ASHS 2024 Conference

Planting-hole Steam Application for Pathogen and Weed Control in Organic Strawberry in Southern California - Oleg Daugovish
Elucidating the Impact of Anaerobic Soil Disinfestation on Organic Watermelon Production in South Carolina - Sohaib Chattha
Alternative Carbon Sources for Anaerobic Soil Disinfestation in California Strawberry - Oleg Daugovish
Sweetpotato (Ipomoea batatas) Variety Tolerance to Different Herbicidal Weed Control Methods - Alyssa Miller
Soil Steaming: A Sustainable Weed Management Strategy in Sweetpotato - Alaina Richardson
Assessment of Various Carbon Sources for Anaerobic Soil Disinfestation to Manage Weeds in Organic Sweetpotato - Simardeep Singh
Evaluation of saturated steam with boiling water to control Guinea grass (Megathyrus maximus) in riparian

Organic strawberry production has been expanding in California, but opportunities for crop rotation are limited due to lack of organically certified fields. Continuous strawberry production promotes soil-borne pathogens, such as Macrophomina phaseolina, the causal agent of charcoal rot and increases populations of weeds. These problems are exacerbated by lack of cost-effective management tools. In summer and fall production seasons at Oxnard, CA we evaluated pre-plant steam injection to raise soil temperature to 70 C or above for at least two minutes. Steam generated on-site was applied via four 25-cm long spikes to planting holes in raised beds covered with the plastic mulch. Five to ten days later, bare-root strawberry plants were placed in six steamed and six untreated plots and their performance and fruit production assessed. Additionally, we collected soil at 0-25 cm for analyses of resident Macrophomina phaseolina abundance before and after treatment and evaluated weed densities in planting holes. Steam application reduced M. phaseolina microsclerotia levels 80% in summer and 96% in fall. Steaming provided near 100% control of weeds germinated from the soil seed bank, but had no effect on germination of wind-dispersed weeds deposited to holes after steaming as was the case with fumigants. In summer season, strawberry mortality due to soil-borne pathogens was 12-18% in steamed plots and 70-75% in untreated soil. Due to loss of plants, marketable fruit yields in untreated plots were reduced 95% compared to steam treatment. No early-season plant mortality occurred in fall season but strawberry plants were 39 and 54% larger at two evaluation dates in steamed plots compared to untreated soil. We continue evaluations of fruit production and plant responses to soil pathogens. The completed work suggests that hole steaming may be very effective in suppressing soil-borne pathogens and weeds interfering with organic strawberry production in coastal California.

Anaerobic soil disinfestation (ASD) has been adopted in approximately1,000 ha in California strawberry production as an alternative to chemical fumigation of soil. Rice bran, the predominant carbon source for ASD, has become increasingly expensive. In 2022-2024 field studies at Santa Paula and Oxnard, CA we evaluated 20-30% lower-priced wheat middlings (Midds) at 6 or 7 t/acre as alternative carbon sources to rice bran. The ASD treatments were applied in August at each location in preparation for strawberry planting in October. Soil and air temperatures were 18-35 C during that time. After incorporation of carbon sources into the top 30 cm of bed soil, beds were shaped, irrigation drip lines installed and covered with totally impermeable film (TIF) to prevent gas exchange. Beds were irrigated to full capacity within 24 to 72 hours after TIF installation. Anaerobic conditions were measured with oxidation reduction potential (ORP) sensors placed at 15 cm depth. Midds plots maintained Eh at -180 to 0 mV during the two ASD weeks at Santa Paula and -300 to 0 mV during five weeks at Oxnard, while untreated soil was aerobic at 200 to 400 mV. At Santa Paula, permeable bags with inoculum of Macrophomina phaseolina, a key soil borne pathogen of strawberry, and tubers of Cyperus esculentus, the most difficult to control weed, were placed 15 cm deep in soil and retrieved two weeks after ASD initiation for analyses. At Oxnard, resident populations of M. phaseolina and C. esculentus in soil were assessed before and after ASD. Two weeks after the completion of ASD, holes were cut to aerate beds and bare-root strawberry were transplanted into them: ‘Fronteras’ at Santa Paula and ‘Gaviota’ at Oxnard. ASD with Midds reduced viable microsclerotia of M. phaseolina 75% at Santa Paula and 98% at Oxnard. ASD treatments reduced tuber germination of C. esculentus 68-74% compared to untreated soil. Additionally, Midds and DDG provided greater sufficiency of plant-available nitrogen and increased fruit yields 40%, compared to untreated soil at Santa Paula. We continue fruit production evaluations at Oxnard in 2024. ASD with wheat middlings as a carbon source can suppress soil pathogens and weeds and help sustain organic strawberry production in California.

