Interaction of metam soil fumigant with the herbicides EPTC, pebulate, and rimsulfuron for yellow nutsedge (Cyperus esculentus) control in plasticulture tomato production

Due to the pending phase out of methyl bromide by 2005, alternative treatments for yellow nutsedge control are needed. In 1998 and 1999 field studies were conducted to evaluate EPTC (Eptam), pebulate (Tillam), and rimsulfuron (Matrix) alone and with metam soil fumigant for yellow nutsedge control and tomato tolerance in a plasticulture system.

In the plasticulture system pebulate and EPTC + metam resulted in the highest amount of visual injury, whereas rimsulfuron alone and with metam injured tomato plants less. These data correlate to the yield data, where rimsulfuron alone and with metam had the highest yields in both years. Pebulate alone and EPTC + metam had the lowest yields in both years. With respect to yellow nutsedge control, metam did not improve control over EPTC alone or pebulate alone. All treatments with the addition of metam had 100% yellow nutsedge control. To understand and support the field data a laboratory study was conducted to determine the dissipation rates of the herbicides in combination with a soil fumigant and under a plastic mulch.

Dissipation of EPTC and pebulate on a Sequatchie loam soil under plastic mulch in the absence and presence of metam (110 kg ai/ha) was examined in field experiments in 1998 and 1999 at Knoxville, TN. In the absence of metam, EPTC half-life (DT₅₀) was 9.0 d, and when applied in conjunction with metam increased to 20 to 23 d. For pebulate in the absence of metam, the DT₅₀ varied from 6.1 to 9.8 d and increased to 22 to 23 d when applied in conjunction with metam. The increase in half-life with the addition of metam is thought to be due to metam causing a reduction in the soil microorganisms that degrade EPTC and pebulate.