Comparison of Preemergence and Postemergence Weed Control Systems in Newly Established Pecan

Six weed control programs with and without irrigation were investigated in a newly established pecan orchard. Irrigation increased crown diameter growth in only one of seven growing seasons but increased nut yield an average of 35% in the first two bearing years. Weed control program significantly influenced crown diameter beginning in the fourth growing season and continued through season six while also impacting final crown diameter. The use of postemergence (POST) herbicides increased crown diameter a minimum 4 mm vs. preemergence (PRE) herbicides. Mowing neither increased nor decreased crown diameter when used with herbicides; however, when used solely, crown diameter was 29% less. Highest growth rates were obtained with a combination PRE plus POST weed management system. Nut yields were closely linked to growth data. No differences in nut yield were observed between PRE- or POST-herbicide programs alone or in combination with mowing. Mowing alone decreased nut yield 57% vs. herbicide-based approaches...