Effects of pendimethalin and hand weeding on vegetative growth of cowpea accessions.

Abstract

A field study on the effects of pre- and post-emergence application of herbicide (pendimethalin) on the vegetative growth of five accessions of cowpea (TVU-9092, TVU-16265, TVU-16320, TVU-16323 and TVU 16421) was conducted between June and August 2018. Pendimethalin was applied both as pre- and early post-emergence herbicide and followed by two hand weeding at 4 and 8 weeks after sowing (WAS). The cowpea accessions responded differently to the weed control methods. Growth and development increased with the age of cowpea in all the vegetative parameters studied. TVU-16323 produced the highest number of leaves (30, 30) at 4 weeks after sowing respectively in the control cowpea plants. This was followed by (29) in pre-emergence application of herbicide at 0.125 kg/ha for TVU-9092, while the lowest number of leaves was (8.00) in TVU-16265 in the control plants. Plant height was highest (23.17 cm) in TVU-9092 with 0.125 kg/ha post-emergence herbicide application in TVU-9092, followed by TVU-16265 (23.00 cm) with 0.25 kg/ha pre-emergence application, while TVU- 9092 with 0.25 kg/ha pre-emergence application recorded the lowest of the parameter (5.50 cm). Cowpea accession TVU-16265 with 0.25 kg/ha post-emergence herbicide application had the highest leaf area (105.83 cm2 ), followed by TVU-16265 with 0.125 kg/ha pre-emergence application (105.08 cm2 ), while TVU-16421 with 0.125 kg/ha pre-emergence application was the lowest (16.67 cm2). Stem girth was highest in TVU-16421 control plants (9.43 mm), followed by TVU-9092 with 0.125 kg/ha pre-emergence application (9.21 mm), while TVU-16421 with 0.125 kg/ha pre-emergence application recorded the lowest (1.92 mm). Shoot fresh weights were higher in the control plants of TVU-16323 (24.77 g) and TVU-9092 (22.15 g) than in the other treatments. TVU-16320 with 0.250 kg/ha pre-emergence application recorded the lowest shoot fresh weight (1.31 g). Post-emergence application of pendimethalin at 0.125 kg/ha produced the highest shoot dry weight (5.22 g) in TVU-9092, followed by post-emergence application at 0.250 kg/ha in TVU-16421 (4.97 g), while post-emergence application at 0.125 kg/ha in TVU-16421 and the control plants of TVU-9092 had the lowest shoot dry weights of 0.25 g.