Jayesh B. Samtani, Assistant Professor and Small Fruit Production Specialist, and Danyang Liu, Ph.D. Candidate, Hampton Roads Agricultural Research and Extension Center, Virginia Tech.

We are just about done with our strawberry season for 2019-20 growing season and like me, most of you are already beginning to think about the next strawberry crop cycle. Those growers who are looking for alternative strategies to custom fumigation treatments, may benefit from reading this article on anaerobic soil disinfestation (ASD).

Anaerobic soil disinfestation (ASD) was independently developed in Japan and in the Netherlands as alternatives to chemical soil disinfestation. The method involves using a large number of decomposable organic materials (or carbon source), applying irrigation to field capacity, and use of an impermeable mulch film to limit gas and create anaerobic conditions. Under anaerobic conditions, the carbon source is also decomposed by other microorganisms, which produce organic acids, aldehydes, alcohols, ammonia, metal ions, and volatile organic compounds that are suppressive or toxic to several soil-borne pests and diseases. Although ASD has been evaluated for strawberry in some geographic sites in the U.S there are no recommendations source types and rates, application protocol, and treatment duration for strawberry growers in Virginia and the mid-Atlantic region.

To this effort, we began ASD work in April 2017 by compiling a list of carbon (C) sources we could evaluate for ASD in the mid-Atlantic region. These C sources included sorghum-sundangrass residue, cowpea residue, buckwheat residue, brewer`s spent grain, used coffee grounds, and peanut shell. These C sources were chosen as they could be locally available during the preplant period in month of August to initiate ASD in open-field conditions. Dry rice bran was also included as a positive control as it is commonly used C source by California growers and works well for ASD. The cover crops were planted in a separate field outside of the strawberry field on April 2017. Eight weeks following cover crop seeding, cover crop was harvested, dried and chopped to use as C source. Due to the large number of C sources that we wanted to evaluate, ASD studies were initiated in greenhouse container environment. ASD was carried out for 3-week period and weed seeds were inoculated in containers. A non-treated control was used to compare the ASD treatments. As far as C sources are concerned, we found were no significant differences among C sources for the control of common annual weeds, chickweed and redroot pigweed, as well as yellow nutsedge which indicated that for further trials and applications, the consideration of C sources could focus primarily on local availability and cost. Weed viability was reduced 50 to 100% over non-treated control. These findings are published recently in International J. of Fruit Science. https://doi.org/10.1080/15538362.2020.1774472

Studies on ASD in open-field have been ongoing since fall 2018 at the Hampton Roads AREC, Virginia Beach and we are using brewers’ spent grain as our carbon source. We were able to procure the spent grain from a local brewery and we found it easier to transport those to our site than starting our own cover crops, especially for use as C source in ASD. Our second season field trial will be coming to an end as I write this week. ASD in our trial was done for a 3-week period. We are looking forward to analyzing data and comparing the ASD treated plots with non-treated and fumigated control. Particularly, we are looking at weed control ability and impact on crop yield with ASD in strawberry production. We hope to present some of these findings at the preplant strawberry meeting in July.

For growers who would like to experiment with ASD at their field site, the following publications will be useful to read through.

  1. Implementation of ASD in Florida tomato production https://edis.ifas.ufl.edu/pdffiles/HS/HS134500.pdf
    This publication walks the readers through the steps involved in ASD and how to calculate C and irrigation applications for a given area.
  2. Carbon to nitrogen ratios in cropping systems
    The above publication is useful for growers to remember ideal C:N ratio to allow for proper decomposition of C source and to support soil microbes that are critical for ASD.
  3. To get an idea of the C:N ratio of compostable materials and size of the C source material to put in the field.
  4. To get a hint of the how much water you need during ASD
    This article introduces “feel and appearance” method. It gives you a way to monitor soil moisture and to determine how much water to apply. The Soil Moisture Deficit (SMD) is how much water your need to bring to field capacity for ASD.

We recommend a treatment period of ASD for 3 to 4 weeks in open-field conditions. Paying attention to the C:N ratio in the soil is important too to allow for proper treatment. After the ASD treatment is done, you will have to punch holes in the strawberry bed ahead of transplanting time. At the time of punching holes, you will notice a pungent odor from the beds which is indicative that anaerobicity in the soil is achieved. The strawberries can be transplanted 10 to 14 days after punching holes. Planting earlier than 10 to 14-day period could result in plant toxicity. It is wise to try ASD on small-scale the first season to get familiar with the process and evaluate its effectiveness in controlling soil borne pests at your site. Be sure to compare this to non-treated or fumigated row beds.

Virginia Tech. Small Fruit Horticulture Program is now on Social Media Virginia Tech. Small Fruit Horticulture Program at the Hampton Roads AREC is now on Facebook and Twitter. The program’s username is @VTBerryBITES which comes with intent to share and update followers on Business, Innovation, Technology, Environment and Science news as it pertains to berry production including strawberry production. Once you ‘like’ the page on Facebook, or ‘follow’ on Twitter, you will automatically get updates of contents.

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