Optimal rate of metam potassium for fusarium and purple nutsedge control when applied through the drip tape or with a minicoulter

Abstract

Metam potassium (metam-K) is a commonly used pre-plant fumigant in Florida plasticulture production. Two field studies on the dose-response of metam-K were conducted at the Gulf Coast Research and Education Center, Wimauma, FL, using two different application techniques for the control of purple nutsedge. In the first field study, multiple metam-K rates of 0, 130, 195, 260, 325, 390, 455, 520 kg ha−1 were applied with a minicoulter and were compared to the few commonly used herbicides such as 0.2 kg ha−1 sulfentrazone, 1 kg ha−1 s-metolachlor, 0.4 kg ha−1 fomesafen and 0.6 kg ha−1 oxyflurofen sprayed on the bed top. Percent purple nutsedge control was measured in all plots. The second field study evaluated five different metam-K rates (130, 260, 390, 520, 650 kg ha−1) in four different water volumes (54, 108, 162, and 216 m3 ha−1) when applied through drip irrigation within the bed. Herbicides reduced purple nutsedge density by 8–92% 6 weeks after fumigation compared to the nontreated control. Metam-K rates >455 kg ha−1 were needed to maximize purple nutsedge control. Water volumes had no significant effect on purple nutsedge and Fusarium oxysporum fsp lycopersici (FOL) control when metam-K was drip injected. Metam-K rates required to achieve 90% control of purple nutsedge at 9 weeks after fumigation were 612 and 766 kg ha−1 respectively in fall and spring 2018. All rates of metam-K were effective against FOL inoculum placed at bed center and 16 cm away from bed center, however, they were less effective on FOL inoculum placed at bed edges. EC90 values for FOL at the bed edges were 500 kg ha−1 in spring 2018. Optimal metam-K rates for purple nutsedge control were 10–30% higher than label rates when using an minicoulter and 57–96% higher than label rates when drip applied.