THESIS . “MW LIBEA 331' hfichia an State University rim—m: E This is to certify that the I thesis entitled .1 EFFICACY OF GLYPHOSATE (N-PHOSPHONOMETHYL GLYCINE) $1 5 'IN SELECTIVE TOPICAL APPLICATION FOR ‘ HORTICULTURAL CROPPING SYSTEMS presented by Helen Anita Retzner has been accepted towards fulfillment of the requirements for Master of Science deg-gem Horticulture ///’I [1 ’/,/ J7/é/eKL (7%! 114141. Major professor I. 'f( '7r, Date \jLu I I )1" f” K 0-7639 OVERDUE FINES: 25¢ per day per its: RETURNING LIBRARY MATERIALS: Place in book return to remove charge from circulation records EFFICACY OF GLYPHOSATE (N-PHOSPHONOMETHYL GLYCINE) IN SELECTIVE TOPICAL APPLICATION FOR HORTICULTURAL CROPPING SYSTEMS By‘ Helen Anita Retzner A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Department of Horticulture 1981 ABSTRACT EFFICACY OF GLYPHOSATE (N-PHOSPHONOMETHYL GLYCINE) IN.SELECTIVE TOPICAL APPLICATION FOR HORTICULTURAL CROPPING SYSTEMS BY Helen Anita Retzner The objectives of this study were 1) development of methods for utilization of topical applicators in horticultural cropping systems, 2) determination of critical concentrations and leaf areas for topical glypho- sate (N-phosphonomethylglycine) application, and 3) determination of glyphosate retention on a plant species from topical application. In field studies, barley (Hordeum vulgare L.) windbreaks were more easily removed than rye (Secale cereale L.) using a 10% solution (v/v) glyphosate. A roller applicator caused more phytotoxicity to vegetable crops than a rope wick applicator. Greenhouse studies demonstrated that a 1% glyphosate solution (v/v) did not effectively control weeds or windbreak plant species regardless of leaf area covered. A 5% solution on the three newly expanded leaves of velvetleaf (Abutilon theophra§3;_Medik) was as effective as a 30% solution. For complete kill, velvetleaf must be Helen Anita Retzner treated with 36 mg glyphosate on three leaves. On rye, complete kill was obtained by treating two or three newly expanded leaves with S to 30% solutions. A minimum of 7 mg glyphosate was needed, but unlike velvetleaf just one leaf may be treated. Glyphosate retention increased with concentrations up to 10% after which it decreased. Polyester over acrylic rope delivered more glyphosate than braided nylon. ACKNOWLEDGMENTS I wish to give a special thanks to "Putt", Alan R. Putnam whose time, assistance, guidance and enthusiasm helped me through many rough times. To my guidance committee, William Meggitt and Hugh Price much appreciation is extended for their assistance. And finally, to Bill Chase and the other grad. students in the lab for their sweat and toil, thanks. ii LIST OF TABLE OF CONTENTS TABLES O O C O O O O O O O 0 LIST OF FIGURES . . . . . . . . . . INTRODUCTION 0 O O O O O O O O O O 0 CHAPTER I LITERATURE REVIEW . . . . . Topical Applicators . . . Development of Selective Application . . . . . . Roller Applicator . . . Rope Wick Applicators . Pipe rope wick . . . . Bobar wick applicator A Continuous-belt Herbicide Wiper Glyphosate . . . . . . . . iii Topical O Page vi viii 12 12 16 20 22 CHAPTER Page II MANAGEMENT OF GRASS WINDBREAKS IN VEGETABLE CROPPING SITUATIONS . . . . . . . . 26 Abstract . . . . . . . . . . . . . . . . . 25 Introduction . . . . . . . . . . . . . . . 27 Materials and Methods . . . . . . . . . . . 28 Windbreak Management in Carrots and onions 0 O O O O O O O O O O O O O O O O 28 Windbreak Management in Snap Beans . . . 30 Results and Discussion . . . . . . . . . . 31 Management of Grass Windbreaks in Carrots and Onions . . . . . . . . . . . 31 Windbreak Management and Snap Bean Injury . . . . . . . . . . . . . . . . . 33 III CRITICAL CONCENTRATION AND LEAF AREAS FOR EFFECTIVE TOPICAL GLYPHOSATE APPLICATION . . 43 Abstract . . . . . . . . . . . . . . . . . 43 Introduction . . . . . . . . . . . . . . . 44 Materials and Methods . . . . . . . . . . . 45 General Procedure . . . . . . . . . . . . 45 Velvetleaf Study . . . . . . . . . . . . 47 Rye Study . . . . . . . . . . . . . . . 48 Quackgrass Study . . . . . . . . . . . . 48 Results and Discussion . . . . . . . . . . 49 Velvetleaf Study . . . . . . . . . . . . 