Effects of Shielded Spray of Paraquat and Glyphosate on the Growth and Yield of Corn (Zea mays L.)

Abstract

Field experiments were conducted in the fall crop of 1990 and the spring crop of 1991 to evaluate growth and yield of corn (Zea mays L. cv. Tainung No.1) in responses to paraquat and glyphosate, with or without shielding, applied at three different times in the vegetative stage. Although weed control was improved, herbicide applications at 2, 4 or 6 weeks after planting (WAP) slightly reduced corn growth and yield relative to those of handweeding treatments, but higher than the weedy check. Without proper shielding, the growth and yield of corn was further decreased due to plant injury. Compared to the shielded ones, plant height and leaf area of unshielded corn plants at the 50% silking were declined more than 10% and 20% by paraquat and 15% and 25% by glyphosate applied at 2, 4 or 6 WAP in both 1990 and 1991. Whereas, more than 50% and 60% corn yield reductions were found by applications of paraquat and glyphosate, respectively, in the two seasons. When analyzing the yield characters, it was shown that, without shielding, ear weight and kernel weight were decreased in the spring crop. The effective plant percentage (EPP) was affected by herbicide applications, especially under unshielded conditions. Weed control practices applied as early as 2 WAP ensuing uniform tasseling and silking while glyphosate lengthened the 50% tasseling and silking dates when applied without shielding before 4 WAP. It is therefore suggested that applications of paraquat and glyphosate, if necessary, in the corn field should be with proper shieldings to eliminate corn injury. Paraquat, 1,1'-dimethy 1-4, 4'-bipyridinium dichloride glyphosate;N-(phosphonomethyl) glycine