Placement of metam potassium in combination with dimethyl disulfide, chloropicrin, and 1,3-dichloropropene for Cyperus rotundus L. and broadleaf weed control in tomato (Solanum lycopersicum L.)

Registered fumigants tend to provide poor or inconsistent Cyperus rotundus L. and broadleaf weed control. Dimethyl disulfide (DMDS) is generally considered more effective on Cyperus species than chloropicrin (Pic) or 1,3-dichloropropene (1,3-D) whereas metam potassium is generally considered more effective on broadleaf weeds. The objective of the experiment was to determine if the use of metam potassium in conjunction with other fumigants would enhance C. rotundus and broadleaf weed control in tomato. 1,3-D + Pic caused low level crop damage in spring 2014, increased crop height in fall 2014, and had no effect on crop growth in spring 2015. In every case, differences in crop damage or height did not result in yield differences. The most effective C. rotundus control was achieved with 131 kg ha−1 1,3-D + 200 kg ha−1 Pic, 340 kg ha−1 of DMDS + 90 kg ha−1 Pic, or 392 kg ha−1 of DMDS + 195 kg ha−1 metam potassium. Metam potassium improved C. rotundus control when applied alone or in conjunction with DMDS but not when applied in conjunction with DMDS + Pic or 1,3-D + Pic. All fumigants evaluated reduced broadleaf weed density compared with non-fumigated treatments. No consistent differences in total revenues or net benefit were observed among fumigants when applied without metam potassium. The use of metam potassium increased costs per hectare although DMDS + metam potassium was cheaper then 1,3-D + Pic but not DMDS + Pic. DMDS + Pic had the lowest estimated total cost of the three best C. rotundus treatments.