sign in sign up
<<
Home , Cacodylic acid

Chemical herbicides. Holmes, F.A.-Holmes Advisory Service. There are over 100 basic chemicals currently registered for use as herbicides. These chemicals differ in their: mode of action; species controlled; methods and timing of applications; formula­ tions. A very practical classification of these herbicides is based on how the chemical is used in weed control. These classifications are: contact; foliar translocated; soil applied; aquatic.

Contact herbicides. Contact herbicides are essentially "chemical mowers". They will burn down the vegetation that is present at the time of application and when moisture and tem­ perature are conducive to growth, the plants will grow. Chemicals classified as contact herbicides are: (Blazer) Rohm & Haas Ammonium sulfamate (Ammate XNI) Du Pont Betazan (Basagran) BASF (Mo down) Mobil (Brominal, Union Carbide, Buctril) Rhone Poulenc Cacodylic Acid (Rad-E-Cate) Vineland Desmedipham (Betanex) Nor-Am Dichlofop (Hoelon) American Hoescht Difenzoquat (Avenge) American Cyan am ::..J. (Pr emerge etal) Dow, FMC (Diquat, Chevron ICI Rezlone) (Aquathol) Pennwalt Oxyfluoren (Goal ) Rohm & Haas (Paraquat, Chevron ICI Gramoxone) Phenmedipham (Betanal) Nor-Am (Stam, Rohm & Haas, Rogue) Monsanto Weed Oils

Foliar applied. Foliar translocated herbicides are the "weed killers". When sprayed on the foliage of plants, they are absorbed through the leaves and stems and translocated throughout the plant and those plants that are susceptible to the herbicide used are killed. Chemicals in this classification are: Amitrole (Amizol, Union Carbide, Cytrol) American Cyanamid (Asulox) Rhone-Poulenc Barban ( Carbyne) Velsicol 2,4-D (Several) Several 2,4-DB (Butoxone) Union Carbide, Rhone-Poulenc 2,4,5-T (Several) Several Dalapon ( Dowpon) Dow (Banvel) Velsicol ( Weedone DP) Union Carbide DSMA (Several) Several Fosamine (Krenite) Du Pont

63 (Roundup) Monsanto MCPA (Several) Several MCPR (Several) Several (Several) Several (Tordon, Dow, Amdon) Union Carbide Sil vex (Kuron, Dow, Weedone) Union Carbide ( Garlon) Dow

Soil applied herbicjdes. Soil applied herbicides are the "weed preventers''· Generally, they are applied preemergence to the weeds and prevent them from becoming a problem. Some of the.soil applied herbicides are translocated from the roots throughout the plants and can result in the death of well-established plants. Soil applied herbicides must be in the root zone area to be effective in controlling weeds. Certain of these materials can be sprayed on the surface of the soil and be incorporated by subsequent rainfall or irrigation. Others must be mechanically ~ncorporated into the soil, many of them immediately after application, to be effective. These methods will be discussed later when specific uses are studied. Soil applied herbicides are: (Lasso) Monsanto Ametryne (Evik) Ciba-Geigy (Several) Several Benefin (Balan) Elanco (Betasan, Stauffer Prefar) Bromacil (Hyvar X) Du Pont Bromacil + Diuron ( Krovar I ) Du Pont Butylate (Sutan) Stauffer CDAA ( Randox) Monsanto CDEC ( Vegadex) Monsanto Chloramben (Amiben) Union Carbide Chlorpropham (Choro,IPC, PPG Furloe) Chlorsulfuron (Glean) Du Pont (Bladex) Shell Cycloate ( Ro-neet) Stauffer DCPA ( Dacthal) Diamond Shamrock Diallate (Avadex) Monsanto Dichobenil ( Casaron) Thompson-Hayward Diphenamid ( Enide) Upjohn Diuron (Several ) Several EPTC ( Eptam) Stauffer Ethalfluralin ( Sonalon) Elanco Fenac ( Fenac) Union Carbide Fluchoralin ( Basalin) BASF Fluometron (Cotoran, Ciba-Geigy, Lanex) Nor-Am (Velpar) Du Pont ( Lorox) Du Pont ( Dual ) Ciba-Geigy

