Could a Soil Fumigant be Used as a Bio-Stimulant?

Common knowledge or conventional wisdom is just that, something that is generally accepted as fact, until it isn’t. We can look throughout history and find plenty of things that were generally accepted until new discoveries challenged and disproved those things. For decades, the living, microscopic portion of our soils has been somewhat of a mystery. If the organism wouldn’t grow in a petri dish, it was difficult to know if it was present and if its’ populations were increasing or decreasing. Modern techniques have provided far greater insight into the microbial world that lives unseen in our soils. We can now extract genetic information from a teaspoon of soil and determine which organisms are present through their genetic fingerprints.

Now on to soil fumigation: the process of applying a liquid below the soil surface which subsequently transitions to the gas phase and the vapors move through the soil profile. These vapors are present from days to weeks based on the chemistry and application technique. Depending on the fumigant used, the vapors can be toxic to soil borne pathogens, nematodes, and weed seeds. This is why soil fumigants were originally put into use, to control soil borne diseases. Based on this information, it is easy to jump to the conclusion that soil fumigation would have devastating impacts on soil microbial communities. In fact, we often hear that soil fumigants sterilize the soil. Reducing populations of certain organisms such as Fusarium or Rhizoctonia are advantageous, but there are multitudes of organisms that are beneficial to plant growth and soil function, and it has been assumed that these have been equally reduced like the pathogens.

Enter modern techniques. A group of scientists at the University of Florida have been investigating the impact of soil fumigation on microbial communities and recently published some of their findings ( This group looked at soil microbial communities in a plasticulture tomato production system before and after fumigation with several different fumigant treatments as well as beds that were left untreated. First off, even the most effective soil fumigants don’t sterilize soils. There are a multitude of organisms that were found shortly after fumigation. They also found that fumigant treatments with greater than 60% chloropicrin consistently increased tomato yield, which is why producers use these products. The use of fumigants resulted in significant changes in the soil microbial communities and fumigants reduced the microbial diversity of soils, but these changes are temporary and those soils reverted to their original state by the next growing season. Some of these changes in microbial complexity could hinder some of the major functions of microbes in the soil such as nitrogen metabolism and carbon fixation. So, these findings do not come as a huge surprise to anyone who is familiar with soil fumigants and how they function.

Castellano-Hinojosa et al. 2024 – Graphical Abstract

But you know how we mentioned common knowledge earlier, well here’s the challenge to that. Most readers of this article are probably familiar with beneficial organisms that are naturally present in the soil or can be purchased and applied, often referred to as “bug in a jug” products. Some of the most common products available contain various species of Bacillus bacteria or Trichoderma fungi. These researchers found that the abundance of Trichoderma was increased after treating the soil with chloropicrin, even more than the untreated. Yes, you read that correctly. The abundance of Trichoderma was greater after treatment with chloropicrin compared to doing nothing and that change persisted until the end of harvest. A similar pattern was observed for Bacillus and Paenibacillus species, both of which serve beneficial roles in the soil.

Soil fumigants play a critical role in many production systems and are a necessity to manage major yield limiting pests. However, are these the only uses for soil fumigants? Based on this University of Florida research, could we use chloropicrin, a soil fumigant, to increase the abundance of naturally occurring beneficials like Trichoderma? Could a soil fumigant be used in the role of a bio-stimulant? That would certainly be a challenge to conventional wisdom.

Feel free to contact us to discuss these ideas further and to learn more about what chloropicrin could do in your field.

  1. Ref: Castellano-Hinojosa A, Karlsen-Ayala E, Boyd NS, Strauss SL (2024) Impact of repeated fumigant applications on soil properties, crop yield, and microbial communities in a plastic-mulched tomato production system. Science of the Total Environment 919: 170659; doi: ↩︎

Low Dose Chloropicrin – When SweetPotato Set is at Stake

We hinted at the end of our blog article – 2023 Trial: Impacts of Soil Fumigation of Tobaccothat we also did trials on sweetpotatoes that compared mixtures on Enterolobii nematode control and dual applications on seed production. Track number 1: why high why nematodes? Answered further in this article. Track number 2: why did we get late season resurgence?

In this blog we will go into more detail on those trials, the outcomes, and the implications.

In the Summer/Fall of 2022 TriEst Ag Group did a mixture study that focused on Enterolobii in Nash County, NC. The trial evaluated the use of TELONETM, C15, and C35 at 6 GPA (22 GPA broadcast) shank applied in-row 14” deep with 10” of stack. The row was re-shaped to 5-8” in front of planter. The field had a heavy Enterolobii (Guava Root Knot Nematode or GRKN) pressure.

