Development of Organic Weed Control Strategies

Final Report for FNC05-582

Project Type: Farmer/Rancher
Funds awarded in 2005: $17,896.00
Projected End Date: 12/31/2007
Region: North Central
State: Indiana
Project Coordinator:
Dale Rhoads
Rhoads Farm
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Project Information


Rhoads Farms 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 local restaurants and organic retail outlets.

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 farm is a diversified vegetable operation in the western suburbs of Chicago, growing 40 different vegetable and herb crops for their CSA. In 2006, their fourth year of operation, the father and son team had 6 acres in vegetables and the remainder of the 60 acre farm in cover crops.

Rhoads and Cinzori are officially certified organic, and Tiwald is in the application process. All three farms have engaged in sustainable practices like soil building, cover crops, minimum tilling, IPM pest management, water conservation practices, serving local customers and community education from their inception.

Our project goals, paraphrased from the proposal and elaborated on from our project experience are:
1. Gather information for the proposed 2007 Organic Vegetable Growers’ Weed Management Manual.
2. To evaluate organic strategies for creating a sterile seedbed. This is broken down into two compoenets:
a. Evaluate the effectiveness of LP Flaming and the Organic Herbicides now available for their weed kill ability.
b. Familiarize the farmers with the use of these products and possible ways to use them, which include creating a sterile seedbed and also other techniques.
3. The third goal was to do a weed control strategy inventories on each farm and the network systems we are involved in for the purpose of exploring possible improvements to be tested, experimented and researched in subsequent years.
Goal 1. Gather information for the proposal 2007 Organic Vegetable Grower’s Weed Management Manual.

All of the three farmers in this project belong to a multi state (Illinois, Indiana, and Michigan) organic farming network. The New Ag Network ( was established in 2004 to improve organic practices. This network provides a forum for information exchange between farmers, Extension educators and researchers. In 2004-05 Michigan State University Extension produced a bulletin on “Integrated Weed Management” using a similar group effort writing format. It is our intent to write a similar bulletin about Organic Vegetable Production Weed Management. There are several new exciting weed management tools and strategies that we are trying to study and implement over the next several years. These Organic Herbicide trials and uses are a small part of the new weed management strategies. We are using these trials and the trials proposed for next year to provide the information for the herbicide portion of the bulletin. We now are not planning on writing that bulletin in 2007 because of the need for further studies.

While answering this question I will go ahead and list some of the other people of our New Ag Network (NAN) who have participated in this project or have been involved in discussions or information sharing about it.
Dale Mutch – Extension Specialist, Michigan State University – assist Cinzori
Liz Maynard, PhD – Extension Specialist Purdue University
John Masiunas, PhD – Associate Professor U of IL, weed management specialist
Maurice Ogutu – Extension Specialist U of Illinois – assists Tiwald in trials
Deborah Cavanaugh-Grant – U of IL Agroecology/Sustainable Ag Program Fifteen Organic Farmers from the three states.

For this goal of gathering information for the proposed bulletin, we have gathered the information as to which of these herbicides worked best in this year in what concentrations and with what weeds. Those findings will be presented under the discussion of answering another goal.

Additional research is still needed into how much benefit and the cost savings, if any, the use of these products and techniques can give in what crops under what kind of weed pressure, in order to provide accurate information for other farmers. We have proposed a SARE grant to answer those questions in 2007.

Goal 2. To evaluate organic strategies for creating a sterile seedbed. This is broken down into two components:
A. Evaluate the effectiveness of LP (liquid propane) Flaming and the Organic Herbicides now available for their weed kill ability.
B. Familiarize the farmers with the use of these products and possible was to use them, which include creating a sterile seedbed and also other techniques.

Let’s begin with answering the first portion of that goal:
A. Evaluate the effectiveness of LP (liquid propane) Flaming and the Organic Herbicides now available for their weed kill ability.

Random block design replicated trials of all of the known available organic herbicides were performed three times during 2006 in each state to test weed kill effectiveness.