49 Rye Study . . . . . . . . . . . . . . . . 57 Quackgrass Study . . . . . . . . . . . . 61 iv CHAPTER IV RETENTION AND PHYTOTOXICITY OF GLYPHOSATE DELIVERED WITH A ROPE WICK APPLICATOR . . Abstract . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . Materials and Methods . . . . . . . . . General Procedure . . . . . . . . . . Retention Study . . . . . . . . . . . Results and Discussion . . . . . . . . BIBLIOGRAPHY. . . . . . . . . . . . . . . . . . . Page 63 63 64 65 65 66 67 72 LIST OF TABLES Table . Page Chapter II 1 Windbreak Kill and Crop Injury After Roller and Wick Application on Muckland vegetables 0 O O O O O O O O O O O I O O O O 32 2 Carrot and Onion Yield After Using Glypho- sate on Roller and Wick Applicators . . . . 34 3 Rye Windbreak Kill and CrOp Injury After Glyphosate Application with Roller and Wick Applicators . . . . . . . . . . . . . . 35 4 Barley Windbreak Kill and CrOp Injury After Glyphosate Application with Roller and Wick Applicators . . . . . . . . . . . . . . 36 5 Yield of Carrots After Using Roller and Wick to Remove Windbreaks . . . . . . . . . 37 6 Windbreak Kill and CrOp Injury After Glyphosate Application with Roller and Wick Applicators . . . . . . . . . . . . . . 39 7 Snap Bean Yield After Using Glyphosate on Roller and Wick Applicators . . . . . . . . 40 8 Snap Bean CrOp Injury and Yield After Using Glyphosate on Roller and Wick Applicators . 42 Chapter III 1 Velvetleaf Kill with Various Concentrations of Glyphosate and Surfactant on Different Leaf Areas 0 O O O O O O O O I O O O O I O O 52 2 Kill of Velvetleaf After Application of 0.5 ml Glyphosate Distributed on Various Leaf Surface Areas . . . . . . . . . . . . . 56 vi Table Page 3 Kill of Velvetleaf After Application of 0.5 ml Distributed on Various Leaf Areas . . 56 4 Kill of Velvetleaf After Application of 0.5 ml Glyphosate at Various Concentrations . . . . . . . . . . . . . . . 57 5 Kill of Wheeler Rye by Applying Glyphosate to the Abaxial Side of Various Leaf surfaces 0 O O O O I O O O O O O O O O O O O 60 6 Kill of Wheeler Rye by Applying Various Concentrations of Glyphosate to the Abaxial Side of Leaves . . . . . . . . . . . 6l 7 Kill of Quackgrass by Various Glyphosate concentrations 0 O O O O O O O O O O O I O O 62 Chapter IV I Effect of Two Rope Types on Retention of Pipe Wick-applied Glyphosate by Rye Measured Immediately After Application . . . . . . . . 68 2 Retention of Pipe Wick-applied Glyphosate by a Single Rye Leaf Measured Immediately After Application . . . . . . . . . . . . . . 68 3 Retention of Pipe Wick-applied Glyphosate by Velvetleaf Measured Immediately After Application 0 O O O I O O O O O O O O O O O O 70 4 Rating of Rye and Velvetleaf Injury Two Weeks After Applying Glyphosate with the Greenhouse PVC Pipe WiCk 0 O O I O O O O O O O O O I O O 71 5 Application of Glyphosate to Wheeler Rye and Velvetleaf Using a Greenhouse PVC Pipe Wick . 71 vii LIST OF FIGURES Figure Chapter I l A schematic diagram of a box type recirculating sprayer (26). . . . . . . . . 2a A roller applicator manufactured by Farmers Union Gill Co.,; Roseau, MN . . . . . . . . 2b Side view of the roller applicator . . . . . 3a A PVC pipe wick applicator constructed by the author . . . . . . . . . . . . . . . . 3b A pipe wick applicator manufactured by Sprayrite Manufacturing Co., West Helena ' AR 0 O O O O I O O O O O O I O O 0 4a A Bobar pipe wick applicator manufactured by ‘ Bobar Co.; Hale Center, TX . . . . . . . . 4b Side view of Bobar pipe wick applicator showing piping from reservoir to ropes . . Chapter III 1 Fresh weight reduction of velvetleaf as influenced by concentrations of glyphosate and leaf areas treated . . . . . . . . . . 2 Fresh weight reduction of velvetleaf as influenced by concentrations of glyphosate, surfactant and leaf areas treated . . . . . 