Trends in Herbicide Use On Roadside Rights-of-Way in Oklahoma.

The Oklahoma Department of Transportation (ODOT) utilizes an integrated vegetation management program consisting of selective mowing and herbicide use for roadside right of way management. The Oklahoma State University roadside vegetation management program annually surveys ODOT field divisions concerning their weed management programs utilized in the safety zone immediately adjacent to the Interstate and state highway system in Oklahoma. The survey gathers information pertaining to the identity of major targeted weeds, acreage treated, herbicides utilized, and dates of application as well as applicator opinions on meeting vegetation management goals. Total ODOT managed acres treated for weeds during the period 2002 to 2011 averaged 92,955 acres per year, ranging from a low of 53,074 acres in 2006 to a high of 122,217 acres in 2007. In 2007 total acres treated for weeds increased by 31.5% over the 10 year average. This was due in part to higher rainfall that lead to increased weed pressure as well as an effort to increase the visual appeal of rights of way during the 2007 Oklahoma Statehood Centennial year. Widespread drought during 2006 and 2011 lead to a reduction of 43% and 5.5% respectively from the long term mean in total acres treated for weeds. In 2011 only 87,806 acres were treated for weeds by ODOT, representing a 20.4% reduction from 2010 acreage treated (110,360 acres). In 2011 69% of ODOT maintenance superintendents utilized weekends and evenings to complete herbicide applications. Use of non-traditional work hours increases the ability to utilize periods of lower wind speeds, reduced traffic loads, increased motorist visibility of herbicide application trucks bearing strobe lights at night and increased visibility of spray patterns illuminated with spot lights at night. Survey results are useful in tracking trends in the surveyed parameters and in formulating future research and education programs for ODOT.