Organic Production and Marketing Newsletter
 January 2005

Status and Preliminary Research on Non-Synthetic Herbicides for Organic Production

Organic growers have consistently ranked weed management as one of their most important production problems and have used a variety of methods including flaming, hot water treatments, solarization, cultivation, mowing, mulching, and cover crops to control weeds. Non-synthetic herbicides may also be used in organic production. However, these non-synthetic herbicides are restricted (must be approved by the grower's organic certifying agency), suggesting that other cultural practices like cover crops and mowing be used first.

Procedures for identifying and registering non-synthetic herbicides for possible use in organic production are complex, involving federal and state laws and regulations as well as national and local organic certifying agencies. Our purpose is to explain this process and to review preliminary research on several non-synthetic herbicides.

The Organic Materials Review Institute

The National Organic Program establishes general standards for certification procedures and inputs that are used in organic farming and processing but does not maintain a list of trade name products. The Organic Materials Review Institute (OMRI), a non-profit organization, fulfills this function, charging “certifiers, growers, manufacturers, and suppliers for an independent review of products intended for use in certified organic production, handling, and processing under the USDA National Organic Program standards.” OMRI approval is an ongoing process. That is, products may be added or deleted, depending on continual product evaluation.

Note also that OMRI reviews products in terms of their ingredients but not in terms of their effectiveness or federal and state registration. Furthermore, products listed by OMRI, like herbicides, must also be approved by the local organic certifying agency if such products are restricted. Another option for pesticide manufacturers to market their products to organic growers is to ensure that the ingredients of their products conform to national organic standards, without going through the OMRI, fee-based approval process.

Minimum Risk Pesticides

All pesticides (including herbicides), be they conventional pesticides or those listed by the Organic Materials Review Institute for use in organic farming, must either be registered by the Environmental Protection Agency (EPA) or be exempted from registration. The federal law governing pesticide registration is The Federal Insecticide and Rodenticide Act (FIFRA). Under section 25 (b) of FIFRA, “minimum risk” pesticides are exempted from EPA registration because such pesticides contain compounds that are classified as Generally Regarded as Safe (GRAS) and can be used on food crops without the pesticide label listing all possible crop uses.

Another important distinction for pesticide registration or exemption is made between “active” and “inert” pesticide ingredients. An active ingredient is intended to kill, poison, or repel a pest whereas an inert ingredient, listed separately, is not intended to affect a target pest. Active ingredients must be listed by name and percentage (by weight). All other (inert) ingredients must be listed by name but not necessarily listed separately by percentage weight. Tables 1 and 2, respectively, contain the current list of allowed active and inert ingredients of minimum risk pesticides under Section 25 (b) of FIFRA.

For example, the product label for Matran 2, an herbicide listed by OMRI, contains the statement: “This product has not been registered by the US Environmental Protection Agency. Biorganic® represents that this product qualifies for exemption from registration under the Federal Insecticide, Fungicide, and Rodenticide Act.” The active ingredient for Matran 2 is Clove Oil (45.8%), found in Table 1 with “Other Ingredients” or inerts listed as “Water, Lecithin: 54.4%," found in Table 2.

Another more controversial example is acetic acid or vinegar. Acetic acid has been used by researchers at relatively high concentrations (about 20%) to control weeds and could presumably be used to manage weeds in organic farming systems. But the classification of acetic acid as an inert or secondary ingredient (Table 2), rather than as an active or primary ingredient, in herbicides (Table 1) has prevented its registration as an herbicide in some states like Florida. If a company developed an herbicide with acetic acid as an active ingredient, tolerances for food crops for this compound would have to be established - a costly process. Two acetic acid herbicide formulations are registered in Florida: Natures Glory Weed and Grass Killer® a 6.25% ready-to-use concentration and a 25% concentration requiring dilution. Both formulations are registered in Florida for use on ornamental plants and turf, farm yards, rights of way, etc. for a range of grass and broadleaf weeds but not for food crops, because as mentioned above, tolerances have not been established. However, inert ingredients can be included in minimum risk herbicides at high enough concentrations to have an herbicidal effect. This is exactly what has happened, with some manufacturers directly or indirectly claiming herbicidal properties for materials containing an undefined concentration of acetic acid.