3 Fresh weight reduction of 'Wheeler' rye as influenced by concentrations of glyphosate and leaf areas treated . . . . . . . . . . viii Page 14 14 18 18 51 55 59 INTRODUCTION In most large-scale farming operations, farmers control weeds by the use of chemical herbicides and mechanized cultivators. Preemergence herbicides in many crops often do not provide complete weed suppression because of inadequate soil moisture, other unfavorable environmental factors, or emergence of tolerant species. This results in weed escapes which may protrude above the crop. Unfortunately few selective post-emergence herbicides are available in numerous crops such as soybeans (Glycine max (L.) Merr.), cotton (Gossypium hi‘rsutum L.) , peanuts (Arachis hypogaea L. ), strawberries (Fragaria x ananassa Duch.) , potatoes Solanum tuberosum L.), etc. Alternative methods for removal of weed escapes are cultivation and manual labor. With the increasing costs of energy and labor, leading to higher production costs, it is inevitable a more efficient means he found. Minotti estimated that in the northeastern United States in 1980, vegetable losses due to weeds totaled $27.6 million. Of this, 62% was for control measures such as herbicide cost and application, cultivation, handweeding, and extra land preparation. The remaining crOp loss was attributed to weed competition, herbicide injury, reduc- tion in quality, and extra harvesting expense.(30) l Attempts to provide broad spectrum post-emergence control of both annual and perennial weeds was inhibited by the fact that many systemic herbicides are non-selective ie. glyphosate (3). To help overcome this, directed sprays, foams, and granular formulations were used. McWhorter found over-the-top or directed sprays of glyphosate effectively controlled johnsongrass (Sorghum halepense (L) Pers.), but significantly reduced soybean yields (27). A definite need still existed for a spray that could be applied topically to weeds and crops that would give effective control, but cause negligible damage to crops. Recirculating Sprayers, roller applicators, rope wick applicators, and continuous belt wipers have the advantage of being able to direct non-selective herbicides to weeds growing above the crops, therefore minimizing injury to crop plants. Since the herbicide is applied to the weed and not the soil surface, soil residue problems are avoided. Selective topical application may provide less drift, reduce the amount of herbicide needed per acre, and reduce exposure to the operator. Topical applicators are a great aid in improving herbicide selectivity, but are not meant to replace normal weed control practices. They are merely a component of a total weed control program. Objectives of this work were: 1) development of methods for utilization of topical applicators in horticultural cropping systems; 2) determination of critical concentrations and leaf areas for effective topical glyphosate application; 3) determination of glyphosate retention by plant species using a topical applicator. CHAPTER I LITERATURE REVIEW Topical Applicators Development of Selective Topical Application In the mid 1960's at Stoneville, Mississippi, Barrentine and McWhorter developed a recirculating sprayer (RCS) for applying herbicides in row crops to weeds taller than the cr0p (26). A RCS does exactly what its name implies. Herbicide solutions are applied through solid stream nozzles above and at right angles to the rows (figure 1). Any herbicide not contacting a plant is trapped in a catch box and recirculated. This prevents much of the waste found in normal spray systems (26). First tests were conducted using MSMA for control of johnsongrass in soybeans (26). Later, cocklebur (Xanthium strumarium L.), sesbania (Sesbania exaltata (Raf.) Rydb.), and redroot pigweed (Amaranthus retroflexus L.) were selectively controlled in soybeans using 2,4—D and 2,4-DB (27). In the early 1970's there was increased interest in selective postemergence herbicides along with the intro- duction of the nonselective translocated herbicide, glyphosate. These early tests showed much potential for Fig. l. A schematic diagram of a box type recirculating sprayer (26). n zONNrmm \ IV I $.Al.lnh¥luh‘vm“rlll|ldn . ~ 4'”? -. .- .. a 22:: é 43>? I _ _tom><:< .mmscmz ;.\\oc>mm _:zm .