Biosolarization For Disease and Weed Control For Winter High Tunnels

Final report for FNC20-1223

Project Type: Farmer/Rancher
Funds awarded in 2020: $9,000.00
Projected End Date: 01/31/2022
Grant Recipient: Box Turtle Farm LLC
Region: North Central
State: Missouri
Project Coordinator:
Jason Hirtz
Box Turtle Farm LLC
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Project Information

Description of operation:

After becoming interested in sustainable agriculture, I interned at Ivan Stoilov’s Fig Farm in Dittmer, Missouri in 2007, where I took part in my first SARE funded project. Box Turtle Farm was established in 2008 operating as a CSA subscription service for two years. In 2011, my wife and I relocated to a 16-acre farm in Mount Vernon, Missouri to expand operations.

After this move, Box Turtle Farm dropped the CSA model and began focusing marketing efforts towards grocery stores and restaurants. In 2013, the farm obtained USDA organic certification to improve marketability. Since 2012, Box Turtle Farm has produced salad through winter. Our first efforts were in temporary caterpillar tunnels. In 2016, we expanded on that idea by growing bunching greens and cucumbers in the summer through a SARE funded project titled “Evaluation of Alternative Coverings for Year Long Utilization of Caterpillar Tunnels”. It was our first major step toward producing cool season crops through summer.

The farm still produces cucumbers, bunched greens and summer squash, but the main focus has become salad crops. Since the fall of 2017, we have produced salad crops on a weekly basis utilizing over 16,000 square feet of high tunnels. In my region, I have become one of the leaders in the high tunnel salad production niche. I have shared my knowledge by speaking on the subject at several conferences including the Great Plains Growers Conference, the Midwest Winter Production Conference, and Frozen Ground.

Summary:

Winter high tunnel salad production has become a viable income stream for many vegetable producers. The winter environment within an unheated tunnel is good for leafy greens, but it is also perfect for cool season weeds and soil borne pathogens. Most producers find these to be limiting factors in the success of their winter crops.

Biosolarization is a new method of disease and weed control. Organic matter is incorporated into the soil, and then the soil is irrigated and covered with clear totally impermeable film (TIF) plastic. TIF is designed for soil fumigation. The sun heats the soil beyond typical field conditions, and the hot, moist soil rapidly decomposes the organic amendments. The byproducts of decomposition are kept in the soil by the gaseous impermeable TIF plastic. These compounds, combined with the heat, negatively impact soil borne pathogens and weed seeds without the use of fungicides or herbicides.

I am seeking to test the efficacy of this technique, using farm generated grass clippings, in high tunnels in the summer to reduce winter disease and weed pressure. I would also like to test used greenhouse plastic as an affordable and sustainable TIF plastic alternative.

Project Objectives:

Biosolarization is still a relatively new technique. In California, it shows promise as a solution to weed and disease pressure in field grown salad crops. Our objectives are:

  • to test to see if its benefits will carry over from the summer season to winter crops in high tunnels in the Midwest;
  • to compare used greenhouse film as a sustainable and affordable alternative to TIF plastic;
  • and how the quantity of feedstock, farm generated grass clippings tilled into the soil, affects the outcome.

Research

Materials and methods:

The trial will be conducted in two high tunnels, high tunnel A and high tunnel B. Six beds will be formed in each tunnel. Grass clippings will be mowed with a riding lawn mower and collected with a towed yard vacuum. I have chosen grass clippings as the feedstock because I believe it is an underutilized, sustainable feedstock available to most small farmers. I have chosen to use a riding lawn mower and yard vacuum because I see these as scale appropriate, affordable and accessible to farmers with small to mid-sized high tunnel operations.

Beds will be labeled one through six in each tunnel. Each of the six beds will receive a different amount of grass clippings as follows; Bed 1 0#, Bed 2 50#, Bed 3 100#, Bed 4 150#, bed 5 200#, bed 6 0# (the control). For consistency, all of the grass clippings will be mowed and collected at the same time and tilled in immediately after collection. The varying amounts applied are to determine the quantity of grass clippings needed for best results. No resources are unlimited and we need to know the least amount that is effective. Beds will measure 66 feet long and 50 inches wide.

All beds will be irrigated. In both high tunnels, beds 1-5 will be covered in plastic. Bed 6 will be left uncovered as a control. Beds in high tunnel A will be covered in TIF plastic, and beds in high tunnel B in used greenhouse plastic. Beds will remain covered for 10 days.

 

Research results and discussion:

Progress to date:

We tweaked our materials and methods as follows: Grass clippings were collected and applied to beds on August 22, 2020. All Beds were tilled and covered on August 23. The beds were left covered for five extra days, for a total of 15 days because the weather was unseasonably cool and cloudy. All test plots were planted on September 12. A paperpot transplanter was used for planting the lettuce seedlings. The beds had to be tilled again before planting because there was enough residue left on the soil surface from the grass clippings to clog the transplanter. Monthly data collection was done from October through February.

