Integrated Systems of Weed Management in Organic Transplanted Vidalia® Sweet Onion Production

Abstract

<jats:p>Field experiments were conducted from 2008 through 2010 near Lyons, GA, to develop integrated weed management systems for organic Vidalia<jats:sup>®</jats:sup> sweet onion (<jats:italic>Allium cepa</jats:italic>) production. Treatments were a factorial arrangement of summer solarization, cultivation with a tine weeder, and a clove oil herbicide. Plots were solarized with clear plastic mulch during the summer fallow period before transplanting onion. Cultivation treatments were twice at 2-week intervals, four times at 2-week intervals, and a noncultivated control. Herbicide treatments were clove oil plus vinegar, clove oil plus an emulsified petroleum oil (EPO) insecticide used as an adjuvant, and a nontreated control. ‘Savannah Sweet’ onions were transplanted in early-December each year, with cultivation and herbicide applications events occurring the following January and February. Onions were harvested the following spring. In addition to yield measurement, a subsample of harvested onion was stored in a controlled atmospheric (CA) storage facility to evaluate treatment effects on diseases of stored onion. Summer fallow solarization did not control the cool-season weeds present in these trials. Cultivating transplanted onion with a tine weeder effectively managed cutleaf eveningprimrose (<jats:italic>Oenothera laciniata</jats:italic>) and swinecress (<jats:italic>Coronopus didymus</jats:italic>) and improved onion yields in 2 of 3 years. There was little difference in overall performance between two cultivations and four cultivations with the tine weeder. The 1 year of marginal weed control with the tine weeder was due to persistently wet soils during winter months that inhibited optimum performance of the implement. Clove oil, combined with vinegar or an EPO insecticide, provided marginal weed control and had no effect on onion yield. Diseases of stored onion were unaffected by any of the treatment combinations, although overall incidence of diseases of stored onion was higher in 2010 compared with other years. This corresponds with the 1 year of marginal weed control with the tine weeder, suggesting that the presence of weeds may be a factor related to disease incidence during storage.</jats:p>

Advances and Trends in Organic Fruit and Vegetable Farming Research

“…Soil solarisation, however, may not reduce the cool-season weeds due to the seed dormancy during the solarization treatment, as observed for organic onion (Johnson et al 2012). For wild blueberry, weed management can be achieved in part by soil pH management, although this technique is not effective for perennial woody weed species (Drummond et al 2012).…”

“…Similarly, mustard seed meal showed potential as a weed-suppressive amendment in organic production systems, although the risk of crop injury may be considerable, as was observed for onion (Boydston et al 2011). Vinegar and clove oil used alone or in combination are approved compounds that can be efficient depending on the weed species and developmental stages, but may cause injury (Webber et al 2009;Johnson et al 2012).…”

Pelargonic Acid for Weed Control in Organic Vidalia® Sweet Onion Production

“…Herbicides derived from natural sources have been investigated for weed control in certified organic crop production with many reports focused on the evaluation of performance on warm-season weeds. These studies evaluated commercial products, rates, times of application, and combinations with mechanical weed control in many cropping systems and regions Brainard et al, 2013;Curran et al, 2004;Johnson et al, 2012). Common conclusions drawn from these studies were that none of the essential oil herbicides provided any residual weed control, small weed size was critical for maximum efficacy, monocots were not controlled, environmental conditions affected herbicide performance, and rates necessary for maximum efficacy made the treatment costly.…”

“…Any strategy that reduces or eliminates the need for handweeding will provide a significant savings directly to growers. Previous research focused on an integrated system of summer solarization, cultivation with a tine weeder, and clove oil (Johnson et al, 2012), with the stated objective to lessen the need for handweeding. Of the weed control tactics studied, cultivation with a tine weeder was the most consistent and effective approach.…”

“…There is a need for an early season herbicide option in organic Vidalia Ò sweet onion to control emerged coolseason weeds before onset of cultivation with a tine weeder. Clove oil was proposed for this use, but inconsistency in controlling cool-season weeds during winter months negated that possibility (Johnson and Davis, 2014;Johnson et al, 2012). Pelargonic acid might provide a specialized niche in organic Vidalia Ò sweet onion production if control of emerged early season weeds is better and more consistent than clove oil or other herbicides derived from natural products.…”