‘. ummmmcmm \\\ mmmcr>403 e e \_U a : a. e. smmmmcmmmmrfimptzm I- Illlv (\wwlq>zx _ F \ wcgv\\, VII/mommmz perennial weed control using glyphosate (3). By the mid 1970's, wipers, applicators which apply herbicide by wiping the chemical on to weeds, were on the market. These applicators (rollers, rope wick, and endless belt) had several advantages over the recirculating sprayer: (1) no spray nozzles, strainers or returns to adjust or replace; (2) less chance of drift or drip in windy situations; (3) can be used in both broadcast and row-crop situations; (4) herbicide is not recirculated so no dirt or dust contaminates solution; (5) application of chemical from lowest target area to top of plant. Roller Applicators Roller applicators deliver the herbicide from a saturated surface of a rotating cylinder. The roller applicator1 consists of a 25.4 cm diameter steel pipe covered with nylon-dacron jute backed, 1.27 cm cut pile carpeting (figure 2). A wetting pipe, PVC plumbing, with .04-.08 cm holes every 5.08 cm along the bottom is located approximately 5.08 above the carpeted steel pipe. The wetting pipe is connected to the holding tank. The chemical spray is pumped from the plastic 7.57 L holding tank through the wetting pipe. The chemical flows through the small holes in the wetting pipe onto 1Manufactured by the Farmers Union Grill Co.; Roseau, MN. Fig, 2a. A roller applicator manufactured by Farmers Union Gill.; Roseau, MN. Fig. 2b. Side view of the roller applicator. 10 the carpeted steel pipe which is revolving in a clockwise manner at 40 to 50 rpm. The rotation enhances saturation of the entire roller surface, and helps prevent drip. Immediately behind the wetting pipe is a 15.24 cm wide .64 cm thick rubberized canvas. This canvas brushes lightly along the entire length of the roller. The purpose of the canvas is to help cause foaming of the glyphosate solution. This helps prevent dripping and incorporates the foam into the knap of the carpet. A saturated rotating (6 M) roller will hold 22.7-30.3 L of solution without dripping. Commercially available models treat areas as much as 6 meters wide, travel 3 to 6 mph, and apply an average .84 L/ha. The roller can be mounted on a versatile swather power unit after the swathing unit is removed, by 3 point hitch, or built to fit a High Boy sprayer. Flow rate, roller speed and height are hydraulically driven, and can be regulated by gauges. As the roller moves through the field the pressure from the weeds which come in contact with the roller causes the roller to release the chemical. The weed is bent over so it can go under the roller and the entire plant acropetal to the point of contact is treated. Various factors influence the effectiveness of the roller applicators, but of main concern are height ll differentials between weeds and crop and maintenance of 40-50 rpm roller speed. In bluegrass seed fields a 10.16 cm height difference is needed to achieve 99% control of Reed canarygrass (Phalaris arundinacealn) and quackgrass seed producing inflorescenceS(8). Common cocklebur was controlled 43% and kOChia (Kochia scoparia (L) Schrad) 84% in sugar beets (Beta vulgaris L.) (45). Effectiveness of application was dependent on height of weeds in relation to sugarbeets. Since there is no time in the season when all weeds are above the canopy 100% weed control was impossible to achieve. Common milkweed (Asclepias syriaca L.) control in soybeans was poor due to insufficient wetting of roller (17). The effectiveness of one pass was reduced because of inability to keep applicator wet enough with the weed pressure present. According to Binning, the roller applicator should be better suited to dense weed stands since it can be wetted as needed, while the pipe wick depends on capillary action. For proper wetting a constant 40-50 rpm must be maintained to keep the roller equally saturated, foaming, and not dripping or splattering. In some studies, speed or concentration of glyphosate have had little influence on weed control (17, 25, 29). Volunteer corn (up to 1943 plants/ha) was effectively controlled with varying speeds and concentrations. The 12 concentration most used is a 5% solution (v/v) with a range of 2.5 to 20% solution (v/v) (18). In a 1980 survey of Nebraska farmers who use roller applicators, 36% said they would modify the roller by making it a front mount, changing the power unit, or adding a pump, but 