Lettuce will be planted to each bed. If cultivation is needed, before and after pictures will be taken for comparison of weed pressure. Losses or damage from disease from each bed will be recorded for comparison.

Monthly data collection was done from October through February.

Wire worms damaged the control crops in one house. These high tunnels were new and I have had similar damage in all  of my other four high tunnels in their first year of cultivation. In the first weeks after planting, there were significant losses. Deceased lettuces were pulled and inspected and it was confirmed the damage was from wire worms. Approximately 2/3rds of the crop survived, but it didn't thrive. There was no similar damage on the beds treated with biosolarization.

Data was collected once a month from October through February. Those results will be compiled for the final report.

n August 2020, I began the biosolarization process in both of the trial high tunnels. Six beds were prepared in each tunnel. In each tunnel, one bed received 200# of grass clippings, one received 150#, one 100#, and one 50#. Two beds in each tunnel were left without grass clippings. Each bed was tilled and irrigated. In one tunnel five beds were covered in tif plastic; the other tunnel, recycled high tunnel plastic. As a control, one bed in each tunnel did not receive any grass clippings and was not covered in plastic. Because the weather was unusually rainy for August, the plastic was left in place for 12 days rather than the proposed 10 days. Once uncovered, each bed was planted to lettuce using a paperpot transplanter.

Immediately after planting, wireworm damage began to appear in both tunnels in the two beds that received no grass clippings; approximately 30% of those plants died. The remaining plants in those beds remained stunted throughout the winter. No wireworm damage was witnessed in the beds that received grass clippings. Evaluating biosolarization for wireworm control was not planned as part of this project. We have struggled with wireworm control in new plots as all of our vegetable plots have previously been in fescue pasture. I was surprised and excited to see this benefit.

There was no discernable difference in weed control between the control plots nor the plastic coverings. Once a month, a random sample of each of the 12 beds was selected, and weeds counted and recorded. After recording weed numbers, the beds were cultivated; this monthly cultivation was the only cultivation they received. We typically cultivated weekly during the fall months. Although a comparable weed count was not conducted, I believe, across all beds, weed pressure was much lower than in our other high tunnels. I speculate covering 5/6ths of each tunnel floor with clear plastic and closing both tunnels in August had some effect on the uncovered control beds. Exploring short term solarization for weed control could be the topic of another study.

Sclerotinia control from the plastic treated plots, whether they received grass clippings or not, was good. Sclerotinia was an issue in the uncovered control plots. Botrytis affected lettuce across all beds evenly. The botrytis was left untreated. I wanted to evaluate sclerotinia, and I didn’t want fungicide treatments to interfere.

Finally, I saw no real difference between the two types of plastic. The recycled high tunnel plastic performed as well as the TIF plastic.

Participation Summary
1 Farmers participating in research

Educational & Outreach Activities

10 Consultations
1 Curricula, factsheets or educational tools
2 Webinars / talks / presentations

Participation Summary:

75 Farmers participated
Education/outreach description:

April 29, 2020, I was a guest on the Thriving Farmer Podcast with Michael Kilpatrick. I spoke about my past experience with biosolarization and my SARE Grant. I have received numerous phone calls and emails about the topic and, by sharing my experiences, have helped guide those interested parties.

 

January 7,2022, I presented at the Great Plains Growers Conference in St. Joseph, MO. I prepared a Power Point presentation and spoke for 30 minutes to those attending in-person and virtually. I gave a copy of my Power Point to session's moderator for further use by SARE and I have added a copy to my media files here. A live recording of the presentation will be available soon and I will share that version via social media.

Learning Outcomes

10 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
Lessons Learned:

I will continue to use biosolarization in my production. It seems to have reduced wireworm populations and sclerotinia. I did have better lettuce production in the biosolarized plots. Solarization alone may achieve similar sclerotinia control; however, I see no drawbacks in adding the extra step of incorporating organic matter. Acquiring organic matter may be a limiting factor for some farmers. The smaller quantities of 50# of fresh grass clippings per 300 square feet worked as well as the larger quantities. I also found that recycled high tunnel plastic worked as well as the expensive, somewhat difficult to acquire TIF plastic. I would highly recommend farmers try this with their own materials. I didn’t see any obvious downsides or find the basic process difficult. Biosolarization is a relatively new field, and we need more experimentation and sharing of experiences.

Project Outcomes

Recommendations:

I would like to see short term solarization trialed for disease and weed control. A 30 day period of solarization is typically recommended. My trial suggests that, in some situations, as few as 10 sunny days may be beneficial. I would also like to see further study of the effects of biosolarization on wire worm populations. I saw severe wireworm damage on the untreated crops and no damage on the treated crops. I would like to see if that could be replicated as I've not seen reliable organic controls for that pest.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.