64 (Lexone, Du Pont, Sencor) Mobay Molinate (Or dram) Stauffer Monoborchlorates and mixtures Napropamide (Devrinol) Stauffer Naptalam (Alanap) Uniroyal Norflurazon (Solicam) Sandoz Oryzalin (Sur flan) Elanco Oxadiazon (Ronstar) Rhone-Poulenc Oxyfluorfen (Goal) Rhom & Haas Pebulate (Tillam) Stauffer (Prowl) American Cyanamid Perfluidone (De stun) JM Co . ( disc n t 1 d ) Polyborchorates and mixtures Profluralin (Tolban) Ciba-Geigy Prometone (Pramitol) Ciba-Geigy Prometryne (Caparol) Ciba-Geigy Pronamide (Kerb) Rohm & Haas (Ramrod, Monsanto, Berton) Dow Propazine (Milogard) Ciba-Geigy Prop ham (Chem Hoe) PPG Pyrazone (Pyramin) BASF Siduron (Tupersan) Du Pont (Several) Several Sodium chlorate and mixtures TCA (Sodium TCA) Hopkins (Spike) Elanco Terbacil ( Sinbar) Du Pont Thiobencarb (Bolero) Chevron Triallate (Far-go) Monsanto ( Treflan) Elanco Vernolate (Vernam) Stauffer

i\.quatic herbicides. Aquatic herbicides are used for control of weeds in flowing irrigation and drainage ditches and water compounds. The chemicals that are currently registered for this use are: Acrolein (Aqualin) Shell Copper-ethylene ( Komeen) diamine Copper chelate Copper sulphate (Several) Ricetrine Applied biochemists Diquat Chevron Copper-triethanolamine (K-lox) Endothall (Hydrothal 191, Pennwalt Aquathol)

65 ------

Chemical classification of herbicides. A chemical class­ ification of herbicides may be helptul to understand the types of chemicals that can be and are used as herbicides. Chemical classificationsof commonly used herbicides and corresponding common names are: Inorganic herbicides AMS (Ammate) Borate (met a) (Several) Borate ( octa) ( Polybor) Borax (Several) Calcium cyanamide (Cyanamide) Copper chelate (Cutrine) Copper-ethylenediamine (Kormeen) Copper sulfate (Copper sulfate) Copper-triethanolamine (K-Lox) Sodium chlorate (Sodium chlorate) Organic herbicides Aliphatics Chlorinate acids Dalapon (Dowpon,Radapon) TCA (Sodium TCA) Organic arsenicals Cacodylic acid (Rad-E-Cate) DSMA (Several) Others Acrolein (Aqualin) Glyphosate (Roundup) Amides Chloroacetamides Alachlor (Lasso) CDAA (Randox) Metolachlor (Dual) Propachlor (Ramrod, Bexten) Others Diphenamid (Enide) Naproparnide (Devrinol) Naptalarn (Alanap) Pronamide (Kerb) Propanil (Starn) Benzoics Chlorarnben (Amiben) Dicamba (Banvel) Bipyridiliurns Diquat (Diquat, Rezlone) Paraquat (Paraquat) Carbarnates Asulam (Asulox) Barban (Carbyne) Chlorpropham (Chloro IPC) Desrnedipham (Betanex) Fosarnine (Krenite) Phenrnedipharn (Betanal) Propharn (Chern Hoe)

66 Dinitroanilines Benefin (Balan) Ethalfluralin (Sonalan) Fluchloralin (Basalin) Oryzalin (Surflan) Pendimethalin (Prowl) Profluralin (Tolban) Trifluralin (Treflan) Diphenyl ethers Acifluorfen (Blazer) Bifenox (Modown) Diclofop (Hoelon) Oxyfluorfen (Goal) Nitriles Bromoxynil (Buctril, Brominal) Dichlobenil (Casoron) Phenoxies 2,4-D (Various) 2, 4-D.B (Various) 2, 4, 5-T (Various) MCPA (Various) MCPB (Several) Dichlorprop (Several) Mecoprop (Several) Silvex (Kuron, Weedone) Thiocarbamates Butylate (Sutan) CDEC ( Vegadex) Cycloate (Ro-Neet) Diallate (Avadex) EPTC (Eptam) Molinate (Ordram) Pebulate (Tillam) Thiobencarb (Bolero, Saturn) Triallate (Far-Go, Avadex BW) Vernolate (Vernam) Triazines Ametryn (Evik) Atrazine (AAtrex) Cyanazine (Bladex) Metribuzin (Lexone, Sencor) (Pramitol) Prometryn (Caparol) Propazine (Milogard) Simazine (Princep) Terbutryn (Igran) Uracils Bromacil (Hyvar) Terbacil (Sinbar) Ureas Di uron ( Karmex ) Fenuron TCA (Urab) Fluometuron (Cotoran) Linuron (Lorox) Monuron TCA (Urox) Siduron (Tupersan) Tebuthiuron (Spike) 67 Unclassified Amitrole (Amitrol) Fluridone (Brake) Bensulide (Betasan) Hexazinone (Velpar) Bentazon (Basagran) Norflurazon (Solicam) DCPA (Dacthal) Oxadiazon (Ronstar) Difenzoquat (Avenge) Perfluidone (Destun) Dinoseb (Several) Picloram (Tordon) Endothall (Several) Pyrazon (Pyramin) Fenac (Fenac) Triclopyr (Garlon)

