Exploring Local Carbon Sources and Cover Crops Used for Anaerobic Soil Disinfestation for Management of Soilborne Pathogens of Tomatoes in NC, USA

Project Overview

Project Type: On-Farm Research
Funds awarded in 2023: $30,000.00
Projected End Date: 03/31/2025
Grant Recipient: NC State University
Region: Southern
State: North Carolina
Principal Investigator:
Dr. Frank Louws
NC State University

Information Products


  • Vegetables: tomatoes


  • Crop Production: cover crops

    Proposal abstract:

    As a solution to this problem, we proposed to use carbon sources such as cover crops that are already part of the production systems of tomato growers. In NC, tomato growers finish tomato production around October and cover the soil planting winter wheat, legumes, or mixtures (winter peas, brassicas, rye, etc.) as cover crops. Then they incorporate these carbon sources into the soil, at least 2 months before tomato planting season (early spring). We propose that these cover crops can be incorporated into the soil and farmers can lay the plastic sooner than they usually do, initiating the ASD process earlier and keeping the plastic sealed until planting. This will allow anaerobic conditions to develop during the following weeks, reducing plant pathogen populations. Once the ASD process is complete, farmers can make holes in the plastic and proceed with planting tomato seedlings. In the past, the incorporation of cover crops has been hindered by the fact that root systems cannot be well incorporated and they affect good bed formation. However, a “reverse tiller” can be used which has a more forceful incorporation capacity with the reverse rotation leaving a deeper and cleaner bed in fewer passes than forward-rotating tines. Based on preliminary work and outcomes of objective 1, we envision growers may need to harvest cover crop residue from adjacent farm areas to supplement over-wintered growth in treated fields, in order to achieve the amount of carbon needed for maximum efficacy. Then ASD will fit into the already established production system of tomato farmers making its adoption easier and at a minimum cost. In addition, ASD has incredible potential to complement other practices such as grafting.  Tomato rootstock such as  “Maxifort” or “Beaufort'' show increased tolerance to V. dahliae infections, as well as increasing fungal species richness (Poudel et al. 2019). Field results from our group indicate that combining vigorous rootstocks with V. dahliae-resistant scions results in the highest yields in infested fields (Ingram, 2020). Combining ASD with resistant/vigorous rootstocks and resistant high-yielding scions should result in higher yields and lower disease severity. Comparing ASD and grafting with non-fumigated and fumigated treatments will allow us to determine the optimal practices for controlling V. dahliae in tomato field systems. This project provides novelty through the availability/development of novel genetics in emerging hybrids or rootstocks integrated into ASD systems using local carbon sources to suppress soilborne pests.

    Project objectives from proposal:

    A minimum of two years of on-farm research experiments will be conducted to assess the efficacy of ASD using winter cover crops and local carbon sources, combined with grafting/host resistance compared to the grower standard and optimized fumigated treatments. We will conduct the trials in a VW-infested grower field (see letters of cooperation from growers and/or agents). We hypothesize the combination of ASD using winter cover crops and grafted plants will increase soil quality and reduce pathogen inoculum levels over time. In the on-farm work, the experimental design will be laid out as a randomized complete block design (RCBD) with a split-plot arrangement and 4 replications. The main plots will be soil treatment 1) an untreated control (UTC); 2) fumigation standard (Pichlor 60); 3) ASD1 using brewers spent grain and 4) ASD2 using winter wheat (Table1).


    Table1. Potential field design for On-farm research

           plots splots r Main_plot               subplots

        101      1      1 Fumigated    Non-grafted

        101      2      1 Fumigated     Grafted

        102      1      1      ASD2     Grafted

        102      2      1      ASD2      Non-grafted

        103      1      1   Control       Non-grafted

        103      2      1   Control       Grafted

        105      1      1      ASD1      Non-grafted

        105      2      1      ASD1     Grafted


    Each soil treatment plot will be three beds wide with a “Buffer Bed” in-between blocks. All data will be secured from the middle beds only. Each main plot is also separated by a buffer. Sub-plots will be transplanted to the grower standard tomato cultivar and up to two grafting treatments using rootstocks grafted to the grower standard scion. All grafted plants will be grafted by our team. Each unique treatment area will include a minimum of 10 plants to collect field data buffered by a minimum of 5 plants at each end of the treatment unit.


    In our discussions, the grower indicated they would like to do work on a larger scale also (see  Letter of Support - Leatherwood). To accommodate this extra gower goal, another trial will be conducted in which half of an acre will be managed according to grower standard practices and the other half of the acre will be produced by incorporating the winter cover crop using the reverse tiller, laying plastic, and saturating the field with water to induce anaerobic conditions until the planting day. We anticipate two treatments for this trial 1) Growers' standard practice and, 2) ASD using winter wheat as a cover crop. In addition, a parallel experiment will be conducted at a research station (Mountain Horticultural Crops Research and Extension Center, Mills River, NC) in a field with a history of high VW pressure. This will also be an RCBD experiment with main plots as above but include more subplots of grafted tomato. In the case of the research station work, the trial will be carried on to the third year. The first two years will secure data parallel to the on-farm work and will explore broader questions about the interactions of ASD, tomato genetics, microbial ecology, soil health, and tomato productivity. This research-station-based work will be funded primarily by other grants.


    Procedure for field preparation: Soil will be prepared (disced, pre-plant fertilizer, pH adjusted) in advance by the grower. In our experience, we work with the grower who manages all equipment and calibrations, etc. In cases where cover crops are not used, Beds are pre-formed, and the carbon sources are placed on top of the pre-formed beds and rototilled into the bed to ensure thorough mixing; then in one pass, the soil is pulled, drip tape laid down and the bed is covered with TIF; fumigant is turned on or off according to soil treatment. For cover-crop treatments, existing cover crops (and supplemental cover crops if needed) will be added to the soils and incorporated, and then beds are pulled as above. Subsequently, lay flat tubing is rolled out and ½ inch of the non-perforated hose is fed to each ASD bed to saturate the ASD beds by splicing into the buried drip tape and capping the ends of the ASD area. Drip tape is “reattached” using connectors so lines can subsequently be used to water the entire bed row within a treated area. In our experience, this procedure has worked well. Redox and temperature values will be captured in selected plots using the Indicator of Reduction in Soils (IRIS) tubes (Rabenhorst 2010). Beds will be prepared in the early spring 2 months before planting tomatoes for a late crop (target planting date ~ first week of June).


    Disease ratings will be conducted every week once the first symptoms appear during both year 1 and year 2, and disease ratings will be used to form an area under the disease progress curve (AUDPC) to optimally assess disease damage (Jeger and Viljanen-Rollinson 2001). Five harvests will be conducted, and fruit weight and size will be assessed. We will secure data from the inner 10 plants of the inner bed of each subplot; the grower will harvest all other fruit and can sell all fruit since all experimental inputs are registered/allowed. The grower will manage all day-to-day fertility, watering, training, and pest management.

    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.