Development and evaluation of practical control action indicators in corn weed management

The different handweeding schedules brought about different levels of weed pressure as shown by significant differences in relative crop fresh weight (RCFW), relative crop density (RCD) (actual counts), RCD (Visual estimates), relative crop cover (RCC), exposed crop leaf area (ECLA), and relative weed height (RWH) at 15, 30, and 45 DAS. The major weed species in the first experiment were Cleome rutidosperma DC, Rottboellia cochinchinensis (Lur.) W.D. Clayton, Cyperus rotundus L., Amaranthus spinosus L., Commelina benghalensis L., Ipomoea triloba L., and Portulaca oleracea L. In the second experiment, the major weed species were R. cochinchinensis, C. rotundus, C. rutidosperma, I. triloba, C. benghalensis, Murdania nudiflora (L.) Brenan, and Celosia argentea L. Regression and correlation analysis using the logarithmic model y=a + b log x failed to show any correlation between yield and the different parameters at the three sampling dates because of insufficient weed pressure and the relatively high competing ability of the corn crop. Grains yield obtained from treatment 5 (HW 6X at 5, 10, 15, 20, 25, 30 DAS) did not differ significantly from the unweeded treatment. The weed control action indicators tested in the second experiment were based on the appropriate parameters from Treatment 5. In the second experiment, the highest grain yield (3.74 t/ha) was obtained from plots which received five calendar handweeding treatments (treatment 8). No grain yield was obtained from the unweeded plot. All the indicator-based weed management systems except those on RWH required the control action of handweeding 3X (15, 30, and 45 DAS) for the whole season, and gave grain yield comparable with calendar handweeding-based treatments (5X, 4X, 3X, 2X) and the two selected farmers' practices. The results indicate that weed control action indicators developed under low weed pressure for a very competitive crop like corn served as useful tools in weed management even under high weed pressure. The lowest total labor requirement and consequently the highest labor reduction in labor requirement for weed management were obtained from the two selected farmers' practices, followed by calendar HW 2X (HW 14 and 28 DAS) and weed management based on RWH (HW15 AND 45 DAS)