We fumigated the field May 11, 2022, the field was planted June 14, 2022, and harvested October 24th, 2022.

This chart shows that Guava Root Knot Nematode (GRKN) resurged in all 3 plots. Damage was observed in all plots as well, but was worst in C35, which would be expected from the treatment with the least amount of TELONE being applied.

Despite C35 having the worst GRKN levels and damage it still provided the highest yields and the best crop throw showing a clear benefit to having Chloropicrin in the system. For this growing region that is focused on table stock production, bushes of #1’s per acre is critical.

The results of this trial left us with a significant observation and question, why did we have the highest yield in a treatment with the highest volume of nematodes at seasons end?

Nematode pressures rose in the last 30 days of the crop, even with very good suppression of the pest after each treatment application. Why did we see a late season resurgence of nematodes? How mobile is GRKN and are they moving from untreated areas back into the root zone? Would a deeper application work? Would a wider area of application make a difference?

While we answer the question of why did we have the highest yield in a treatment with the highest volume of nematodes at season’s end in this article the remaining questions this trial spurred we will answer in a future article on another field trial from 2023.

Back to the impact of chloropicrin…

The following summer/fall of 2023 we decided to look at TELONE and TELONE with PIC applied in a dual level application to see if we could build off of what we learned in the 2022 trial.

The trail took place in Nash County, NC again, but this trial purposefully had low root knot nematode pressure. The primary goal was to see the impact of Chloropicrin on the crop and build off of what we learned in 2022.

The sweet potato crop in this trial was grown for seed, where growers are targeting heavier tuber sets and smaller size profiles overall, which is what we saw in the 2022 trial harvest.

We fumigated 6/3/2023 with TELONE at 6 GPA in-row (22 gallons broadcast) and TELONE at 6 GPA in-row plus 20lbs PIC100 (75lbs broadcast) in a dual application 8” PIC and 14” TELONE. Everything was shank applied in-row with a ripper bedder at 14” with 10” of stack. The row as reshaped to 5-8” in front of the planter.

The field was planted on 6/23/2023 and the crop was harvested on 10/20/2023.

The conclusion from this trial was that the addition of a low dose of Chloropicrin (75lbs Broadcast/20lbs BER) increased the tuber set. This resulted in a higher yield and smaller size profile overall. This is a big advantage for seed growers. We feel that getting the Chloropicrin dose as close to the where the root system will be (6-8” beneath final planting depth) is important. For nematode management, TELONE should be applied 12-16” deep to treat the highest volume of soil possible, which is why we looked at dual application as opposed to a blend with both products being applied down deep.

In conclusion, the key takeaways from these trials would be that higher sweet potato yields can be achieved when a low dose of Chloropicrin is used to increase set. TELONE is critical for nematode management and depth of application is important in regards to location of the pest in the soil profile. Dual level application with Chloropicrin applied in the root zone and TELONE applied beneath the root zone increases tuber set while also maximizing nematode management.

Remember to subscribe so that you don’t miss our future blog article on our work in sweetpotatoes that will answer the questions of why did we see a late season resurgence of nematodes? How mobile is GRKN and are they moving from untreated areas back into the root zone? Would a deeper application work? Would a wider area of application make a difference?

To learn more now or talk to a representative about seeing what Chloropicrin can do in your field Contact Us Here.

2023 Trial: Impacts of Soil Fumigation of Tobacco

In our last post we covered the Impacts of Fall & Spring Fumigation of Tobacco.

Based on the findings from those trials in 2021 and 2022 TriEst wanted to take a deeper look at finding unique application and timing solutions to better meet a grower’s nematode and disease pressures. The 2023 trial focused on sampling depths to map location of pests, dual depth applications to place the correct product in the right place, and a variation of treatments to proof out these concepts.

We prepared different application levels to best place TELONE™ and Chloropicrin where nematode problems were the previous season at depths of 12” to 18” due to cool soil temperatures in early spring driving nematodes down to more temperate soil levels. In the Fall, nematodes are up high in the soil profile due to warmer soil temperatures and available food sources from crop roots being grown through the summer. Fall is a challenging application time for tobacco growers due to harvest of tobacco along with rotational crops and timing of crop contracts for the next season. In most cases, growers haven’t finalized plans for planted tobacco acres for the following season until late Winter. This makes finding a Spring application solution critically important.

Soil samples were pulled monthly throughout the season at dual depths of 0” – 8” and 9” – 16” from both in the row and the row middles. This sampling protocol allowed us to map the movement of nematodes from deeper in the soil profile up into the root system, as well as from the row middles into the row. Shown below in the soil samples. The darker color soil (right) is from the deeper level of 9” – 16”. Note the soil type differences in the soil probe and final sample collection bags, this visually highlights the potential need for dual application, as nematodes in the Spring are concentrated in the deeper soil profile (9-16”) and soil borne pathogens in the shallower soil profile (0-8”).

