Field Trials of Organic Herbicides in Vegetable Production

Final Report for FNC06-609

Project Type: Farmer/Rancher
Funds awarded in 2006: $17,600.00
Projected End Date: 12/31/2008
Region: North Central
State: Indiana
Project Coordinator:
Dale Rhoads
Rhoads Farm
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Project Information


Rhoads Farm is a three acre hillside certified organic vegetable farm that concentrates on leafy greens, herbs and fruit. The farm is a husband/wife team that has been in operation for 12 years. They grow for area restaurants and a local food cooperative.

Cinzori's Family farm is an organic farm in southwest Michigan and is the largest organic vegetable farm in Michigan, growing 35 acres of organic vegetables. The Cinzori's sell their produce to restaurants, retail outlets and farmers markets. They also grow organic greenhouse transplants and herbs for sale. The Cinzori's have been farming organically for 20 years.

Tiwald’s Green Earth Institute is a CSA located near Chicago, Illinois. This is a father/son operation that currently farms around 5 acres. The Tiwald’s run many educational and community service programs at their farm which is surrounded by suburbs.

All three farms regularly employ sustainable farming practices like crop rotation, erosion control, organic production, family and community involvement, soil enrichment, cover cropping, etc… and have done so for the life of the farms.

For the past several years Rhoads Farm in Indiana has been experimenting with and making use of in the field organic herbicides and flaming in creating a sterile seedbed. Doing this has created with certain crops a 75% reduction in weeding costs. In 2006 Steve Tiwald of Green Earth Farm in Naperville, IL and Anthony Cinzori of Cinzori family Farm in Ceresco, MI joined with Rhoads in performing formal trials of the effectiveness of the different herbicides that are available on the market. That 2006 SARE Group Project also included some informal in-field testing of these techniques. This current grant proposal is for applying what has been learned in prior years about these herbicides and how they work into direct field trials.

The purpose of this is to demonstrate and explore various ways these herbicides can be used on various crops on organic farms to give yet another strategy or technique in organic farming weed control methods. And to provide a clear cost analysis of these methods to more conventional weed control strategies.

Over the two years of field trials adjacent plots were set up to test hand weeding compared to organic herbicide use in the following crops:
1. Salad greens
2. Cilantro
3. Spinach, arugula and other small leafy greens
4. Head lettuce
5. Carrots
6. Broccoli
7. Sweet corn
8. Squash
9. Kale
10. Tomatoes

Records were kept for labor and materials in the 40 test plots over the two years.

The following is a summary report of the different trials.

Organic Herbicides
An organic herbicide is a compound that has the ability to kill some weeds, especially in the immature stage, that is derived from naturally occurring or non-harmful materials. These herbicides are ‘contact’ herbicides rather than ‘systemic’, which means they kill weeds by damaging the cell structure of the plants they come in contact with. (A systemic herbicide like the non-organic Round-up kills by disabling the plants ‘system’ or internal functioning.) Most of these organic herbicides are OMRI approved ‘restricted products.’

After testing and using these products along with LP Flaming for over six years on Rhoads Farm, in trials with a university researcher and two years of trials with other Midwest farmers we have some conclusions to share. These conclusions are briefly stated here:

1. Like with any new product the farmer has to have a need and a willingness to learn the products in order to best make use of their effectiveness.
2. These herbicides do not kill all weeds under all conditions and have to be learned for their strengths and their weaknesses.
3. Careful timing of the use of the herbicides is essential, especially for creating stale or sterile seedbeds.
4. Weather conditions are important for the best kill rates. Cloudy days without rain are actually the best as more UV is trapped in the atmosphere.
5. There is resistance with many organic farmers and researchers to using an herbicide because it is reminiscent of chemical farming technologies. These products can be very effective with certain crops under certain conditions, are approved for organic use and have no toxic affect on soil, other plants or the environment.
6. These products work best on immature weeds under 4” in height.
7. There are some crops in which these products can greatly cut down on weeding time. These are crops like salad greens, spinach, cilantro and other short season direct seeded crops that are grown in close rows or beds with rows 4” or so apart. There are other crops in which other weed control strategies are much more efficient. These crops tend to be the longer season and more spread out crops in which multiple weedings are needed.
8. Many organic farmers are not familiar with sprayer technologies and equipment use.