 State Regulation of Minimum Risk Herbicides

A product fulfilling FIFRA requirements as a minimum risk herbicide and listed by OMRI may not be exempt from state registration or other regulatory requirements. The Florida Department of Agriculture and Consumer Services (FDACS), Division of Agricultural Environmental Services, and the Bureau of Pesticides (http://www.flpesticide.us/) maintain an on-line Florida Registration Tracking System that lists pesticides registered in Florida as a minimum risk pesticide according to section 25 (b) of FIFRA. For example, non-synthetic herbicides like Matran 2 and Xpress are listed by OMRI (http://www.omri.org/crops_generic.pdf) and are found in the FDACS Registration Tracking System but other non-synthetic herbicides may not be so listed.

OMRI had listed Alldown®, Matran 2®, and Xpress® as all contact or burn down herbicides. However, as of 10/25/04, only Matran 2 and Xpress were listed on the OMRI product web site (http://www.omri.org/crops_alpha.pdf) (Table 3). Alldown is mentioned here because it was OMRI approved when the research described below was conducted. The active ingredients of Matran 2 and Xpress are essential oils (the oil obtained after extracting highly aromatic cells from a plant by distillation), with Matran 2 containing clove oil and Xpress containing both clove and thyme oil plus acetic acid and other ingredients. Both clove oil and thyme oil contain phytotoxic compounds and have been reported to kill johnsongrass, common lambsquarters, and other grasses and broad leaf weeds. Xpress contains acetic acid but as an inert ingredient at an undefined concentration (Table 3). Alldown, another non-synthetic herbicide, also contains acetic acid. However, acetic acid is not listed as an active ingredient allowed in minimum risk herbicides (Table 1). Therefore acetic acid cannot be registered as an herbicide and cannot be recommended for weed control for food crops by Extension faculty. Such recommendations are based on several years of field research, usually funded by the pesticide manufacturer. Unfortunately, many small companies producing pesticides and other materials for possible use in organic production do not have the financial resources to fund such research.

Alldown, Matran 2, and Xpress have been applied to grasses and broadleaf weeds in Kentucky and Florida (Table 4). Alldown applied at high rates (40 to 70 gallons per acre) killed from 82 to 100% of Kentucky bluegrass turf in that state within 24 hours but within five weeks all the turf recovered, compared with 7% recovery of turf treated with Roundup®. More variable results were reported from Florida, with Alldown, at 40 gallons per acre providing inconsistent control of grasses and broadleaf weeds in one trial but in another experiment (rate per acre not specified) providing 70% control within one week, declining to 60% in three weeks. Both tests were conducted on former pasture land as a weed control trial with no host crop. Note also that Alldown was applied at full product concentration. Further testing is being conducted this year.

In Florida, Matran 2 provided 70% control in one case, declining to less than 60% within three weeks. However, when weeds were tilled before herbicide application, Matran 2 provided up to 75% control within five weeks. In both Florida trials Xpress did not provide uniform weed control.

USDA researchers have also used acetic acid to control weeds but at higher concentrations (up to 20%) than are found in food-use acetic acid or vinegar (3-5%). When acetic acid was applied at about 6 to 13% concentrations as a directed spray or broadcast at different times, broadleaf weeds were suppressed during the potato growing season in West Virginia but nutsedge and other grasses were only temporarily controlled. In sweet pepper fields, higher concentrations of acetic acid (18%) provided better control but only for about a month. Using 5 to 20% acetic acid concentrations as basal and foliar sprays on corn and soybeans, early-season sprays afforded greater control of younger weeds than later, seasonal sprays but at the cost of some crop damage (Table 4).

USDA researchers also advise that due to the corrosive nature of acetic acid, spray equipment should be taken apart and individual components such as O rings should be rinsed well after using herbicides containing acetic acid. Note also that acetic acid concentrations over 11% can cause burns upon skin contact.