The herbicides tested were:
- Matran EC-Clove and wintergreen oil, tested at 5-6 and 10 oz/ga
- Weedzap – Clove and cinnamon oil, tested at 4 and 8 oz/ga
- Alldown – Citric acid, garlic, acetic acid, tested a full strength and 50%
- Apple Cider Vinegar – tested at 10% and 20% acidic acid strengths
- LP Flaming
(The manufacturer of Alldown does not recommend diluting their product. At Rhoads Farm 50% Alldown kills Hairy Galisoga under 2” in size. Apple cider Vinegar in the grocery store is 5% dilution, 20% dilution is the strongest it can be bought in.)

Results were widely varied, but recognizable trends of effectiveness can be seen. At Rhoads Farm in Indiana they received 100% weed kill with all the products and flaming in two out of three trials and better than 85% weed kill with most of the herbicides in the third trial with harder to kill weeds. In Michigan the trials were done with larger weeds due to rain, product availability and testing personnel being able to gather. Significantly lower application rates were used in Michigan which explains the much lower weed kill rates they experienced. Green Earth Farm in IL experiences less weed coverage, with harder to kill weeds. Rhoads, who has the most experience with these products and was using the testing areas to grow actual crops, has virtually eliminated the harder to kill weeds from their fields which make for better kill rates with the herbicides. In their second trials there were some grasses and Purslane, which are harder to kill, unevenly distributed throughout the test plots.

All the numbers in the following table can be slightly skewed due to various field conditions which include:
- Uneven application of materials
- Uneven distribution of hardier weeds
- Different weeds at different farms
- Size of the weeds
- Unfamiliarity of handling products

However the table does show general trends that seem to be close to actual field use seen at Rhoads Farm. Of interest is exactly what herbicides kill what weeds. It appears as a general rule that the products containing Vinegar kill some grasses better than some of the essential oil based products. At Rhoads Farm the essential oil products like Matran and Weedzap kill the one grass species more effectively than vinegar.

[Editor’s note: there are tables that could not be posted online. If you would like to see these tables please email us at [email protected]. Thanks]

At Rhoads Farm, where Hairy Galisoga is the main weed, all of these products are very effective at producing a sterile seedbed to plant baby greens, carrot, beets and similar crops. We regularly make use of all of these products depending on what weed, what size weed, time of the year, weather conditions and other factors experience has taught us. We try and tailor the herbicide to the need. Generally on our farm, for our weeds (Hairy Galisoga, one very short unidentified grass and Purslane) we would consider the following list of what is the most effective weed killer.

LP Flaming – we do not like to use it because it is a non-renewable resource
Matran @ 10oz/ga
Weedzap 8 oz
Alldown and vinegar 20%
Matron 5-6 oz
Weedzap 4 oz
Vinegar 10% and Alldown 50%

In most applications and most seasons at our farm Vinegar 10% and Alldown 50% are sufficient to provide 100% weed kill in creating a sterile seedbed with weeds under 2”.

If we drop Cinzori’s Michigan trials the results look like this table, which is much closer to what is experienced typically at Rhoads Farm in production use.

[Could not be posted]

As shown in the table, flaming does the best job. Weedzap at 8 oz per gallon, Vinegar at 20% and Matran EC all perform similarly. Then Matran, Weedzap and Vinegar at the lower concentrations are similar. (At Rhoads the Vinegar is the weakest of those three). In these trials Alldown at full strength performed the poorest, but it is an efficient killer of some weed species and we use it at Rhoads Farm in certain applications.

The second part of goal 2 was:
B. Familiarize the farmers with the use of these products and possible ways to use them, which include creating a sterile seedbed and also other techniques.

In fulfilling this goal here are some of the activities we did:
Two of the farms did supplemental experimentation to the replicated trials using the products and techniques in actual crop conditions. The third farm did some experimentation but poor weather in the fall prohibited fulfilling the entire amount of hours named in the contract.

