Johnsongrass Control in Corn with Eradicane Plus Accent or Beacon, 1996.

The population of rhizome johnsongrass was relatively low on June 21 in plots where Accent or Beacon had been used from 1992-1994. However, over the course of the season, considerable emergence of seedling johnsongrass occurred resulting in poor control by Oct. 1. Most likely these plants developed rhizomes and will result in a dense stand of rhizomatous plants within two years of not using Accent or Beacon.

I. INTRODUCTION:

A study was initiated in 1992 to evaluate johnsongrass control in corn with Accent and Beacon without or with Eradicane at 4.8 and 7.2 pt/A applied preplant incorporated. Following three annual applications of these herbicides rhizome johnsongrass had been eradicated as indicated by visual ratings and excavation of sample areas to find rhizomes (1992-1994). Consequently, it was decided to continue this study for several years to determine if Eradicane (+ Atrazine) would control seedling johnsongrass adequately without the use of Accent or Beacon to prevent development of rhizome plants.

II. Herbicides Evaluated:

      Aatrex 90 WG
      Eradicane 6.7 EC

III. ABBREVIATIONS USED:

      BROSOI: broadcast soil
      FC2X+CM: field cultivate 2 times + cultimulch
      SORHA: johnsongrass
      ZEAMX: corn

IV. RESULTS AND DISCUSSION:

Rhizome johnsongrass control only was rated on June 21 and rhizome and seedling control was rated on July 19 and Oct. 1. Aatrex alone controlled rhizome johnsongrass 0 to 13% on June 21 with no control of either type on July 19 or Sept. 30. In contrast, Eradicane plus Aatrex controlled rhizome johnsongrass 60 to 79% on June 21. This compares to 93 ot 97% control in the same plots at a comparable rating date in 1995. This indicates that some of the seedling population in 1995 became rhizomatous and produced rhizome plants in 1996. On July 19, control of seedling plus rhizome plants ranged from 46 to 81%, relatively similar to that observed on June 21. Considerable johnsongrass emerged in most plots between July 19 and Oct. 1, reducing the control in plots that had been relatively free of johnsongrass on July 19. Most likely, these johnsongrass plants developed rhizomes, which will produce rhizomatous plants in 1997. Based on these observations, it is likely that within two years following plots totally free of rhizomes, essentially a dense stand of rhizome johnsongrass will have reinfested these plots.

Corn Injury and Yield: There was no corn injury observed during the season. Because of very low rainfall during the growing season and competition from johnsongrass, corn ear development was very poor, thus yield was not taken in 1996. 

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