Summary

Active and inert ingredients allowed in minimum risk herbicides are clearly defined under federal laws but the percent composition of inert ingredients is not clearly defined, allowing for inclusion of compounds with some herbicidal effect. Two non-synthetic herbicides listed by OMRI are also registered for use in Florida but preliminary research has indicated varying efficacy. Acetic acid has been used as an herbicide in experimental trials but is not now registered as the active ingredient in an herbicide because of lack of data on tolerances in food crops.
 

Table 1.  Active Ingredients Which May Be in Minimum Risk Pesticide Products Exempted under section 25(b) of FIFRA.  Appendix A PR Notice 2000-6

1. Castor Oil (U.S.P. or equivalent)

17. Linseed Oil

2. Cedar Oil

18. Malic Acid*

3. Cinnamon* and Cinnamon Oil *

19. Mint* and Mint Oil*

4. Citric Acid*

20. Peppermint* and Peppermint Oil*

5. Citronella and Citronella Oil

21. 2-Phenethyl Propionate (2-phenylethyl propionate)

6. Cloves* and Clove Oil*

22. Potassium Sorbate

7. Corn Gluten Meal*

23. Putrescent Whole Egg Solids (See 180.1071)

8. Corn Oil*

24. Rosemary * and Rosemary Oil*

9. Cottonseed Oil*

25. Sesame* (includes ground Sesame plant stalks) (See 180.1087) and Sesame Oil*

10. Dried Blood

26. Sodium Chloride (common salt)*

11. Eugenol

27. Sodium Lauryl Sulfate

12. Garlic* and Garlic Oil*

28. Soybean Oil

13. Geraniol

29. Thyme* and Thyme Oil*

14. Geranium Oil

30. White Pepper*

15. Lauryl Sulfate

31. Zinc Metal Strips (consisting solely of zinc metal and impurities)

16. Lemon grass Oil*

 

* These active ingredients are exempt for use on all food commodities from the requirement of a tolerance on all raw agricultural commodities at 40 CFR 180.1164(d).

 

Table 2.  Appendix B PR Notice 2000-6. LIST 4A Minimal Risk Inerts. Parentheses indicate exemption from tolerance as inerts if all the conditions set forth in the text and tables shown for the particular substance at 40 CFR 180.1001(c), (d) and/or (e) are met.

Acetic acid (c, d, e)     

Carrots            

Agar                

Casein (c)

Alfalfa

Cheese

Alfalfa meal

Chlorophyll

Almond hulls

Cinnamon (d)

Almond shells (c)

Citric acid (c, e)

Alpha cellulose (c)

Citrus meal (c)

Apple pomace (c)

Citrus pectin

Attapulgite-type clay (c, e)

Citrus pulp

Beef fat

Clam shells

Beeswax (c)

Cloves (d)

Beet powder

Cocoa

Bentonite (c)

Cocoa shells (c)

Bicarbonate (c)

Cocoa shell flour

Bone Meal

Cod liver oil (c)

Bran

Coffee grounds (c)

Bread crumbs

Cookies

Calcareous shale (c)

Cork

Carbon dioxide

Corn (d)

Calcite (c)

Corn cobs (c)

Calciumcarbonate (c,e)

Corn flour

Canary seed

Corn meal (c)

Cane syrup      

Corn oil (c)

Cardboard

Cornstarch (c)

Carrageenan (c, d, e)

Hearts of corn flour

Corn syrup (c, e)

Hydrogenated vegetable oils

Cotton

Honey

Cottonseed meal

Invert sugar (c)

Cottonseed oil (c)

Invert syrup (c)

Cracked oats

Kaolinite-type clay (c, e)

Cracked wheat

Lactose (c)

Dextrin (c, e)

Lanolin (d)

Dextrose (c, e)

Lard (c)

Dolomite (c)

Latex

Douglas-fir bark, ground (d)

Lecithin (c)

Egg Shells

Lime

Eggs

Limestone

Edible fish meal (c)

Linseed oil

Edible fish oil (c)

Malt flavor

Flour (wheat, d)