At Rhoads Farm in Indiana they did numerous plantings with salad greens over the growing season using these products and can report on those. They also did some side experiments with Alldown to determine whether it could be diluted, which the manufacturer does not recommend. They did trials with using herbicides to control weeds in setting up kale beds and weed control in the kale later in the season. They used these techniques in the growing of multiple beds of cilantro and other herbs. They used the herbicides in setting up a late season spinach bed. They did some experiments with using herbicides and LP Flaming to control weeds in sweet corn. Some brief demonstration of how these products cannot handle mature grasses.

At Tiwald’s Green Earth Farm in Illinois after doing some of the trials they began to gain some familiarity with these products. They did three in field experiments using the herbicide Weedzap. These informal trials were of one 500 ft. strip of beets, 4 rows, direct seeded. Spinach: one 350 ft strip, 4 rows, direct seeded. Lettuce: parts of one 500 ft. strip, 4 rows. Transplanted seedlings in soil blocks from the greenhouse, at the rate of approximately 400 seedlings every 10 days.

At Cinzori’s Farm in Michigan, Anthony performed trials with grass suppression in between rows of crops in plastic mulch. They also set up several different experiments with field crops but extremely wet fall conditions stopped those informal trials from occurring. They were not able to do the trials or to plant crops. But Cinzori’s have gained enough experience with these products to see the possible use for them on their farm.

There is a little bit of a mental adjustment that it takes organic farmers to go through to begin to experiment with herbicides which smack of conventional farming. And it takes a while to sort of get an idea of what these products can and maybe cannot do. If these products are going to be used organic farmers need some educational time to learn them. This has been accomplished on these farms. Saving other farms times on this learning curve is one of the goals of this project.

Rhoads farm makes use of these products on a weekly basis in their farming operation. Anthony Cinzori in Michigan had some of the trials with the lowest weed kill counts in 2006. Yet this is what he has to say at the end of these trials: “I do, however, feel there is a place on my farm for these products. I think baby greens, spinach ,beets and carrots are crops that I could use products like these tested. In the right soil a stale seed bed system could work really well when the crop is not a very good competition to weeds. I think forming beds, letting the early weed flush grow, seeding my crop into the weeds and then killing the weeds (at a small stage less than two inches) with these products could result in dramatic labor savings.” Anthony also asks: “Is it cost effective?” This is the goal of the planned 2007 trials, to answer that question.

At Tiwald’s farm in Illinois they have some doubts as to whether these products will be cost effective for them but are interested in trialing them with carrots, beets and some other similar in cultivation crops. They have gained enough experience to being asking questions similar to what the other farmers are asking. Below is an example of the kind of questioning Tiwald’s are doing:

The herbicide was effective only on small sized weeds, i.e. up to about 3-4 inches in height. If any weeds had gotten larger than that, the herbicide only sometimes killed them. Often what it did was stunt them through desiccation of the leaves and parts of the stem, but re-growth took place and after a few days the weed resumed full strength and continued growing.

The herbicide generally was not effective on grasses. Control of grasses required hand and/or mechanical cultivation.

The herbicide application that took place just before the vegetable sprouts emerged was effective, but additional weed seeds germinated after the vegetable sprouts were growing, and it was too difficult to spray this second round of weeds without damaging the vegetable sprouts. Control of this second round of weeds required hand and/or mechanical cultivation.

The herbicide applications had an impact on most of the early weeds, but some recovered and continued growing, plus new weeds emerged after the spraying. Because of that, hand cultivation still had to be done. Idea for next time: in order to better defeat the weed seed bank, try to do two, three, or more sprayings before the vegetable seeds emerge. Each successive spraying will destroy a portion of the weeds whose seeds are in the soil. This should greatly reduce the weed pressure on the vegetables. But how many sprayings would this take, and at what cost in worker time and materials, and how much of the growing season would be involved?

A second issue to research by actual effort is comparison of real costs of weed control methods, testing the time and materials used in spraying vs. the time and materials used for hand and/or mechanical cultivation.”

One of the most interesting things we have learned is cultural systems of farms, growing methods and types of weeds experienced are integral parts of determining whether and how to use these products.

