Efficacy of Turf Organic Herbicides
Horticulture & Turfgrass
Kelly Nichols
Ag Agent
University of Maryland Extension
Derwood
Abstract
In 2019, a law went into effect in Montgomery County in central Maryland prohibiting the use of synthetic pesticides on home lawns. In order to provide additional information to the lawn care industry in the county, organic herbicide efficacy trials were conducted in fall 2022 and summer 2023. In 2022, chelated iron, ammoniated soap of fatty acids, and caprylic acid + capric acid were included. While fall is not an ideal application timing for contact herbicides, chelated iron (regardless of rate) provided statistically similar control to the standard treatment of 2,4-D + dicamba + MCPP + carfentrazone, suggesting that chelated iron may have a role in an organic weed control program for lawns. The summer 2023 trials focused on corn gluten for pre-emergence large crabgrass (Digitaria sanguinalis [L.] Scop) control and chelated iron for post-emergence broadleaf weed control. Unfortunately, a cooler spring resulted in delayed crabgrass growth; data collected in July showed variable amounts of crabgrass across plots. Three rates of chelated iron (12.5, 25, and 50 fl oz/1000 sq ft) at three application intervals (3, 4, and 6 weeks) were applied. White clover (Trifolium repens L.) was the predominant weed across all plots. At the end of the study, treatments provided varying levels of percent clover reduction. Research will be continued in 2024.
Authors: Kelly Nichols
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Kelly Nichols Ag Agent, University of Maryland Extension, Maryland, 20855