Meat meal

Fuller's earth

Meal scraps

Gelatin

Medicated feed

Glue, as depolymerized animal collagen

Mica (c)

Glycerin (glycerol; c, d, e)

Milk

Granite (c)       

Millet seed

Graphite (c, d, e)

Mineral oil, U.S.P. (c, e)

Ground oats

Molasses (c)

Guar gum (c)

Montmorillonite-type clay (c, e)

Gum arabic (c)

Nitrogen

Gum tragacanth

Sawdust

Gypsum (c)

Seaweed

Nutria meat

Shale

Nylon

Soapstone (c, e)

Oatmeal (c)

Sodium (c)

Oats (c)

Sodium chloride (c)

Olive oil

Sorbitol (c, e)

Onions

Soybean hulls

Orange pulp (as pomace c)

Soybean meal              

Oyster shells

Soybean oil (c, e)

Paper (fiber; d)

Soy flour (c)

Paprika

Soy protein (c, e)

Paraffin wax

Sucrose (c, e)

Peanut butter

Sugarbeet meal

Peanut oil

Sunflower seeds

Peanuts

Tallow

Peanut shells (c)

Vanillin (d)

Peat moss

Vermiculite

Pecan shell flour

Vitamin C

Pectin

Vitamin E

Polyethylene film (c)

Walnut flour

Polyethylene pellets , edible

Walnut shells (c)

Potatoes

Water

Pumice

Wheat (d)

Raisins

Wheat germ oil

Red cedar chips

Whey

Red dog flour

Wintergreen oil (c)

Rice

Wool

Rice hulls

Xanthan gum (c, e)

Rubber

Yeast

Rye Flour

  

Safflower oil

  

180.1001 (c) = exempt for both growing crops & crops after harvest
(d) = exempt for growing crops only
(e) = exempt for animal applications only
Please Note: List 4A, "Minimal Risk Inerts" (Appendix B of this notice) is updated on a continuing basis.
Current versions are available on the Pesticides Web site at http://www.epa.gov/opprd001/inerts/inerts_list4.pdf

 

Table 3.  Herbicides approved by Organic Materials Review Institute (OMRI).

Herbicide

 

Active ingredients
(%)

Estimated cost/gallon
 ($)

Manufacturer

 

Matran-2

Clove oil:   45.6
Other (lecithin, water):   54.4

79.60

 

Encore
Technologies, Minnesota

Xpress

 

Thyme oil:  10.4
Clove oil:   10.1
Inert ingredients:   79.5
(acetic acid, molasses, water)

84.00

BiohumaNetics, Arizona

 

Table 4. Weed control with OMRI-approved herbicides (Matran 2 and Xpress) Alldown and acetic acid. 

Location
(Date)

Crops

Treatments

Results

Authors

Florida
(2004)

pasture        

Three nonsynthetic, postemergence, contact herbicides (Alldown, Matran 2 and Xpress) and corn gluten meal applied preemergence and flaming, applied after a mowing or tillage pretreatment or with no pretreatment                       

With no pretreatment or with mowing as a pretreatment, flaming provided 97% weed control after 1 week, declining to 79% after 3 weeks.  Alldown (undiluted) and Matran 2 (20%) provided 70% control within 1 week, but control declined to less than 60% by 3 weeks.  With tillage as a pretreatment, corn gluten meal, Matran 2 (20%), and flaming provided 68-75% control within 5 weeks. Xpress gave inconsistent results.

Chase, C.A., J.M. Scholberg, and G.E. MacDonald.  2004.  Preliminary evaluation of nonsynthetic herbicides for weed management in organic orange production.  Proc. Fla. State Hort Soc. In press.

Florida
(2004)

 pasture

Three nonsynthetic, postemergence, contact herbicides plus an adjuvant (Alldown, Matran 2 and Xpress) compared with glyphosate (Roundup Pro).

Alldown (100% concentration at 40 gallons per acre), Matran 2 (10% at 5 gallons per acre), Xpress (7.5-15%) at 7.5-15 gallons per acre provided inconsistent weed control compared with glyphosate (5% Roundup Pro).

