan-cotton alley cropping system in the southern United States Plant Soil 263 151 164
Diomides, S.Z., Shibu, J., Nair, P.K.R. & Ramsey, C.L. 2006 Interspecific competition in a pecan-cotton alleycropping system in the southern United States: Production and physiology Can. J. Bot. 84 1686 1694
Fletcher, J.S., Pfleeger, T.G. & Ratsch, H.C. 1993 Potential environmental risks associated with the new sulfonylurea herbicides Environ. Sci. Technol. 27 2250 2252
Grichar, W.J. & Nester, P.R. 1997 Nutsedge (Cyperus spp.) control in peanut (Arachis hypogaea) with AC 263,222 and imazethapyr Weed Technol. 11 714 719
Grymes, C.F., Chandler, J.M. & Nester, P.R. 1995 Response of soybean (Glycine max) and rice (Oryza sativa) rotation to AC 263,222 Weed Technol. 9 504 511
Hammar, H.E., Smith, C.L. & Alben, A.O. 1953 Boron uptake as a criterion of the root spread of pecan trees Proc. Amer. Soc. Hort. Sci. 62 131 134
Jenkins, S.R., Wehtje, G.R., Morgan, J.M., Bollinger, A.F. & Young, D.G. 2000 Temperature effects of atrazine and imazapyr on soils Water Air Soil Pollut. 118 169 178
LaRossa, R.A. & Schloss, J.V. 1984 The sulfonylurea herbicide sulfometuron is an extremely potent and selective inhibitor of acetolactate synthase in Salmonella tryphimurium J. Biol. Chem. 259 8753 8757
Magels, G. 1991 Behavior of the imidazolinone herbicides in soil: A review of the literature 191 209 Shaner D.L. & O'Connor S.L. The imidazolinone herbicides CRC Press Boca Raton, FL
Matocha, M.A., Grichar, W.J., Senseman, S.A., Gerngross, C.A., Brecke, B.J. & Vencill, W.K. 2003 The persistence of imazapic in peanut (Arachis hypogaea) crop rotations Weed Technol. 17 325 329
McKissick, J.C. & Boatright, S.R. 2007 2007 Georgia farm gate value report 27 Oct. 2009 <http://commodities.caes.uga.edu/turfgrass/georgiaturf/Publicat/PCRP2009/FarmGate.pdf>.
Richburg J.S. III, Wilcut, J.W., Colvin, D.L. & Wiley, G.R. 1996 Weed management in Southeastern peanut (Arachis hypogaea) with AC 263,222 Weed Technol. 10 145 152
Shaner, D.L. & Singh, B.K. 1998 Why are imidazolinones such potent herbicides 23 29 Baker D.R. Synthesis and chemistry of agrochemicals. ACS Symposium Series 686 American Chemical Society Washington, DC
Stougaard, R.N., Shea, P.J. & Martin, A.R. 1990 Effect of soil type and pH on adsorption, mobility, and efficacy of imazaquin and imazethapyr Weed Sci. 38 67 73
Wanvestraut, R.H., Jose, S., Nair, P.K.R. & Brecke, B.J. 2004 Competition for water in a pecan-cotton alley cropping system in the southern United States Agrofor. Syst. 60 167 179
Webster, T.M., Wilcut, J.W. & Coble, H.D. 1997 Influence of AC 263,222 rate and application method on weed management in peanut (Arachis hypogaea) Weed Technol. 11 520 526
York, A.C., Jordan, D.L., Batts, R.B. & Culpepper, A.S. 2000 Cotton response to imazapic and imazethapyr applied to a preceding peanut crop J. Cotton Sci. 4 210 216