There are limited herbicides labeled for use in sweetpotato (Ipomoea batatas) production in the United States. Therefore, the registration of additional herbicides with different modes of action (MOA) would provide growers added weed control options to enhanced crop yield and provide a more sustainable sweetpotato (SP) production system. As herbicide-resistant weed populations continue to emerge and become more prevalent, weed control strategies need to include herbicides with different MOAs for the long-term success of (SP) cultivation. This research will identify herbicides, along with rate and application time that could be registered for use in sweetpotato. Herbicide tolerance of four (SP) varieties (Beauregard, Orleans, Dianne, and Covington) were evaluated in a screening study. These varieties were selected to represent sweetpotato production areas across the United States in Arkansas, California, Louisiana, Mississippi, and North Carolina. Herbicides evaluated include fluridone, glyphosate, glufosinate, carfentrazone, saflufenacil, acifluorfen, and others. The study involved the foliar application of herbicide treatments at 1X and 0.5X rates, laid out in a completely randomized design, using a spray chamber onto individual (SP) plants cultivated in 4x4 inch containers within the controlled environment of the Dorman Hall Greenhouse at Mississippi State University. Visual assessments of herbicide-induced injury were conducted at regular intervals of 7, 14, 21, and 28 days after treatment (DAT), accompanied by measurements of vine length in centimeters. Furthermore, dry root and shoot biomass were quantified at 28 DAT to provide a comprehensive assessment of herbicide impacts on (SP) growth and development. Data was analyzed using ANOVA and means separated by Fisher’s protected LSD (α=0.05). Results indicate varying levels of tolerance among the (SP) varieties to specific herbicides and application rates. Noteworthy trends in visual injury, vine length, and biomass measurements highlight the nuanced responses of the cultivars to different herbicide chemistries.

The Sweetpotato (Ipomoea batatas (L.) Lam.) has flexible uses as food, feed, and industrial product usage. There are over 27,000 acres across one-hundred and fifty farms in Mississippi and the state also ranks second and third in the nation in acreage and production, respectively. It is paramount for all farmers to suppress weed species, enhance biodiversity, improve soil health, and minimize pests and diseases in plants. In sweet potatoes, there is a significant problem with weeds interfering with yields, reducing crop yield by up to 80%. A chemical approach is usually the most popular utilization, but it can lead to disadvantages with crop quality, intolerance, and, in worst-case scenarios, environmental toxicity. To overcome limited weed control options and preserve or improve sweet potato quality and yield for Mississippi growers, there is a great need to find a supplemental weed control strategy. One solution is the utilization of soil steaming, an alternative method that is environmentally friendly and organically favored. This study aimed to assess the most effective soil steaming depth and duration for controlling a troublesome weed in sweetpotatoes, yellow nutsedge (Cyperus esculentus (L.)). This study is conducted in split plot designs with the soil steaming plots as the main plots in field and greenhouse situations. This was to test different durations of times and depths in the soil for both areas. Depths of 2, 5, and 8 inches, were used. Times of 0, 1, 5, 20, 45 minutes, were used. Maximum temperatures reached were 82 ºC. The germination count was recorded at 21 DAT. The highest weed coverage (55%) was observed in 0 minutes duration. The second highest (30%) was observed at 5 minutes. The least amount of coverage (20%) was observed at 20 minutes. The adoption of soil steaming would be beneficial in sustainable suppression of yellow nutsedge in organic sweetpotato farms. Keywords: soil steaming, weed suppression, sweetpotato, sustainability, organic

Yellow nutsedge (Cyperus esculentus L.) management in organic plasticulture systems is challenging as it reproduces both by seeds and tubers. Yellow nutsedge has a strong midrib and sharp leaf tip which allows it to puncture plastic mulch and creates favorable conditions for other weeds to grow, compete for resources with crop plants, and decrease crop yield. Lack of available herbicide options in specialty crops make weed management more challenging. Anaerobic soil disinfestation (ASD) is a technique that has shown potential to manage weeds in organic production systems. ASD is facilitated by incorporating carbon sources into the soil, tarping the soil with plastic mulch, and irrigating to the soil saturation. A field study was conducted at Clemson University’s Coastal Research and Education Center, Charleston, South Carolina, to evaluate the impact of various carbon sources in ASD on weed management in organic sweetpotato. This treatment structure for this study consisted of a factorial with four carbon source treatments (cotton seed meal, chicken manure molasses, brassica waste, and non-amended control) and four sweetpotato cultivars (Bayyou Belle, Muraski, Monaco, and USDA 18-040). These sweetpotato cultivars have two different growth habits, either bunch type (USDA 18-040 and Monaco) or spreading type (Bayyou Belle and Muraski). The primary purpose of using different plant architecture is to evaluate the impact of the sweetpotato vine growth habit on weed emergence. Experimental plots receiving chicken manure molasses and cotton seed meal as carbon source resulted in the greatest cumulative anaerobic conditions (

Boiling water and steam have been effectively used as a non-chemical means to control weeds in croplands and urban areas. In Hawaii, it is a relatively new technology with limited trials done on local conditions and weeds. Guinea grass (Megathyrsus maximus) is a noxious weed that invades landscapes and agricultural fields in Hawaii and throughout the world. While it is typically controlled using herbicide sprays, this may be restricted if the guinea grass being controlled is located in riparian areas. In this study, we evaluated the efficacy of saturated steam with boiling water in controlling mature clumps of guinea grass growing along a streambank. Guinea grass bunches were divided into small (less than 15.2 cm) and large clumps (15.2 to 30.5 cm) and then cut 5 to 15 cm from the ground. Cut clumps were either not treated (control) or treated with saturated steam and boiling water for 1 minute using a 15cm long spike injector inserted into different points of the crown. Percent green color and number of resprouts were collected 7, 14, and 21 days after application. Dry biomass was collected 22 days after application. Results indicate that saturated steam with boiling water was effective in controlling guinea grass clumps. Small clumps were completely controlled (no resprouts and new biomass) while large clumps had significantly reduced the number of resprouts and reduced production of new biomass. Saturated steam with boiling water offers a non-chemical means to control guinea grass in riparian areas in Hawaii.