Utility of Anaerobic Soil Disinfestation and Organic Herbicides for Weed and Disease Management in Organic Solanaceous Vegetable Systems

View the project final report

Commodities

• Vegetables: peppers, tomatoes

Practices

• Pest Management: integrated pest management

A significant number of farmers are switching from conventional to organic production due to large consumer demands and high market cost of produce. Organic sales hit $55.1 billion in 2019 as the importance of organic continues to rise. Organic vegetable and fruit sales increase by 5 percent, hitting $18 billion, as the category continues to be the star of the organic sector, and often the starting point for organic food buying.

Weeds and pathogens, however, are challengers in sustainable production, specifically in organic vegetable production. Most of the organic growers rely on hand weeding, which can be labor intensive and costly. Weed density and biomass were found to be four times higher in the organic systems than in the conventional systems and under standard weed management practices, organic had 40 percent lower yield than the conventional system (Benaragama et al., 2016). Certain varieties of vegetables have been bred for resistance to key pathogens and insects, yet no type of inherent resistance mechanisms exists in crops that will directly resist weed infestation. Additionally, no selective herbicides are registered for use in organic vegetable production. There is a great need to develop alternatives for sustainable vegetable management.

Anaerobic soil disinfestation, a pre-plant biological soil treatment, has been shown to suppress certain weed species and soil-borne pathogens. Furthermore, preliminary data taken from the USDA-ARS United States Vegetable Laboratory in Charleston, S.C., by Dr. Cutulle and Dr. Wechter indicate that carbon source influences weed suppression. First developed in Japan and the Netherlands (Blok et al., 2000), ASD works by driving the soil into an anaerobic state for several weeks, thus reducing or eliminating the aerobic microorganisms. Most plant pathogenic microorganisms are aerobic. ASD is facilitated by amending the soil with a high carbon source, followed by sealing the soil in an impermeable plastic mulch and driving the soil into an anaerobic state by saturating the soil under the mulch with water. We propose evaluating several carbon sources that have allelopathic properties, and incorporate them into an ASD program. Additionally, a new liquid formulation of corn gluten meal has been developed in the past year. Proteins in corn gluten meal inhibit the germination of grasses and small seeded broadleaf weeds. We will test this product as both an ASD carbon source, as well as its effect on weed suppression. ASD has been shown to be an effective method for reducing or eliminating several soilborne phytopathogens. Dr. Wechter is currently working on the remediation of the devastating soil pathogen Ralstonia solanacearum that causes bacterial wilt of tomato and pepper. This pathogen is the most crop limiting pathogen of tomato in southern U.S. Preliminary work by Dr. Wechter has indicated that ASD is capable of greatly reducing and even eliminating the R. solanacearum in the field. Also, we will evaluate summer cover crops as carbon sources as an ASD scenario. This technique has also shown the potential to control nutsedge (Butler et al., 2012), but there is no study conducted in detail optimizing ASD as a multiple weed control technique.

• To determine the best allelopathic-organic herbicide amendment for control of annual grasses, broadleaf weeds, and sedge control in an ASD environment. Specifically the allelopathic material treatments will include mustard meal, sweet potato skins, dry corn gluten meal, liquid corn gluten meal, and no amendment.
• To determine if specific carbon source and allelopathic treatment combinations affect weed suppression and disease incidence in native coastal soil in the greenhouse. Specifically we will evaluate two carbon sources: Rice Bran and chicken manure plus molasses, with the best allelopathic amendments from Objective 1 in an ASD promoted environment.
• To evaluate the best options from the greenhouse trials and evaluate them in a field trial in the fall of year 1 and year 2 in pepper, tomato and eggplant.
• To determine the best summer cover crop residue for use as a carbon source in an ASD scenario in the field. Three cover crops will be evaluated: soybean, sunn hemp, and sorghum sudan grass.
• To determine if the best options compare to standard practices in commercial tomato and pepper farm settings in coastal South Carolina.