Planting Strategy Influences Vegetable Response to Glyphosate and Glufosinate Applied Preplant in Plasticulture

Abstract

In Georgia plasticulture vegetable production, a single installation of plastic mulch is utilized for up to five cropping cycles over an 18-month period. Preplant applications of glyphosate and glufosinate ensure fields are weed-free before transplanting, but recent data suggest residual activity of these herbicides may pose a risk to transplanted vegetables. Glyphosate and glufosinate were applied preplant in combination with three different planting configurations, including 1) a new plant hole into new mulch, 2) a pre-existing plant hole, 3) or a new plant hole spaced 15 cm from a pre-existing plant hole (adjacent). Following herbicide application, overhead irrigation was utilized to remove residues from the mulch before punching transplanting holes for tomato, cucumber, or squash. Visible injury, widths, biomass, yield of tomato, cucumber, or squash were not influenced by herbicide in the new mulch or adjacent planting configurations. When glyphosate was applied at 5.0 kg ae ha^-1 and the new crop was planted into pre-existing holes, tomato was injured 45%, with reduced heights, biomass, and yields; at 2.5 kg ae ha^-1 injury of 8% and a biomass reduction was observed. Cucumber and squash were injured 23% to 32% by glyphosate at 5.0 kg ae ha^-1, with reductions in growth and early-season yield; lower rates did not influence crop growth or production when the crop was placed into a pre-existing plant hole. Glufosinate at the same rates did not affect tomato growth or yield when planted into pre-existing plant holes. Cucumber, when planted into pre-existing plant holes, was injured 43 to 75% from glufosinate, with reductions in height and biomass, and yield losses at 1.3 and 2.6 kg ai ha^-1; similar results from glufosinate were observed in squash. In multi-crop plasticulture production, growers should ensure vegetable transplants are placed a minimum of 15 cm away from soil exposed to these herbicides.