ISSUE 12 July 18, 2002
USE OF VINEGAR AS A HERBICIDE
Some home gardeners already use vinegar as a herbicide, and some garden stores sell vinegar pesticides. But no one has tested it scientifically until now.
Agricultural Research Service scientists offer the first scientific evidence that it may be a potent weedkiller that is inexpensive and environmentally safe--perfect for organic farmers. ARS is the U.S. Department of Agriculture's chief scientific research agency.
ARS researchers Jay Radhakrishnan, John R. Teasdale and Ben Coffman in Beltsville, Md., tested vinegar on major weeds--common lamb's-quarters, giant foxtail, velvetleaf, smooth pigweed and Canada thistle--in greenhouse and field studies.
They hand-sprayed the weeds with various solutions of vinegar, uniformly coating the leaves. The researchers found that 5- and 10-percent concentrations killed the weeds during their first two weeks of life.
Older plants required higher concentrations of vinegar to kill them. At the higher concentrations, vinegar had an 85- to 100-percent kill rate at all growth stages. A bottle of household vinegar is about a 5-percent concentration.
Canada thistle, one of the most tenacious weeds in the world, proved the most susceptible; the 5% concentration had a 100% kill rate of the perennial's top growth. The 20% concentration can do this in about 2 hours.
Spot spraying of cornfields with 20% vinegar killed 80 to 100% of weeds without harming the corn, but the scientists stress the need for more research. If the vinegar were sprayed over an entire field, it would cost about $65 per acre. If applied to local weed infestations only, such as may occur in the crop row after cultivation, it may only cost about $20 to $30.
The researchers use only vinegar made from fruits or grains, to conform to organic farming standards. A Yankton, SD grower has been using vinegar for 3 years. He buys 55-gallon drum at $300 a barrel and applies on average about 5 gallons of vinegar/A. Some reports claim spot treatments in corn fields with a 20% vinegar concentration controlled 80% to 100% of the weeds (specific weeds not mentioned) without harming the corn.
Dr. Kirk Howatt, NDSU weed scientist initiated applied vinegar in field conditions earlier this summer to evaluate weed control from vinegar. He used vinegar from a grocery store (5% acetic acid) and sprayed the undiluted liquid at 10 gpa, at 8:30 am to small foxtail, wheat, corn, millet, smartweed, pigweed, sugarbeets and a few kochia and common lambquarters. No visible effects were seen within the first two weeks after spraying. In a separate application, Dr Howatt applied a vinegar solution to barnyardgrass, common mallow, common ragweed, and Canada thistle. Inspection the following day found no evidence of herbicide symptoms or activity on any weeds sprayed.
MORE ON VINEGAR AS A HERBICIDE
A number of questions have been raised about use of vinegar as a herbicide. Michael D. K. Owen, Extension weed management specialist with Iowa State University, contacted the USDA researchers that conducted the work and also checked a number of sites on the Web for information. The information below is from discussions with the researchers Dr. John Teasdale and Dr. Jay Radhakrishnan, and publicist Don Comis, and is reported at several Web sites:
It is important to recognize that the use of acetic acid (vinegar), unless the material is specifically labeled as a herbicide, is illegal and a violation of FIFRA. A number of companies have registrations for acetic acid to be used as a herbicide.
This information can be accessed at:
http://www.bradfieldind.com , and
Various lawn and garden stores may carry these products. Like any herbicide, it is important to follow all directions and safety procedures. The USDA issued a warning in their research report stating; "WARNING: Note that vinegar with acetic acid concentrations greater than 5 percent may be hazardous and should be handled with appropriate precautions." However, acetic acid is not reported to accumulate in the environment and readily breaks down to water. Interestingly, 24 percent acetic acid apparently can temporarily decrease soil pH. Acetic acid is not a selective herbicide. Dr. John Teasdale suggested the mechanism of action of acetic acid is similar to that of paraquat in that acetic acid causes the rapid dissolution of cell membrane integrity resulting in the dessication of foliar tissues, and ultimately plant death. Acetic acid is non-selective, and may damage any plant part contacted by the material. The USDA researchers suggested the spot spraying at the base of corn might be the most effective manner to utilize acetic acid as a herbicide. Broadcast applications of 20 percent and 30 percent acetic acid solutions would cost approximately $66 to $99 per acre, respectively. Banded applications could reduce that cost to one third of the broadcast rate.
SOYBEAN LEAF CUPPING: WHAT ARE THE CAUSES?
Reports across the state mention cupped soybean leaves and a number of the symptoms are described.
Some of the possible causes are:
1. Somehow the soybeans have been exposed to a growth-regulator herbicide used for weed control in corn.
a. Residues remaining in/on the spray equipment from previous applications in cornfields are detached and applied with the soybean herbicide at low concentrations.
b. Herbicide vapors on the plant or soil surface move out of the treated area and are absorbed by soybeans (vapor drift).
c. Physical drift of spray particles during the actual application process.
2. The soybean plant is expressing a physiological
response to adverse growing conditions
3. The response is induced by a postemergence soybean herbicide application.
The available literature tends to suggest that this type of injury does not always necessarily result in soybean yield loss, but several factors are involved in determining if yield loss will occur. In particular, soybean variety, time of exposure, and dosage are important factors that determine if yield loss will or will not occur.
NDSU Extension Weed Specialist