Rhoads Farm is a small acreage farm that makes use of all available land every year. They have essentially eliminated all the tougher weeds like thistle, smartweed, most grasses, etc…they experience high populations of several weeds that have very short life cycles able to produce seed within a month from germination; weeds like hairy Galisoga, chickweed and Purslane. These weeds are easily killed with these products. Rhoads largest crops are salad greens and herbs that require close and intensive hand weeding and benefit greatly from a sterile seedbed. These factors of intensively grown crops with high populations of easily killed weeds make these herbicides an ideal labor saver for Rhoads Farm.

Tiwald’s Green Earth Farm near Chicago, Illinois has some differences than Rhoads Farm. Tiwald’s land is in a perennial alfalfa cover crop of many years. This had virtually eliminated many weeds while giving moderately high populations to weeds that are capable of surviving in the alfalfa cover. Many of those weeds like some grasses and Canadian thistle are a little harder to kill. Also their cropping system is different than Rhoads in terms of many crops Rhoads direct seed, they transplant out because with their drip irrigation opposed to Rhoads overhead watering experiences some germination problems. Also they grow a wider range of crops many of which are not so weed susceptible as what Rhoads grow. So this presents a totally different cultural environment.

Cinzori’s Family Farm in Michigan which farms the largest acreage of the three farms presents a cultural climate that could be considered in between the Rhoads and Tiwald’s farm. They experience more weeds that are easy for the herbicides to kill than Tiwald’s farm but not at the concentrations Rhoads experience nor the same weeds. They also have more grass problems than Rhoads.

Having these three farms, in very different soils, which different cultural practices, somewhat different crops and different cropping systems lends a real diversity of testing that gives a wider and more complete picture of what role these herbicides can and cannot serve for the organic farmer. In our opinion this diversity of testing areas is a real strength in speeding up the knowledge gained!

The third goal was to do a weed control strategy inventories on each farm and the network systems we are involved in for the purpose of exploring possible improvements to be tested, experimented and researched in subsequent years.

By performing inventories we have targeted for the 2007 growing season the following continued studies in weed control strategies:
- Doing organic herbicides cost analysis trials under real field conditions growing various crops.
- Making preliminary trails in ways to manipulate cover crops for weed suppression for application to several different crops.

In 2003 Dr. Elizabeth Maynard of Purdue University suggested to Rhoads Farm that they try some of the newly developed organic herbicides for setting up a sterile seedbed for reducing weeding time in salad green production. Over the four years since then Rhoads has used these products and LP Flaming to reduce weeding time by more than 75%. During those three years several herbicides have become available. In 2006 Green Earth Farm in IL and Cinzori’s Family Farm, all vegetable farms using organic growing methods, joined with Rhoads in doing formal trials to test the efficiency of these products. It appears to all the farmers that if used correctly in certain crops these products and techniques could significantly reduce weeding time. Exactly how much this could save the farmer is what they are planning on trying to measure in 2007 with extensive ‘in field’ crop production trials.

From our respective field days, informal talks with other farmers, other farmers listening to this discussed on conference calls, talks at conferences and other direct communication methods in the three states approximately 300 people to date have heard from us about these products and ways we are trying them out.

We have placed a short informal paper on our collective New Ag Network Website, which had over 80,000 hits, the majority of which are Ag educators who share information with their clients. In early 2007 we will place a more formal paper stating exact results from the trials on the website.

Michigan State plans on making mention of these trials in several different Ag conferences this year. In Indiana Rhoads will talk briefly about these trials at the Indiana Horticulture Congress. Rhoads will present more in depth information on these trials as part of an organic weed control video produced by Purdue University that is being made for circulation in the Land Grant University systems of three or four local states. Rhoads will be participating in a three state project to develop and train extension agents in organic farming. Another part of that project will be to hold farmer workshops for 250 farmers for the next two years. Mention of these products and trials will be made in those programs. University of Illinois’ plans are similar to Michigan State. This will reach educators and farmers.


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.