To conclude this introduction, I want to say that at Rhoads Farm we make daily use of these products and technologies for setting up a stale seedbed on most crops and as the primary weed control strategy on salad greens and other short season leafy greens. Doing so has dramatically reduced our weeding time, hence increasing profits both through effectively reducing weeds and freeing up time for other farm tasks.

Organic Herbicides and Technologies Available
* Matran 5- Matran 5 is an essential oil based product that comes in concentrated form. This product works very well. Like all of the organic herbicides it will only kill very immature grasses and at higher concentrations of product. It is our commercially produced product of choice.
* Weedzap- While it has some differences chemically from Matran it is similar. It kills weeds in the same range of effectiveness. It is not quite as concentrated as Matran which can add to shipping charges. Our research partner in Illinois who deal with a different set of weeds prefers Weedzap based on his field trials, but Matran was a close second.
* Racer- We have only done one year of testing with Racer. We are impressed with its results as it is in the same range or maybe even more effective as Matran and Weedzap, but is more costly.
* Alldown- This product is premixed containing substantial amounts of vinegar and citric acid. Although the label does not suggest diluting the product we have tested it at 25% and 50% product dilution rates. At the 50% dilution rate it will kill hairy Galisoga and other broadleaf weeds like lambsquarter etc… Our experience is it performs poorly on grasses and more succulent weeds like purslane. For us because it is not as effective as the above three and comes pre-mixed it is in our judgment best used for smaller application areas with the more easy to control weeds when shipping costs are not prohibitive.
* Apple Cider Vinegar- Across the shelf vinegar is 5% vinegar and 95% water. Commercial vinegar can be obtained across the U.S. from local or more national food suppliers. It comes in 50 gallon drums at 20% vinegar. We use and have tested vinegar in ranges from 7- 20%. We regularly use a 10% vinegar solution to kill immature hairy Galisoga and lambsquarter, pigweed etc…with great effectiveness and very good cost effectiveness. At the higher dilution rates vinegar can kill purslane, sometimes. It has little impact on immature grasses.
* LP Flaming- Simply put LP flaming is the best killer of weeds and the most cost efficient. It is also less messy and time consuming to use. We use a Red Dragon back pack but larger applications and appliances have been used in row crop farming for many years with good success. The draw back is it is non-renewable. But then so is the energy used in producing organic herbicides and organic farming in general and the transportation of farm products. I use my flamer, especially if the weather is detrimental to herbicide applications.
* Sheet Plastic Solarization- We regularly make use of 10’-15’ by 100’ sheets of clear four year greenhouse plastic. In the spring we will till an area, spread plastic to warm the soil, better germinate weeds for later kill with an organic herbicide or flaming and to keep the area dry enough to plant in when soil temperature reach the level of germinating seed. One of the side benefits of doing this is that often soil temperature will go above the seed germination range for chickweed, which the herbicides do not do a good job of killing as they just re-grow after the tops have been killed. We also sometimes use plastic to keep our soils from over compacting due to heavy rains during the two weeks or so while allowing weeds to germinate to set up a sterile seed bed. At times in the summer we have experienced almost total weed kill from solarization and plan on doing some more formal studies with this technique.
* Ultraviolet light- There are some products out there that use light waves in an intensity and wavelength that kills plants. We have no personal experience with these products but think that as cost goes down this technology could become a very good weed killer, very cost effective and better energy resources use than many of the other options.
* Hot Water- We have never tried using boiling hot water but know of a nursery man who uses this technology with great effectiveness. It entails using, probably a non-renewable energy source, to heat water to boiling, put it in a sprayer to spray as quickly as possible so as hot of water as possible is delivered to the weeds. This nursery man heats and uses 50 gallons at a time. There are large scale use tractor mounted hot water sprayers.

