This project was to develop a committed roadside Johnson grass research area with controlled mowing and date of spraying adjacent to US 63 from I 74 south to JCT US 36 and to continue studies of a cold-adapted Johnson grass ecotype identified in the Northern-most tier counties in Indiana in an area adjacent to IN 23 between South Bend and New Liberty, IN. The cold-adapted Johnson grass provides a further threat of encroachment of roadside-established Johnson grass onto adjacent cropland of considerable potential economic consequence.

Completed was a 3-year study with Roundup alone and in combination with Outrider either as a tank mix or sequentially with Roundup followed after several weeks by Outrider or Outrider followed after several weeks by Roundup comparing different rates, dates of application and stages of development. Roundup alone or in sequence several weeks following Outrider was without effect on Johnson grass regrowth. A small benefit from 0.4 lb/A Roundup 3 to 6 weeks post Outrider was insufficient to justify the additional cost and offered no benefit over post Outrider mowing at the same stage. Correlations were with stage of growth with Johnson grass 24 to 30” tall, 33-36” tall and 40-42” tall without seed heads, seed heads forming in the boot, early anthesis (flowering), late flowering or with seed heads formed and 50-60” tall and spray date.

Fall 2006 marked initiation of the final implementation of the project. Outrider alone at a rate of 0.5 oz/100 gal plus a detergent at 0.12% of the total spray mixture spot sprayed to the point of runoff is to be recommended. Best results are expected with regrowth following mowing although about >90% control can be expected from midseason to late spraying of mature Johnson grass. Evaluated in 2007 and 2008 was the optimum regrowth stage to treat and the response to mowing following spraying. Johnson grass can be mowed very soon after spraying (next day or late same day) without loss of treatment effectiveness.

In laboratory studies, a candidate Outrider binding protein was identified and cloned.

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Johnsongrass, Chemical Control, Outrider, Growth Stage, Cold-Adapted Ecotype, SPR-2981

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Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, Indiana

Date of this Version