Steam application with paraquat to control goat weed (Scoparia dulcis) in citrus orchards

Abstract

Reducing herbicide use in horticultural crop production can ameliorate adverse environmental effects but may also impact weed control effectiveness, especially as it pertains to difficult-to-control weeds. This challenge can be addressed by integrating a non-chemical strategy such as steam application with herbicide application. In this study, steam, as a non-chemical approach, was combined with post-emergence herbicide (paraquat) application for goatweed (Scoparia dulcis) management in citrus orchards. Two field trials based on randomized complete block design were conducted in citrus orchards in Immokalee, FL, in 2018 and 2021. Steam was applied to goatweed at a flow rate of 53 L ha−1 for 5–6 s. Twenty-four hours after steam application, low and high paraquat rates (0.3366 and 1.010 kg ai ha−1) were applied. In addition, the same rates of paraquat were applied without steam for comparison. Untreated checks (UTC) of no herbicide or steam applications were also included in the experiment as a control. Based on visual injury ratings, a combination of steam + low dosage of paraquat was as effective as the high dosage of paraquat alone and steam + high dosage of paraquat at 1, 8, and 16 days after treatment application (DAT) in 2018 trial and 1, 8, 16 and 22 DAT in 2021 trial.However, based on one site-year of biomass data, the percentage of dead weed biomass out of total biomass was statistically similar among all the treatments. Results from this study demonstrate that combining a low rate of paraquat applied in tandem with the steam application has the potential to provide effective goatweed control in citrus orchards.