93% said they would use it again (18). ROpe Wick Applicators Pipe rope wick applicators Pipe rope wicks are mechanically simple and economical to construct (9). A typical pipe rOpe wick applicator consists of 7.62 cm PVC pipe with a 7.62 cm PVC plug cemented into one end of the pipe and a 7.62 cm PVC elbow with removable plug to the other (figure 3). The two rows of 1.27 cm nylon rope wicks are 3.8 cm apart and are suspended from the lower side of the pipe. They are overlapped, leaving no gaps for weeds to escape. To hold the wicks in place 1.27 cm compression fittings or grommets are used. With the compression fittings, 2, 1.27 cm, rubber O-ring washers are needed to help prevent dripping. Two advantages of compression fittings are they can be loosened or tightened to regulate herbicide flow rate, and the wicks are easily removed for cleaning or replacement. Grommets are less expensive and easier to insert in the pipe initially than compression fittings. To help prevent dripping, glue may be used around the grommet. 13 Fig. 3a. A PVC pipe wick applicator constructed by the author. Fig. 3b. A pipe wick applicator manufactured by Sprayrite Manufacturing Co., West Helena, AR. 14 15 Yellow rubber vinyl cement is not suggested because it penetrates the rope and reduces flow. Dale (ll) advises black rubber vinyl cement since it does not significantly reduce flow of herbicides. Presently in most rope wick applicators, solid braid soft nylon rope is used. Monsanto representatives report that diamond braid polyester over acrylic rope is 50% better in some weed situations than the plain nylon rOpe (2). The new rope gives excellent wicking because of the acrylic fiber interior and the outer polyester fibers give good wear. Length of rope also influences weed control. 10.16 cm segments were found to be superior to both 20.32 cm and 30.48 cm segments (2). In heavy weed pOpulations the smaller segments will saturate quicker. The PVC rope wick is very versatile. It can be made any length desired, mounted to the front or back of a tractor or other conveyance, and in small plots carried by one or two people. For best results with the PVC rope wick: 1) Pipe should be vented to prevent air locking. 2) Reservoir should be kept full. 3) Grommets or compression fittings must be properly adjusted or will restrict flow of chemical. 4) Speed should be reduced in high density weed stands. 16 Description of Bobar applicator The Bobar1 (figure 4) is a commercially available rope wick applicator. Unlike the pipe rope wick, the rOpes are suspended from a metal frame and force fed from a 7.6 L reservoir 25.4 cm above the ropes. The basic metal frame is 204 cm long by 66 cm wide. Along both sides of the length of the frame are 1.9 cm feeder pipes with 23, 1.27 cm spouts spaced every 8 cm. To attach the ropes to the spouts, a 5.08 cm segment of 1.27 cm heat sensitive tubing or plastic tubing and glue is placed on the ends of each rOpe. (If glue is used the same considerations mentioned above in the pipe rope wick description should be recalled.) The first spout on one side is offset 18.5 cm from the first spout on the opposite side. Therefore when the rOpes are suspended across the frame they are angled. This overlaps the ropes leaving no gaps from which weeds can escape. The reservoir is 10.16 cm PVC pipe. Herbicide flows gravitationally from the reservoir through 1.9 cm tubing to the feeder tubes, and by capillary action the ropes are saturated. Like the pipe rope wick the reservoir should be vented and speed reduced for high weed stands. The diamond braid polyester over acrylic rOpe should not be used on the Bobar for it may cause excessive dripping (2). ‘Manufactured by Bobar Co.; Hale Center, Texas. 17 Fig. 4a. A Bobar pipe wick applicator manufactured by Bobar Co.; Hale Center, TX. Fig. 4b. Side View of Bobar pipe wick applicator showing piping from reservoir to ropes. 