Case Studies
As a better way to explain some of these uses for organic herbicides, I am going to present some brief case studies.

Rhoads Farm- Central Indiana
At Rhoads Farm we have minimal amounts of space with little land that lies fallow with a cover crop giving weed seeds a chance to die. Half our income comes from salad greens. From all of our growing areas we have virtually eliminated all weeds except Hairy Galisoga, purslane, chickweed and one small unidentified grass. Leaving out the chickweed all the other weeds we experience pressure from have the same characteristics. They have long lasting seed life, germinate and come to seed quickly and are vigorous seeders. These characteristics lead to these weeds, especially Hairy Galisoga becoming a serious threat to our farm profitability. We saw weeding time on our salad greens climb yearly, again becoming a serious problem with farm profits due to increased weeding time.

In discussing this problem with a Purdue University Extension Specialist she told of having been given some organic herbicides to trial and offering the use of them for trials. I rejected her offer because Organic Farmers do not use Herbicides! Several weeks later weeding Galisoga I reconsidered the offer. By learning to properly use thee products we have cut weeding time on our salad greens, spinach and cilantro by 90%. Today we set up a stale seedbed with almost all of our crops virtually eliminating the first seeding on bare ground crops and mixing use of the herbicides with mulching etc… to greatly reduce our time weeding. We continue to do cost effectiveness trials with other crops and mixing herbicide use with other weed control strategies to increase our farm productivity. We had the motivation and the willingness to learn how to put these products and technologies into our faming system

Green Earth Institute- Northern Illinois
Steve and Nathan Tiwald, a father son team farm 10 acres doing a CSA. They have participated in two years of trials with the organic herbicides. From those trials they have determined that the use of the organic herbicides is more expensive than hand weeding. There are several factors worth examining to explain the difference between their results and the results at Rhoads Farm.

Mr. Tiwald reports, “The weeds most commonly found growing at the Green Earth Institute farm are Canada thistle, dandelion, foxtail, horsenettle, lambsquarters, pigweed, smartweed, sow thistle, yellow nutsedge, and velvet leaf.” These contact herbicides will not kill the thistles, dandelion, smartweed, nutsedge and foxtail because those plants, even in the immature stage have enough root growth to suffer a die back of foliage only to re-grow.

The second factor is the choice of crops used for testing, in 2007 carrots and broccoli. Both of those plants do not throw enough foliage soon after germination due to spacing or the nature of the plant to shade out sun on possible weed seeds. This is a different environment than the salad greens, cilantro, spinach etc… that Rhoads use with these products. These crops are planted closely together and within two weeks provide complete shade over the growing area allowing for very little ‘secondary’ weed growth.

A third factor at Tiwald's farm is that they have to buy water, hence use drip irrigation to reduce watering costs and all crops like salad greens are started in seed trays and transplanted out. While a sterile seedbed would assist with reducing weeding pressures the act of transplanting restirs the soil, exposing new weed seeds and cutting down on the effectiveness of using a sterile seedbed with direct seeded crops. Because of the cultural considerations this means the very crops that can best be assisted by these organic herbicides in giving the greatest return on the money are eliminated. Rhoads standard technique is to germinated weeds for 1-2 weeks depending on the season. Direct seed high dollar, short season, closely planted crops right into the 2-3” tall weeds and do the weed kill the day before germination of the crop.

A fourth factor that reduces the effectiveness of these techniques at Green Earth Institute is knowledge of the different herbicides and approaches. Timing is critical to get the best results and to turn a hard weeding job into no weeding. One of Tiwald’s trials this year was essentially abandoned due to rainy weather making application of the herbicide’s impracticable. In that situation at Rhoads Farm we use the LP burner which can still provide excellent weed kill in wet conditions that a contact herbicide would wash off before killing the weeds.

A fifth factor that helps explain the difference in Rhoads and Tiwald’s assessment of the effectiveness of these herbicides in a stale seedbed is weed density. Tiwalds use good rotation practices based on having 50 acres to keep in permanent cover crops that they only grow vegetables on 10 acres of. This makes for a much lower weed density rate than the 75%-100% weed densities Rhoads experience with Hairy Galisoga. The Rhoads have to kill those weeds to even get the crop to germinate correctly.

