Phytotoxicity to transplanted lettuce (Lactuca sativa) of three pre-emergence herbicides: metolachlor, pendimethalin, and propachlor

Abstract

The phytotoxicity of the pre-emergence herbicides metolachlor, pendimethalin, and propachlor to heading lettuce was investigated in 5 experiments conducted in southern Queensland during 1990-91. Metolachlor was applied before transplanting lettuce seedlings in 2 experiments. On a krasnozem soil at Toowoomba, spraying >1.75 kg a.i./ha reduced lettuce growth and the number of marketable lettuce heads. When applied on a black earth at Gatton, 1.44 kg a.i./ha stunted the lettuce and reduced the number of marketable heads by 30% compared with hand-weeded treatments. On both soils, 2.2-2.9 kg a.i./ha of metolachlor is recommended for broadleaf weed control in other crops. The risks of phytotoxicity from such rates preclude its use in transplanted lettuce in this environment. Lettuce were severely stunted from application of 1 kg a.i./ha of pendimethalin after transplanting. Spraying at the same rate before transplanting initially reduced lettuce width in 1 of 4 experiments, but the lettuce recovered. Lettuce yields from areas treated with 1 kg a.i./ha before transplanting were unaffected. The number and size of harvested heads tended to decline where >1.3 kg a.i./ha was applied. Higher rates (up to 1.5 kg a.i./ha) may be acceptable on krasnozem soils. Use of pendimethalin at 1-1.3 kg a.i./ha would control or suppress many important broadleaf weeds in lettuce, as well as a range of grasses. Propachlor was less phytotoxic when applied immediately after transplanting the lettuce seedlings than when sprayed before transplanting. Yields were unaffected from application of 2-2.5 kg a.i./ha after transplanting on black earth and sandy soils. When sprayed before transplanting, >2 kg a.i./ha caused significant yield reductions in several experiments, although lettuce grown on a krasnozem soil appeared more tolerant. Use of 2 kg a.i./ha of propachlor would give a suppressive effect against several broadleaf weeds, but another herbicide would also be required to achieve effective weed control. A spraying strategy involving pendimethalin and propachlor herbicides in transplanted lettuce has the potential to reduce weed control costs by up to 80%.

Weed Management in Transplanted Lettuce with Pendimethalin andS-Metolachlor

“…Results here are in agreement with Henderson and Webber (1993), who observed high tolerance of transplanted lettuce to pendimethalin (PRE) applied at rates between 0.5 and 2.6 kg ha À1 . In contrast, these authors observed lettuce injury and yield reduction caused by metolachlor (PRE) at rates higher than 1.4 kg ha À1 , whereas in our study, Figure 1.…”

“…S-metolachlor at 2.8 kg ha À1 was safe for the transplanted lettuce plants (Figures 1 and 2). The original metolachlor formulation (blend of isomers) used in the Henderson and Webber (1993) study vs. the purified S-metolachlor formulation used in this study might be the explanation for the differences in rates causing spinach injury (O'Connell et al 1998). However, PRE applications of S-metolachlor at the label rates recommended for other vegetables (0.7 to 1.1 kg ha À1 ) did not cause significant injuries and yield reduction, which indicate a possible role for this herbicide in transplanted lettuce.…”

“…Tolerance of transplanted lettuce to herbicides is higher beyond that of seeded lettuce (Fennimore et al 2014;Gorski et al 1988). Henderson and Webber (1993) evaluated pendimethalin (0.5 to 2.6 kg ai ha À1 ) and metolachlor (1.4 to 5.8 kg ha À1 ) in transplanted lettuce. Those authors found pendimethalin and metolachlor to be safe for transplanted lettuce to some extent, but did not address weed control.…”

Bioremediation of pendimethalin-contaminated soil

“…It was found that, dinitroaniline herbicides kill seedling weeds by inhibiting the development of lateral roots in susceptible plants, stunting the above-ground parts, with the development of a dark green color, swelling and brittleness of the stem or seedling hypocotyl (Parka and Soper, 1977). Severe crop phytotoxicity and damage symptoms reported in literature range from reduced or inhibited germination, reduced root length, protein and nucleic acid contents of root tips, injured flowers, to complete crop failure and residual persistence of herbicides in crop and soil (Henderson and Webber, 1993;Sinah et al, 1996). Pendimethalin caused seedling mortality (Aluka, 1997), but does not prevent seedling emergence (Akobundu, 1987;Smith, 2004;Smith, 2006).…”

Evaluation of some pre and postemergence herbicides for weed control in yacon

“…The phytotoxicity of dimethanamid and acetochlor was low in sunflower when applied preplanting and lightly soil-incorporated (Popescu 1995). Metolachlor and propachlor applied before transplanting were damaging to lettuce, and pendimethalin severely stunted lettuce when applied after transplanting (Henderson & Webber 1993). In dandelion, pre-emergence trifluralin (also incorporated), aziprotryne, chloroxuron and methabenzthiazuron were well tolerated in a direct seeded crop, but pendimethalin reduced plant numbers (Mitchell & Abernethy 1994).…”