Alternatives to Glyphosate © 2018 Bio-Integral Resource Center
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VOLUME XXXII, NUMBER 1-4, SPECIAL ISSUE (PUBLISHED DECEMBER 2018) Drawing courtesy Diane Kuhn Alternatives to Glyphosate © 2018 Bio-Integral Resource Center. All rights reserved. ISSN 8756-7881 Common Sense Pest Control XXXII(1-4) Special Issue 2018 2 Box 7414, Berkeley, CA 94707 Least-Toxic Photo courtesy Pharm Solutions Herbicides By William Quarles About 280 million pounds of glyphosate are applied each year, nearly a pound for each person in the U.S. Much of it is applied to genetically modified crops, but it is also used for weed control in urban and subur- ban landscapes, home lawns, golf courses, and schools (USGS 2015; Duke and Powles 2009). Amounts applied have increased five-fold since 1998, causing the EPA to increase residues allowed on food items such as soybeans. Systemic glyphosate cannot be Concentrated vinegar is corrosive, and personal washed off, and residues cannot be destroyed by cooking protection must be used. Residuals degrade quickly (Kruger et al. 2014; EFSA 2009). There is widespread to carbon dioxide and water. contamination of breakfast cereal, wine, and other com- modities. Glyphosate has been found in the bodies of 93% of people tested in the U.S. (Detox 2016). A study of Least-Toxic Herbicides senior citizens showed urinary concentrations of gly- Herbicides are either pre-emergent or post-emergent. phosate increased about 6-fold between 1999 and 2016 Corn gluten meal is the only pre-emergent least-toxic (Mills et al. 2017). herbicide (Quarles 1999; Quarles 2001). Post-emergent According to the International Agency for Research on products currently available are broad-spectrum contact Cancer (IARC), glyphosate is a probable human carcin- herbicides that kill weeds by desiccation or oxidation. ogen, and thousands of lawsuits have been filed against The products are mostly soaps, fatty acids, essential oils, Bayer and Monsanto (Guyton et al. 2015; NYT 2018). or mixtures of these. Results are immediate and dra- The EPA safety threshold of 1750 parts-per-billion (ppb) matic. They will kill foliage, but not root systems. Initial for human exposures in the U.S. may not protect the effectiveness can approach 100%, but foliage grows back. population. European standards are 500 ppb for the These herbicides should be evaluated after four weeks to general population and 100 ppb for pest control opera- see if reapplication is needed. They are best for broadleaf tors (Quarles 2017a). Glyphosate formulations such as annuals, and are more effective with repeated applica- Roundup® are considerably more toxic than glyphosate tion, and good plant coverage (Smith-Fiola and Gill 2017; (Defarge et al. 2018). Applicators are most at risk, and a Wilen and Neal 2016). jury trial in California resulted in a $289 million dollar Important variables are concentration and cover- award to a landscape professional dying of non-Hodgkins age volume. Effectiveness increases with concentration lymphoma (NYT 2018). and the number of gallons per acre of solution applied. IPM Methods For instance, 15% vinegar applied at 68 gal/acre gives about the same results as 30% vinegar applied at 34 gal/ Glyphosate alternatives in GMO crops are needed be- acre (Evans et al. 2009). Since these herbicides work by cause of weed resistance (Culpepper 2006). But stacked desiccation, sunny days, higher humidity, and warm- trait alternatives using herbicides such as dicamba have er temperatures can be helpful (Brainard et al. 2013). developed their own problems, such as crop damage from Least-toxic herbicides have low residual toxicity to mam- herbicide drift (Quarles 2017b). Alternatives are also mals and the environment. But substances such as con- needed for roadside weed control, for municipal land- centrated vinegar (acetic acid) are corrosive and must be scapes, for golf courses, playing fields, and weed control handled with care. If consumers have sensitivity to odors in home lawns and gardens. Cities are especially con- of clove, oranges, or vinegar, fatty acid or soap herbicides cerned about potential liability and are actively seeking might be the best choice (Quarles 2010). alternatives (NYT 2018). Upfront costs of least-toxic herbicides are greater than IPM methods can provide a comprehensive solution those of glyphosate. But glyphosate costs are under- to weed management. These include weed mapping, estimated. Upfront costs do not include environmental cultural controls, mulching, microbials, mechanical damage such as destruction of monarch butterfly hab- controls, steaming, flaming, solarization, allelopathy, itat, disruption of soil ecology requiring more fertilizer and application of least-toxic herbicides (Quarles 2001; applications, or the payment of expensive lawsuits (NYT Quarles 2003). The IPM approach is reviewed in the 2018; Hartzler 2010; Pleasants and Oberhauser 2012; second article in this issue. This article will emphasize Quarles 2017b). least-toxic herbicides. Common Sense Pest Control XXXII(1-4) Special Issue 2018 3 