Discussing the factors in these two farms makes explaining the use of these herbicides and the on-farm factors in which they provide the most return on the dollar dramatic. I have written this several times in this report: Weed type, crops grown, cultural practices, flexible approach to timing with knowledge of the product and weed density all are factors to consider in using these products in the most cost effective manner.

Michigan Research Partner
Cinzori Farms grows 30 acres of organic vegetable crops every year. His research assistant was a row crop extension specialist who does work with organic row crops especially with cover crops.

This farm is successful, big and very busy. Although weeding costs in crops like salad greens is a concern, within the total farm picture it is not a serious limiting factor to farm productivity. In the overall farm picture weed problems with salad greens starts to take a small importance and becomes one of the important things dropped from the essential list that occurs on every farm.

They also have a readily available, reliable and relatively inexpensive workforce of immigrants that they can pull from making labor costs much lower than what Rhoads or Tiwald’s experiences. At this farm they know that used properly these products could be very beneficial for growing of salad greens, but just do not have the time or motivation to learn to use them correctly and the needs of the farm do not demand at this time they do so.

Case Study Summary
Labor availability, type of crops grown, overall farm needs and available time to learn new techniques and change cultural habits to improve farm profitability, attitudes towards using a herbicide in organic production, water availability and watering practices and learning the products are the most important factors in whether organic herbicides and or LP flaming can improve farm profitability by reducing weed pressure and reduce labor costs or improve crop yields.

It is interesting to note that Rhoads Farm, probably one of the longest running and most sustainably operated Midwest organic farms, has received criticism from other organic growers for even considering using an organic herbicide.

Our history with the herbicides is that we had 6 years ago began to experience increasing pressure from hairy galisoga that was severely limiting our salad greens production while almost all other weeds had been eliminated from our fields. When offered by an extension educator the opportunity to try some organic herbicides we turned down the offer because it was an ‘herbicide.’ Several weeks later in re-thinking the offer we began experimenting with the herbicides and got great results dramatically reducing our weeding time. We have gone on to study how these products can greatly improve farm profitability if used correctly.

It is also interesting to note that we have experience with some other farmers trying using these techniques and not being able or willing to learn the products or change their cultural habits and reported losses and they still had to do all the regular weeding they would have had to do other wise.

One typical story is a local farmer who asked about these techniques, was recommended to use herbicides, instead bought a LP flamer and when they almost burned up some crops that were mulched with straw were less than happy with the techniques. The old saying, “you can lead the horse to water, but you cannot make them drink’ seems to apply. Today they are still hand weeding.

Cost Analysis
Setting up a sterile seedbed costs under $20 in spray materials and labor for a 3’ by 100’ growing area. In a leafy greens growing bed this can accomplish what at minimum wage would be over $100 of hand weeding. The various factors that affect the cost of weeding have been extensively explained in the above paragraphs.

Application in Other Crops
A number of trials were done with crops other than salad greens and some comparisons to other weed control methods were done. Below is a summary of these trials.

Sweet Corn- Several trials were performed over three growing seasons in which sweet corn was planted into a sterile seedbed created with an organic herbicide and then season long weed control was maintained with a combination of organic herbicide or LP flaming. These plots were compared to hand and mechanical weeding plots. After the sterile seedbed, four additional applications of organic herbicides was used as the only weed control and gave sufficient weed control for good crop yield with no weeds producing seeds. The labor time in the herbicide plots was approximately 1/16 of the hand weeding and the costs were approximately 1/8 of the hand weeding. But it has to be noted that the weeds in these plots were all weeds that the herbicides could kill and weed seed formation was beginning at harvest time in this short season corn and at harvest the entire area had to be immediately mowed to keep weeds from forming seeds. With a longer season corn it might have been essential to do an additional spraying. With this the weeds were at one point allowed to grow with the calculation of the corn would come to harvest before weed seed production would mature. The herbicide plots were not as ‘clean’ looking as the hand weeded plots, but again, no weeds were allowed to produce seed.

