1. Dep. of Soil and Crop SciencesTexas A&M Univ.College StationTX77843‐2474
2. Texas Agric. Exp. Stn.Texas A&M Univ. SystemStephenvilleTX76401
3. Texas A&M Univ. SystemPlant Dis. Res. StnYoakumTX77995
4. USDA‐ARS Plant Science and Water Conservation LaboratoryStillwaterOK74076