18 19 Experimental results In 1980, wick applicators were used on 6 to 8 million hectares (22). Simplicity, economy and lack of moving parts is reason for the wide spread appeal of rope wicks. Many styles are available, but the principal is the same in all. As in a kerosene lamp, glyphosate moves by capillary action saturating the rOpe wicks (11). Dale, developer of the rOpe wick applicator, noted that the concentration of solution of glyphosate in the reservoir affected rate of movement of solution in the wick (13). By adding water to glyphosate the total volume of solution delivered increased. Optimum rates of acid glyphosate delivered were ratios of 1:2 to 1:4 glyphosate to water (v/v). Using a 1:2 ratio Dale was able to control 40 to 70% of the johnsongrass in 1 application with a pipe wick. Going to 2 applications gave 89 to 97% control of john- songrass (13). Speed was a critical factor for control of common milkweed (17). Satisfactory kill was obtained at 2 and 4 mph but not 6 mph. For heavy weed stands in straw- berries, the Bobar gave 100% control with l or 2 passes regardless of speed (3 and 1.5 mph) or concentration (20 and 33%) (25). In this situation the pipe wick was not as effective. The pipe wick was unable to keep ropes wet enough in high weed densities. This is partially 20 due to the fact that pipe wicks depend entirely on a passive capillary flow, while the Bobar is pressure fed by gravity. In asparagus (Asparagus officinalis L.) the pipe wick was more successful in controlling johnsongrass and smooth pigweed because of smaller plot sizes (25). The control of volunteer corn in soybeans was possible with a 5% solution (v/v) glyphosate (17). In comparison with the recirculating sprayer (RCS), the rope wick applicator gave significantly less injury to the soybeans because of no glyphosate splash. The RCS applies more herbicide on the weed and injury symptoms are evident more rapidly than with the rOpe wick applicator. But as Fawcett showed, after nine weeks plots were as free of hemp dogbane (Apocgnum cannabinum L.) with the rope wick applicator as with the RC8. A Continuous-belt Herbicide Wiper The continuous-belt herbicide wiper was constructed by W. V. Welker while at the New Jersey Agriculture Experiment Station, New Brunswick, NJ (42). It consists of plastic sponges 5 cm. by 5 cm. in cross section glued to a continuous v-belt. With the aid of pulleys, the v-belt with the sponges attached is wetted by passing through a reservior which contains the herbicide solution. After the v-belt sponge absorbs from the reservior a 21 variable pressure wheel squeezes out excess liquid. The pressure wheel can be adjusted to help prevent drip, but at the same time maintain adequate wetting of weeds in various densities. The belt moves horizontally, perpendicular with the forward movement of the wiper across the field. It treats an area 2 m wide, and travels best at 3.2 km/hr. At 6.4 km/hr the excessive bouncing of the wiper promotes dripping. The wiper is mounted on 2 bicycle tires, and is self-propelled by a 2.2 kw gasoline powered, air cooled engine. A series of belts and pulleys move the wheels and v-belt. Various chemicals can be used with the wiper since the v-belt can be easily removed, and both the sponge and tank cleaned. This fact plus the wiper's simplicity and manuverability make it suitable for experimental purposes. The continuous-belt wiper was developed for use in cranberry (Vaccinium macrocarpon Ait) bogs. Three herbicides, glyphosate, paraquat, and dalapon, were tested for weed control using the wiper (42). Ninety days after treatment all plots were essentially weed free (90 to 100% control). There was no foliar injury to the cranberry vines, and yield was not reduced by the wiper. The year of treatment, paraquat increased 22 yields because weeds were immediately desiccated. Glyphosate increased cranberry yields in subsequent years with continued control. Apparently, the wiper sufficiently wets the foliage of the weeds without dripping on the crop. For general use in cranberry bogs and other crops, Welker suggests covering the sponge with canvas, thus necessitating an increase in sponge size. The wiper could also be mounted on a tractor, increasing its versatility. Glyphosate In 1971, Monsanto introduced a new, nonselective, postemergence herbicide, N-(phosphonomethy1)glycine (3). The formulated isopropylamine salt of this compound is better known as Roundup R (glyphosate). Although no other compound in this family has been reported to be a herbicide, the analog, N,N-bis(phosphonomethyl)glycine (glyphosine)is a growth regulator (1). Glyphosate possesses a wide spectrum of activity including deep rooted perennial, annual and biennial species including grasses, sedges and broadleaf weeds. Most annuals and biennials can be controlled with .34 to 1.12 kg/ha. Perennials may require up to 4.48 kg/ha (1). To gain selectivity, directed sprays have been used in orchards, vineyards, and various crOps (24, 27). With 23 the advent of topical applicators, glyphosate's uses may be greatly extended. Several factors have contributed to glyphosate's success. It has a low molecular weight (169.1) and compared to other herbicides a high solubility in water (1.2%) (1). These factors may enhance absorption and translocation in the plant. Environmental factors which increase uptake include high relative humidity and high soil moisture (14, 28, 43). Optimum temperatures vary from species to species. Johnsongrass (Sorghum halepense (L) Pers.) transports glyphosate best at 35C, while soybeans (Glycine max (L) Merr.) are more susceptiable at 24 C (28). Studies with 1"C-labeled glyphosate have shown that plants do not metabolize glyphosate to a significant degree. This allows glyphosate to move acropetally to younger tissue and basipetally with phloem assimilates to underground propagules of perennial species (4, 35). Glyphosate is readily adsorbed by soil (clay and organic matter) possibly through the phosphonic acid moiety (20, 38, 39). The chemical does not leach and is rapidly degraded by the microflora. Normally, the half life is less than 60 days (1). The lack of pre- emergence activity, the binding to soil, and rapid degradation permit the seeding of many crops almost immediately after application. 24 Finally, glyphosate has a low toxicity. The oral LDso to rats is 4320 mg/kg (1). The mode of action of glyphosate first appeared to be the inhibition of the aromatic amino acid biosynthesis pathway. The growth of Lemma gibba was inhibited by glyphosate but could be reversed with the addition of L-phenylalanine to the nutrient solution (23). In whole plants, the supplemental feeding of phenylalanine (Phe), tyrosine (Tyr) gnui tryptophan (Try) did not substantially reverse the inhibition of transpiration (35). It was discovered that levels of endogenous Tyr and Phe were 50% reduced in glyphosate treated plants, and phenylalanine ammonia-lyase(PAL) was increased. A new hypothesis arose suggesting PAL may cause an increase in phenols which eventually kill the plant (37). But when coumaric and cinnamic acids (phenols produced by PAL) were continually added there was no effect on transpiration. In other studies the analog, glyphosine and gly- phosate's metabolites, aminomethyl phosphonic acid (AMPA), sarcosine, and glycine were tested for their role in PAL activity (21). Glyphosine did increase PAL activity but not to the same extent as glyphosate. The metabolites had no effect. Recently it was found that glyphosate inhibited incorporation of shikimate into Phe, Tyr or Try (22). The 25 addition of chorismate alleviated the inhibition. Several enzymes are involved in the transformation, but 5- enolpyruvylshikimate 3—phosphate synthase appears to be the site of action for glyphosate. Many biochemical studies have been conducted but more are needed. Glyphosate effects a wide variety of plant organs suggesting there may not be just one mode of action. CHAPTER II MANAGEMENT OF GRASS WINDBREAKS IN VEGETABLE CROPPING SITUATIONS ABSTRACT The roller and Bobar pipe wick applicators were evaluated for their effectiveness in removing rye and barley grass windbreaks in carrots, onions and snap beans. The first year, the roller with 10% glyphosate gave better rye kill than the 5% rate. The wick gave better kill at both rates, but reduced yield of carrots at the 10% concentration. Barley control was complete with both applicators and rates. Highest carrot yields were attained from the plots using the roller applicator with 5 and 10% glyphosate on rye windbreaks. Onion yields were not affected by type of