An Indiana farmer not associated with these trials reported to me in 2008 that he grew 10 acres of sweet corn using apple cider vinegar spray applications as the only weed control method. He did know how or of the technology of sterile seedbed but still got good results. He reports that he did four applications of full strength commercial grade apple cider vinegar (20% vinegar as compared to 5% in the retail stores.) He states that this controlled all weeds including hard-to-kill grasses. He states that this was cost effective and no weeds seeded. It could be that he could have achieved the same weed control with a more dilute concentration yielding even better cost effectiveness.

Kale- Kale was grown with several different weed control strategies including using only herbicides, hand weeding, mulching and combinations of the three. The use of the herbicides in setting up a sterile seedbed to transplant into and using the herbicides to control weeds that germinate through mulch seem to show good promise in cost effectiveness. Using them as the only method of weed control is not as cost effective but when compared to labor of mulch applications, cost begins to be about the same.

Summer Squash- Several years of trials were performed comparing three different weed control methods and comparing yields. The methods were using three applications of an organic herbicide, hand weeding, planting into a crimped over wintered cereal rye cover with herbicides used to control later season weeds and a heavy mulch. The most cost effective was the herbicide plot, but there were some weeds that matured seeds as herbicide applications could not be done once the squash leaves covered all the ground. Spot hand weeding could have addressed these weeds. The most productive with the least weed pressure was the mulched areas, but they were also the least labor cost efficient. The squash planted into the crimped over with herbicides used to control weeds was very labor efficient but had poor yields thought to be because of summer squash cultural needs of a loose soil.

Tomatoes- Several years of trials were performed using plastic mulch, an annual rye grass undercrop to control weeds, organic herbicide control and hand weeding. The results of these informal trials appear to show that the plastic treatment is still the most cost effective with the best weed control, but clean up and plastic disposal eats into those savings. The herbicide plots that were hand weeded as the plants matured seems to be the most cost effective and environmentally sustainable method. The annual rye grass did not give suitable weed control, mostly due to insufficient germination due to insufficient watering in this drip watered tomato plants.

We had many co-operators including other farms and university personal from Indiana, Michigan and Illinois. These are the members of the New Ag Network (NAN) and their names are listed on the NAN website:

Whether the use of an organic herbicide can be of benefit to any farm is dependant on many different variables including the density of the weeds to be killed, the types of weeds, the crop grown, farmer knowledge and cultural practices and other factors that have been discussed in above sections.

Many different factors have been discussed in above paragraphs.

Two of the farms had field days in which over 75 people combined saw these trials.

All of the farms had extension educators aware of or participating in the trials so there is a wide distribution of the information in the extension educator network. Some of the farms participate in bi-weekly conference calls involving farmers and extension educators from up to five North Central SARE region states. These trials were talked about and discussed during these conference calls. Members of the extension educator states include Indiana, Illinois and Michigan.

In 2007 there was a progress report of results made available on our New Ag Network website, which has over 100,000 hits from educators and farmers a year.

In 2007 Rhoads informally presented results at one of the forums at the Indiana Horticultural Congress and an organic seminar.

In 2007 Rhoads participated in a three-state live video feed university program for farmers, by other experienced farmers and university personal, highlighting these trials, how to use organic herbicides and other organic weed control strategies. Several hundred people paid for and attended these programs at their local extension educator’s office and recordings were made for future archived use.

A final report will be filed on our NAN website by the end of 2008 or early 2009 depending on university personnel time availability around the holidays to get it on the site.

In 2008 Rhoads will be assisting in a program at the Indiana Hort Congress about educating selected extension educators on supporting organic farming. Rhoads will pass out a one-page highlight of these trials to those educators who are most involved in organic farming in the state of Indiana.

We are very happy to have participated in this SARE project and have no criticisms or comments other than our thanks for this program and the administrators and employees of it.


Participation Summary
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.