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Herbicide-Resistant Corn for Reducing Use of Residual Herbicides and for Wirestem Muhly Control 1998

Project Leader: Russ Hahn

Objectives:

1. Determine and compare the effect on weed control and silage corn yields of

    1. various application times with Roundup Ultra in Roundup-ready (RR) corn
    2. various application times with Liberty in glufosinate-resistant (GR) corn
    3. a standard pre-emergence (PRE) control program

2. Demonstrate the potential value of Roundup Ultra and Liberty herbicides with RR corn and GR corn, respectively, for wirestem muhly control.

Results:

With moderate weed pressure in the Roundup Ultra and Liberty experiments there were few significant differences in weed control or silage corn yields. Good to excellent control of most annual weeds was achieved with all treatments in the RR corn. Velvetleaf control averaged only 63% with the mid-postemergence applications of Liberty alone or in combination with atrazine but averaged 97% with the PRE standard.

With severe weed pressure from common ragweed in a second pair of experiments, application timing of Roundup Ultra and Liberty treatments had a significant impact on yields. Higher yields were achieved with the PRE standard in both RR and GR corn. Common ragweed control was good to excellent with all but one of the Roundup Ultra and the Liberty treatments, and all but that one treatment exceeded the control achieved by the PRE standard. These results clearly demonstrate the importance of timely application when using low-residual, total postemergence weed control programs.

Roundup Ultra treatments were less effective against wirestem muhly in Madison County than in Chenango County. This has been attributed to the very rough seedbed following reduced tillage in Madison County. In Chenango County all of the Roundup Ultra treatments provided good to excellent wirestem muhly control, ranging from 93 to 100% on July 24. There were no significant differences in silage corn yields among these treatments due to the moderate wirestem muhly infestation