We designed an application strategy that would place TELONE™ and Chloropicrin within the soil sample zones described above and compared the dual depth application to the grower standard single depth application on the bottom of the shank. All applications were made in-row treating 25% of an acre, with a 12” application zone on 48” row centers. See the picture below, the top outlet is 8” below the soil line and the bottom outlet is 14” below the soil line. At the time of application, there will be an additional 8-10” of soil stacked on top during the bedding process.

Unlike our trial in 2022, this trial didn’t show a late season nematode resurgence. Pre-fumigation root knot nematode levels warranted treatment, but all treatments cleaned up this issue. We expected additional nematode pressure to come from the row middles and to move up from below our application depths, which happened in 2022. Yields were not impacted by nematode pressure; however, they were heavily impacted by Grenville Wilt. The significant differences you see in yield in the chart below between the non-treated check and all other fumigant treatments are due to early season growth responses from Chloropicrin and suppression of Granville Wilt. All fumigant treatments performed well over the non-treated check, with little separation between the grower standard of PIC100 at 50 lbs/acre and the additional treatments including TELONE™. Again, this was a result of lower than anticipated root knot nematode levels from mid-season through harvest. The highest yielding treatment was the dual depth application of TELONE™ and Chloropicrin, likely due to getting Chloropicrin closer to the root system of the plant with a shallower application point than the grower standard treatment.

Guava Root Nematode pressures are rising in sweetpotatoes so we did a similar trial that compared in-row vs broadcast applications at different depths with high/low sampling. Unlike the tobacco trial of 2023 the pests showed up to dinner.

Be sure to subscribe to our blog so you don’t miss the details on the sweetpotato trial and other trials.

If you’d like more in-depth information on our trials and what TriEst can do for your farm be sure to reach out to us. Contact Us Here

You can also view a video from the 2023 Tobacco Field Trial on our YouTube Channel Here.

Impacts of Fall & Spring Fumigation of Tobacco

This project was established in East Central NC originally in 2021 to evaluate the effects of TELONE ™ II and Chloropicrin (PIC) on nematode suppression, Granville wilt suppression, and tobacco yield and quality.

Yield losses from crop “melting” late season have become common in the greater tobacco production regions. This is a complex issue of harvest timing, weather conditions, disease, and nematode pressure. Growers are consolidating and getting larger with same infrastructure, which is putting more pressure on fumigants to protect the crop longer. Companies also want more overripe tobacco, putting more pressure on late season harvests.

In tobacco, maturity windows are critical to management, when everything matures at once and growers struggle to get around the crop and harvest in a timely manner. In 2021, our first tobacco blend study resulted in the grower standard of 200# PIC (#50 BER) being the better treatment overall with more early vigor than treatment blends containing TELONE. The plots with PIC100 showed a 5 to 7 day earlier maturity rate over PIC/TELONE blends, leading us to the question of – is it possible to stagger harvest between the products?

If PIC is maintaining earlier maturity, that needed to be accounted for in harvest planning. We consolidated our 2021 findings into our set of treatments for the 2022 tobacco study with another central North Carolina tobacco grower. Similar to 2021, treatments containing only Chloropicrin (PIC) in the Spring showed the best early vigor, highest lower stalk yields, and overall best plant structure.

Once harvest began, we found that late season nematode pressures resulted in higher wilt levels and caused yield losses. There was not much separation between the Spring PIC100 and PIC60 plots in nematode control (Spring application, cool soil temps, and depth of pest may have played a role). Spring PIC application plots looked best prior to nematode pressure and had the best first and second harvest yields. In instances where Root Knot Nematode isn’t present PIC100 is the most economical solution.

All of the plots where TELONE was Fall applied had a significant impact on season long nematode suppression and resulted in the highest yielding plots overall. While Fall applied TELONE treated the late season nematode problem and protected yields, it didn’t necessarily cause the yield gains. The Spring PIC60 application didn’t solve the late season nematode problem. Knowing nematode levels and location in the field pre-soil fumigation is critical.

Based on these findings TriEst’s intention is to take a deeper look at finding unique application and timing solutions that meet a grower’s needs. We have more trials in the ground now improving on soil fumigation application timing and depths. Our next blog will be on our 2023 trials that focus on sampling depths, the probes, and treatments. In the 3rd blog of this series, we will go over those 2023 trial results.

So stayed tuned and be sure to subscribe so you don’t miss the latest information.