Ferguson, J.J. 2004.  Evaluation of organic herbicides.  HortScience. 39: 876. Abstract.

Iowa
(1999)

Kentucky bluegrass

Alldown at 10, 20, 30, 40, 50, 60, and 70 gallons per acre compared with Roundup (label rate) and an untreated control.

10 to 40 gallons per acre killed from 13 to 73% of turf within 24 hours but within one week, from 93 to 57% turf had recovered, respectively.

40 to 70 gallons per acre killed from 82 to 100 % of turf within 24 hours but within 5 weeks 100% of  turf recovered compared with 7% treated with Roundup.

Bingaman, B.R. M.J. Howieson, and N.E. Christians. 1999. Alldown natural herbicide study.  http://turfgrass.hort.iastate.edu/pubs/

turfrpt/2000/alldown.html

West Virginia
(2003)

Potatoes

Vinegar (Acetic Acid: 6.25 or 12.5%) as directed spray or broadcast early, late, or early + late.

Broadleaf plaintain and yellow wood sorrel counts lower in vinegar-treated plots than in nontreated plots during the growing season. Yellow nutsedge and orchardgrass were suppressed for two to three weeks but regrew later. 

USDA: Chandran, R.S., M. Stenger, and M. Mandal. Abstract. Effect of vinegar on potato weed control.  Northeastern Weed Science Society.

West Virginia
(2002)

Sweet peppers

Vinegar (acetic acid: 4.5, 9.0, and 18%); corn gluten (20, 40, and 80 lbs/1000ft2)

Directed application of vinegar (4.5, 9.0, and 18%) provided >90% control of carpetweed, Canada thistle, yellow wood sorrel, common purslane, common lambsquarters, smooth pigweed, and velvet leaf and 50% control of yellow nutsedge when applied at 18% concentration. However, 1 month after treatment,  only 20 to 30% weed control was obtained compared with untreated plots.

Corn gluten applied at 80 lbs/1000 ft2 reduced weed counts 78% three weeks after treatment and 32% 2 months after treatment

Chandran, R.S. Evaluation of vinegar and corn gluten for weed control in field-grown sweet pepper. Northeastern Weed Science Society.
  Corn, soybeans

Vinegar (acetic acid at 10 and 20%) sprayed (early treatment) to base of corn planted in rows (40 days old) and soybeans (55, 61, and 80 days old)

Vinegar (acetic acid at 10 and 20%) sprayed (late  treatment) to base of corn (55 days old) and soybeans (68, 74, and 93 days old)

Vinegar (acetic acid at 10 and 20%) foliar and basal spray in replicated plots

Vinegar (acetic acid at 10 and 20%) sprayed at 30, 60, and 90 gallons/acre

5-35% corn injury.

Giant foxtail control ranged from 100 (early spray) to 55% with late spray. Pigweed control ranged from ranged from 99% (early spray) to 55% (late spray).
5 to 45% soybean damage, especially on younger plants. 

More corn damage with foliar spray at 20% concentration

20% acetic acid at 90 gallons per acre did not control weeds > 50 days old

 Radhakrishnan, J., J.R. Teasdale, and C.B. Coffman.  Agricultural applications of vinegar.  Northeastern Weed Science Society.
2001  

0.0, 5.0, 10.0, 15.0, and 20.0 % vinegar sprayed on common lambsquarters, giant foxtail, velvetleaf, and smooth pigweed (22, 29, and 35 day-old plants) and Canada thistle (30, 40, and 50 days old)

Weed foliage in greenhouse experiments

 5 and 10.0 % concentrations more effective on younger weeds but 15 and 20% more effective on older weeds. 15 and 20% concentrations killed 90-100 % of all weeds. 5% concentration provided 100% top kill of Canada thistle with some root regrowth RadhakrishnaK. J., J. R. Teasdale, and C. B. Coffman.  Vinegar as a potential herbicide for organic agriculture. Northeastern Weed Science Society

Matran 2 and Xpress are listed by the Organic Materials Review Institute (OMRI).  Alldown was listed as of 10/25/04 (http://www.omri.org/crops_alpha.pdf).

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