Box 7414, Berkeley, CA 94707 Corn Gluten Meal treatment on organic farms and on lawns (Lewis 2011; OMRI 2018). Good results with corn gluten Acetic acid shows little potential meal require skill and patience. for bioaccumulation and easily You cannot apply it too early, you biodegrades to carbon dioxide and cannot apply it too late. Best results water. It could be used to control follow applications 3-5 weeks before unwanted vegetation along roadsides weed germination. Application rates 2 and range lands; for control of weeds are about 40 lbs/1000ft (Quarles by homeowners around yards, brick 1999; Christians 1995). Some of the walls and patios; for weed control in weed suppression may be due to cracks in pavements (USDA 2002). the fertilizer effect on turfgrass, so The acetic acid in vinegar there is an interaction between weed can kill several important weed cover and the kind of turfgrass. In species. Vinegar from the grocery stands of Kentucky bluegrass, Poa store contains 5% acetic acid. pratensis, weeds such as crabgrass, More concentrated solutions dandelion, and clover see 90% are more effective weed killers. reduction. Better results have been USDA researchers have shown seen in lawns rather than in weed that water containing 10, 15 or suppression along roadsides. Corn 20% acetic acid killed 80-100% gluten meal is pre-emergent and of annual weeds tested, including Least-toxic herbicides are effective has no post emergent effects (Barker giant foxtail, Setaria faberi; up to for broadleaf weeds such as and Prostak 2014). three inches in height, common lambsquarters, C. album. Abouziena et al. (2009) found that lambsquarters, Chenopodium album; corn gluten meal suppressed a num- up to five inches, smooth pigweed, ber of persistent weeds in greenhouse By 72 hrs weed control was 95- Amaranthus hybridus; up to six 100%. Good weed control (>80%) was tests. At four weeks after treatment, inches, and velvetleaf, Abutilon stranglervine was 55% controlled, seen for 5 weeks with one application theophrasti; up to nine inches of the concentrated (20% acetic acid) wild mustard 99%, black nightshade (USDA 2002). 92%, sicklepod 97%, velvetleaf 87%, products. Control with vinegar (5%) For its tests, the USDA used a only lasted two weeks. Effects of and redroot pigweed 72%. Efficacy in commercially supplied white vinegar potting soil was greater than in sandy concentrated acetic acid were more distilled from grain, with acetic acid persistent than with Scythe™ (see soil for wild mustard, annual rye- concentrations ranging from 5-30%. grass and goosegrass. below), which showed about 60% They also made use of an apple control after five weeks. The products vinegar at concentrations up to 14% were very effective for crabgrass, acetic acid. Acetic acid should be broadleaf plantain, and ground ivy. handled carefully, as concentrated When 30% acetic acid was applied solutions could burn the skin or to a number of early stage broadleaf eyes. It has very strong “vinegary” and narrowleaf weeds in greenhouse smell, but when used outside the tests, control was excellent (95-100%) smell dissipates quickly (USDA at four weeks after treatment except 2002; Quarles 2002). Ordinary 5% household vinegar is effective only for very small weeds, 3-5 inches or so in height. But products containing 20% acetic acid can be effective for larger weeds. A field test in Oklahoma showed that acetic acid was more effective for broadleaf weeds than grasses. Broadleaf control was about 84%. Overall weed control including crabgrass ranged from 44 to 63%. Control increased with concentration Corn gluten meal can suppress and spray volume, and 100 gal/ dandelions in turfgrass. acre was optimal. Adjuvants such as canola oil had little added effect (Webber et al. 2005). Vinegar Chinery and Weston (2001) tested Vinegar (acetic acid) is an acetic acid at several concentrations herbicide with low environmental on small turf plots in New York. impacts. It is registered for spot Weeds were quackgrass, crabgrass, ground ivy, dandelion, and plantain. Vinegar or fatty acids can control crabgrass, Digitaria spp. Common Sense Pest Control XXXII(1-4) Special Issue 2018 4 Box 7414, Berkeley, CA 94707 for sicklepod (62%), crowfootgrass the bud stage (0.3-0.9 m) reduced (25%), and yellow nutsedge (58%) weed cover by 88%. Mowing plus (Abouziena et al. 2009). Suppress reduced weed cover by 95%(DiTomaso et al. 2017). Fatty Acids Fatty acids can kill weeds by Soap desiccation. When fatty acids ranging from two carbons to ten were tested, Various soaps have been used as least-toxic postemergent herbicides. the best for desiccation of beans These materials are relatively benign, before harvest were C8 (caprylic acid), and in fact, soaps are salts of fatty and C9 (pelargonic acid or nonanoic acids. Herbicidal soaps work best acid). Capric acid (C10) also had on annual weeds, since they only high effectiveness. Emulsifiers and destroy exposed foliage. They do not adjuvants increased effectiveness of translocate to kill perennial roots, but the acids (Coleman and Penner 2006). will kill perennial foliage.