I was awarded a SARE grant in 2003 to field test the use of vinegar as an organic herbicide in commercial garlic production. My research was directed at the in-row control of weeds only. Between-row weeding was accomplished with mechanical control. Based on the USDA-Beltsville laboratory research I selected 10% acetic acid vinegar as it was shown to possess greater ability to kill weeds than the common 5% vinegar as found in supermarkets.

The results of this field trial indicate that basally applied vinegar containing 10% acetic acid is an effective organic herbicide. According to USDA-Beltsville researchers, vinegar kills plant life by producing a breakdown of the cell membrane integrity resulting in desiccation of foliar tissue. In this research vinegar controlled all broadleaf weeds in my garlic field but provided mixed control on grasses. My particular experience in 2003 with grass control may, however, have been due to the unusually cool and wet conditions we experienced throughout our spring season in upstate-New York. Weed control appeared to be more effective when temperatures exceeded 70 degrees and direct sunlight was available. This observation is additionally supported by other research. The question of the mixed grass control is intriguing and I would have liked to look at it but the addition of variables would have been inappropriate. This project has spawned new research at Cornell -Weed Science that will address the grass issue among other variables.

For optimal effect most weeds should be sprayed when in their cotyledon or seedling stage. Many weeds can be controlled even in full leaf but may regenerate from root reserves, e.g. thistles and dandelion. I found that Canada thistle can be “burned down” even as an adult plant. In many cases the thistle regrew from its root reserves. Repeated applications eventually exhausted those reserves. This alone should justify the research for those with thistle infested pastures who wish to avoid synthetic or petrochemical based herbicides. Vinegar should be treated as a non-selective herbicide and as most herbicides it is more effective on rapidly growing plants.

I divided my research field of 12 rows each containing 250 feet length into 4 equal blocks, each with a control and test plot. Among the four blocks, test and control plots were allocated so that differing soil conditions, available moisture and fertilizer through out the test field did not unduly influence the results.

In all blocks I cultivated mechanically between-rows. In the control plots I cultivated manually in-row with a collinear hoe. In the test plots I cultivated by in-row spraying with vinegar. On 2 of the test plots I sprayed on one side of the row only and on the other 2 test plots I sprayed on both sides of the same row.

My first spray application, on May 10, was applied when the garlic was at 18” height, using a drift guard to protect the garlic as much as possible. While there was damage to the lower one or two leaves in the form of tip burn it later proved to be cosmetic. The four subsequent applications seemed to have little visible effect on the the mature garlic and I removed the drift guard for the final 2 applications. All test plots demonstrated effective broadleaf control but those that were sprayed on both sides of the row were almost totally devoid of broadleaf weeds. With regard to the garlic crop, I saw no difference in plant size, maturity date, quality, yield, and bulb size between the test and control plots.

This field trial revealed a substantial saving of labor for in-row cultivation of garlic. It would require 18-20 hours to manually in-row weed half an acre. One can basally spray the same plot in 1-2 hours. This represents at least a 90% reduction in labor!

It is important to understand the equipment and technology prior to embarking on a spray program. To this end I received training and equipment recommendations from Cornell. I am convinced that without this knowledge and the selection of appropriate equipment this project would have unsuccessful. I have seen studies that indicate many if not most spraying programs suffer from inadequate equipment and applicator knowledge. Therefore the following should be studied carefully prior to starting your own program.

The goal in herbicide spraying is the uniform application of the product on the weeds. Uniform application is achieved through the use of calibrated spraying equipment and selected travel speed. Sprayer calibration is accomplished by selecting the proper combination of pressure, volume and spray pattern for the target species. As large droplets frequently bounce off leaves and small droplets drift, controlling droplet size minimizes drift, improves effectiveness of the product, and reduces waste. Droplet size is a function of pressure and nozzle flow rate. With no pressure controlling mechanism, the droplet size varies constantly with pressure changes in the sprayer and a poor result is certain along with inefficient and ineffective use of the herbicide.

Consequently it is necessary to understand and control the below three variables: To control pressure I used a device called a CFValve (Constant Flow Valve). It provides a constant flow regardless of varying input pressure. The second variable, the nozzle, provides the flow rate and pattern. The third variable, travel speed is necessary in maintaining accurate applications. Gallons per acre are a function of nozzle flow, pressure and travel speed. I used a Solo backpack sprayer with the CFValve @ 21.5 psi and a TeeJet XR11002VS nozzle. This produced a medium droplet @ 20 gallons per acre.

Five applications on a half-acre required 50 gallons of product. The purchase of a 55-gallon drum of 10% acetic acid vinegar costs $67. Thus the cost of each treatment is $13 versus 18 hours of manual labor. Shipping cost varies based on shipping distance and is not included in the equation. At conclusion of this project no soil pH changes were found.

All vinegar is produced from natural fermentation. The common white distilled vinegar I used is made from a source of corn-based ethyl alcohol. This vinegar is available in concentrations of 5-30%. A 55-gallon drum of 10% white vinegar, at the writing of this report, was $67 FOB the Fleischmann’s plant in North Rose, NY. Higher strength 20% white vinegar is $122 per drum.

In this field trial I applied product at 20 gallons per acre thus five applications on an acre would require 100 gallons of product. It would make good economic sense to purchase the 20% strength and dilute it with water 1-1, saving the expense of shipping two drums of 10% strength weighing 568 pounds each. Shipping costs must be evaluated separately as these are variables based on shipping distance.
Finally consider the potential damage done to a small percentage of plants while manually cultivating: My garlic sells at $4/lb. or $1/bulb as the bulbs average 4 oz. If one were to damage only a total of 1% of the plants on an acre during the 5 manual cultivations, rendering them un-saleable, it would represent a product loss greater.

My findings are based on my experiences with the technology selected on the recommendations of experts for my conditions and usage. Therefore, I am not recommending that one embark on a project such as this without a working knowledge of proper spraying principles and appropriate technology.

In conclusion there is the matter of whether it is actually legal to spray vinegar on crops. Any material claiming to kill weeds by default becomes an herbicide. Legal minds will need to resolve this issue. As of this writing, OMRI has informed me that vinegar is approved for use in organic production.

At the end of the season vinegar has an advantage over other herbicides in that it can be mixed with oil and water and tossed with your salad. Vinegar the incredible edible herbicide!

The full report will be available from SARE at their website sometime in the future but as of 3/31/04 was unavailable therefore I would be happy to forward the full report at your request. It is in Microsoft Word format.

Fred Forsburg is the owner of Honeyhill Farm in Livonia, New York. He can be reached at honeyhillfarm@excite.com