Cutting Chemical Fumigation

Researchers studying natural method to help strawberry growers

By Doug Ohlemeier, Assistant Editor of Fruit Growers News

In strawberry farming, soilborne pathogens have long presented a challenge. Historically, chemical fumigation has been the preferred method of reducing harmful soil pathogens.

However, new regulations are making fumigation with synthetic chemicals difficult for small growers and farms close to public places. Anaerobic soil disinfestation can be used as an alternative to chemical disinfestation. The technology can be used in organic and natural growing by small farms that do not possess the technical capacity to fumigate as well as in farmland buffer areas.

Strawberry growers wanting sustainable alternative disease management measures could benefit from research being conducted by Virginia Tech (VA Tech) researchers. Scientists at Virginia Tech’s Hampton Roads Agricultural Research and Extension Center (AREC), are examining anaerobic soil disinfestation (ASD), a method that they say could revolutionize strawberry farming through finding sustainable approaches to disease control.

ASD works by depleting oxygen levels in the soil during the treatment period, producing toxic byproducts that kill soilborne pathogens. The majority of the disease-causing organisms are aerobic or need oxygen to survive and multiply. ASD and fumigation both seek to clean soil of pathogens and control soilborne diseases. In addition to pathogens, ASD also controls weed seeds, insects and nematodes.

Doctoral student Baker Aljawasim is part of Virginia Tech research examining how ASD can fight strawberry soil pathogens

Urgenecy Needed

“There is an urgent need for the adoption of sustainable alternative disease management measures that pose little threat to human health and the ecological system,” said Jayesh Samtani, associate professor for Virginia Tech and small fruit Extension specialist at the Virginia Beach, Virginia, AREC. “ASD with beneficial microbes could be an ecofriendly approach to controlling diseases and improving soil, especially in limited sources, organic farming, and smallholder farming. In addition, the use of ASD with beneficial bacteria in agriculture can greatly benefit integrated pest management (IPM) programs, particularly in situations where soilborne pathogens are a major concern.”

In a study conducted over two growing seasons, researchers in both seasons did not observe any natural incidences of crown rot or root rot on strawberry plants that emerged from soilborne pathogens. Interestingly, they viewed a reduction in fruit rot diseases: anthracnose fruit rot (causal organism Colletotrichum acutatum species complex) and botrytis fruit rot (Botrytis cinerea) in ASD treated plants.

Those rots are commonly observed every year in East Coast strawberry production. Though ASD treated plants produced lower yields than fumigated plots, Samtani said researchers noticed an increase in fruit sweetness and fruit pH over fumigated plants.

The ASD process is achieved by adding carbon sources and water under polyethylene mulch to create anaerobic soil conditions which stimulate buildup of anaerobic microbial populations. The technique causes changes in soil physical and chemical characteristics, such as the formation of volatile fatty acids, a decrease in soil pH, a rise in soil moisture, and changes in soil nutrients as a result of organic matter addition.

Anaerobic soil disinfestation quote from Dr. Jayesh Samtani

Another mechanism of ASD against soilborne pathogens is lowering the redox or chemical reaction potential below the critical redox potential, which can reduce the survival stage of soilborne pathogens, Samtani said.

“Engaging beneficial microorganisms such as endophytic bacteria that are used as biofertilizers or biostimulants with the ASD technique could generate a powerful tool to control soilborne pathogens,” Samtani said. “If we can optimize the technique to improve growth and yield of strawberries, it could play a role in sustainable crop production.”

Beneficial microorganisms can improve plant nutrition, support plant development under natural or stressed conditions, and increase the yield and quality of many important crops. In the interaction between beneficial microorganisms and plants, these organisms act as nutrient suppliers, phytohormone producers, plant growth enhancers, biocontrol agents of phytopathogens, and improvers of soil structure, Samtani said.

Additionally, climate change presents various obstacles including rising pest and disease threats, making it essential to implement techniques that boost plant resistance.

“Beneficial bacteria play a key role in strengthening plant immunity and adaptability, ultimately increasing the ability of strawberries to withstand environmental stressors,” Samtani said.

Samtani’s efforts focus on biofumigation for soil disinfestation, cultivar evaluation, extending harvest season, and supplementary nutrient application. The mission of his research and Extension program is to yield sustainable and economically viable solutions for berry production, and to recommend practices that improve agritourism experiences for growers and consumers.

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