Formulations. Very few chemicals can be used as herbicides in their pure state. To be an effective tool in weed control, they must be formulated into a usable product. There are several types of formulations. Which formulation is used may depend on the chemical nature of the compound or it may be formulated for a specfic purpose. The basic types of formulations are: emulsions; solutions; wettable powders; granules; pellets.

F.mulsions. An emulsion is one liquid dispersed in another liquid, eacn maintaining its own properties. When oil is added to water and shaken well, it is momentarily suspended as droplets in the water. If the mixture is allowed to stand, the oil and water will separate. In the formulation of herbicide emulsions, the herb­ icide is dissolved in an oil and an emulsifying agent is added to prevent the separation. When added to water, they have ap­ proximately the same viscosity as the water and the mixture will have a "milky" appearance. To reduce the drift hazards of some of the phenoxy com­ pounds, particularly in brush control near sensitive crops, the chemists have reversed the process to produce water in oil or invert emulsion. These have a consistency of mayonnaise and specialized equipment is needed for the application.

Solu~ions. A solution is a homogenous mixture of two or more suo~tances so that each particle or droplet on the product is exactly the same as the other. Many of the salts of technical compounds used as herbicides are soluble in water. These can readily be dissolved in the amount of water that is convenient to use in application.

Wettable powders. Many herbicides, particularly the soil residua~ ~ype ma~erials are practically insoluble in water or oil. To provide a means of application of these materials, they must be finely ground and blended with conditioning and dispersing agents to form a wettable powder. Continuous agitation is needed in the spray tank to prevent settling out and the resultant improper application. When using a wettable powder herbicide in combination with an oil base herbicide, problems may arise. This can be usually alleviated by adding the oil base herbicide to the spray tank half full of water, with agitator running, while still filling the tank and one pound of powdered milk and then add the wettable powder herbicide.

68 Another form of water dispersable powder herbicides is becoming very popular recently. This is the dry flowable formulation. These are tiny granules of highly concentrated herbicide that will flow readily. They can be measured like a liquid and they present less of a dusty environment for the persons loading the spray tank.

Granules. Many of the soil residual type herbicides are formula~ed in low concentrate granules. The carriers for these granules can be an inorganic herbicide such as borates or borate-chlorate mixtures, clay, vermiculite or possibly finely ground plant parts. These formulations are to be applied directly with no further dilution. They can be applied by hand, by cyclone seeder, fertilizer spreader or by specifically manufactured equipment for accurate calibration in crop use. Granules are more expensive on a cost-per-unit active ingredient, but they have utility in certain areas: where water is scarce; where spray equipment is not available; where the cost of application exceeds the cost of the chemical (remote areas); where the herbicide might be foliar toxic to the plant, yet safe to use as a soil applied herbicide.

Pellets. This formulation is restricted to soil residual herbicides for brush control. The pellets range in size from B-B shot to the size of apricot "pits". These are designed to give a heavy concentration of chemical where it will control the brush from the root zone without complete coverage of the area. This reduced coverage alleviates the total de.nuding of the treated area.

Spray adjuvants. An adjuvant is defined as anything which aids or nelps. Any additive made to the basic chemical ingred­ ient of a herbicide can be described as an adjuvant. This discussion will not relate to any of the adjuvants used in the manufacture or formulation of herbicides. These are all controlled by the producer. There are adjuvants that can be added to the spray tank that will enhance the applications and/or the performance of the herbicide. These will be referred to as spray adjuvants. Spray adjuvants may influence wetting and coverage, spray retention, penetration and translocation, selectivity, compatibility and drift reduction, and are used with contact or foliar-applied translocated herbicides. Water is the most widely used carrier for herbicide ap­ plications. It is not always the ideal carrier, but it is economical, generally available and safe. Many plants have a "built-in" waterproofing system, such as waxy leaves or the leaves and stems are covered by many minute hairs that prevent water from reaching the plant surface. Many adjuvants can be used if breaking the surface tension of the water to give better wetting and coverage are the only requirements.

69 Spray retention is also a major function of spray adjuvants. It is important that the spray of a contact or foliar translocated herbicide remain on the plant if it is to perform properly. The right spray adjuvants can materially improve spray retention. Penetration and translocation should be considered together in a discussion of spray adjuvants. The use of the proper ad­ juvant can enhance the penetration of the herbicide into the plant. There has been no information to show that adjuvants improve translocation. Improved penetration of the herbicide into the plant should result in more herbicide in the plant and thus improved performance. Drift from herbicide applications has been the basis for much study since the introduction of the phenoxy herbicides in the late 1940's. Drift reduction should be an important con­ sideration when making any herbicide application. Airplane and high pressure spraying generally create more controversy over spray drift than other means of application, but drift does occur in all applications. Drift cannot be completely eliminated, but there are adjuvants that can materially reduce drift. There are certain herbicides, however, whose performances, are materially altered with the most commonly used visco-elastic drift reduction adjuvants. The invert emulsions are also used to reduce drift of certain herbicides. Compatibility is a problem in many cases where combinations of herbicides are to be used. There are instances where the incompatibility can be overcome by the use of the proper ad­ juvant. There is a growing demand for the application of herbicides and liquid fertilizers in combination to save energy, application costs and compaction from so many trips across the field. Many of these mixtures may be incompatible without the use of the proper adjuvant. The use of adjuvants can enhance the herbicidal activity of many selective herbicides. Care must be taken that the adjuvant used does not alter the selectivity to the point that crop damage occurs. Great care should be exercised in the selection of an adjuvant to be used with selective herbi­ cides in crops. Adjuvants must be registered for use and must comply with FDA and EPA requirements. Adjuvants can be very useful in enhancing herbicide per­ formance, but a keen understanding of what they will do is necessary for satisfactory results.

Herbicide use and the environment. The use of any effective herbicide will have its impac~ 011 ~ne environment. The purpose for which it is used is to reduce the growth of plants that are undesirable to the user of the herbicide and to either increase the growth of desirable plants or to achieve an environment that is free from plant growth. Most herbicides are effective against several species of plants and their proper use is very essential to minimize any adverse effect on the environment which might occur.

70 Herbicides, generally, are not applied to target species but to target areas for the control of several species. These target areas include most land that has any economic value. Herbicides are used for weed control in cropland, roadside streets, lawns, rights-of-way, forests, irrigation and drainage ditches, home gardens, and watershed areas. The broad spectrum of use of herbicides in vegetation management offers many possibilities for "misuse and abuse" of chemicals that can create environmental problems. Because of the broad spectrum of use and the potential hazard to many adjacent desirable plants, it is highly de­ sirable that herbicides be applied by well-trained applicators. There have been many allegations to the effect that the use of herbicides have had deleterious effect on animal life. To date, none of these have been substantiated. There have been some reported alterations of the animal populations due to the planned elimination of certain weed species. Certain bird populations may be reduced by reducing their food supply or nesting areas. Root feeding animals, such as gophers, may be affected by a reduction of food supply. We have observed the reduction of midge populations in drainage ditches when their breeding places and food supply have been eliminated by the use of herbicides. Mosquito control is enhanced either chemically, biologically, or mechanically if their breeding areas are maintained free of undersirable vegetation. Cropland applications of herbicides have little or no impact on the environment. The undesirable vegetation in these areas is generally controlled by some means, so their removal by chemicals creates no problem. The use of herbicides as an effective tool to alter the environment for the greatest benefit for all concerned, flora and fauna, offers a great challenge, but the proper people, proper programs, and proper products, properly used will accomplish the project. (Holmes Advisory Service, 118 Blueberry Hill, Los Gatos, CA 95030).

References. "Adjuvants-Their influence on herbicides" 30th Annual Proceedings, CWC, p 119.

"Agricultural chemicals" Book II, Herbicides W. T. Thomson.

"Report on environmental assessment of pesticide regulatory programs", State Component, Volume II, 1978.

WSSA "Handbook of herbicides".

71