Windbreak, applicator or concentration used. In the second year, undercutting was compared to the two rates on both applicators. Undercutting did not injure carrots, but windbreaks were ineffectively removed. The roller with 5% glyphosate did injure carrots about 40% while removing 85% of the rye. Carrot yields were decreased by both concentrations with the wick after removing rye windbreaks. Removal of barley did not injure carrots or decrease yields. In snap beans, glyphosate applied by the roller and wick effectively killed rye and barley windbreaks. The yield 26 27 was not reduced by any of the treatments. The second year, the wick application produced less bean injury when removing rye with 5 and 50% solutions, but crop yield was unaffected. The roller applicator reduced total plant and pod weight regardless of rate or windbreak. Introduction Rye (Secale cereale L.) or barley (Hordeum vulgare L.) windbreaks are commonly used to prevent wind erosion on both muckland and mineral soil vegetable production systems in Michigan. Undercutting is the present method used to remove grass windbreaks in these crOpping situ- ations. This is accomplished with a narrow blade moved 5.1 cm below the soil surface which cuts the roots off the plant. To be effective, this Operation often must be repeated. In the event grass windbreaks are not out completely and reroot, they must be removed manually. Manual hoeing costs were about $35.00 per acre in 1978 and required numerous laborers (16). Besides requiring more fuel, the practice of under-cutting may compact the soil, disturb the soil surface, and destroy most of the mulch effect possible from grass windbreaks. With the advent of glyphosate, a non-selective systemic herbicide (3), over-the-tOp or directed spray could be used to control annual and perennial weeds (1,3). Unfortunately these methods also provide toxicity to crop plants (27). Recently, the use of glyphosate on 28 roller and wick applicators has shown promise for con- trolling many annual and perennial weeds without injuring crop plants. With a height differential between the weed and crop, the herbicide is wiped on the weed but not the crop. This precise application of herbicide by the roller and wick minimizes herbicide drift and crop injury. Since the herbicide is placed directly on the weed little chemical reaches the soil. Selleck has successfully controlled barnyardgrass (Echinochloa crus-galli (L) Beauv.) and lambsquarters (Chenopodium album L.) in Katahdin potatoes (Solanum tuberosum L.) 80% or better using a 10% solution (v/v) glyphosate on a roller applicator (37). Other tests have shown a 5% (v/v) solution of glyphosate on a rOpe wick removed volunteer corn (Zea mays L. subsp. mays) from soybeans (Glycine max (L) merr.) with 0% damage to the soybeans (17). Our main objectives in this study were to determine the efficiency of roller and wick applicators for improved management of various grass windbreaks, and to define rates necessary for satisfactory kill and adequate crOp tolerance. Materials and Methods Windbreak Management in Carrots and Onions Field experiments were conducted in 1979 and 1980 at the Muck.Experimental Station, Bath, Michigan, to investigate the use of roller and wick applicators to 29 remove grass windbreaks. The experiments were conducted on a Houghton muck using a randomized complete block (RCB) design with a plot size of 5 rows, 2.44 m by 7.62 m in 1979 and 2.44 m by 6.10 m in 1980. Each treatment was replicated 4 times. Treatments included 5 and 10% solutions (v/v) glyphosate applied with the.roller or Bobar wick applicator, mounted by three point hitch. In each plot, rows of either'Primus II'barley (Hordeum vulgare L.) or'Wheeler' rye (Secalecereale L.) were alternated with the crops. On July 10, 1979 and May 14, 1980 the grass windbreaks were planted. 'Spartan Banner' onions (Allium cepa L.) and 'Spartan Classic' carrots (Daucus carota L. subsp. sativus (Hoffm.) Arcang.) were planted July 28, 1979. 'Early Yellow Globe' onions and 'Spartan Fancy' carrots were planted on May 14, 1980. For comparison, three additional treatments were included; undercutting a rye and barley wind- break and a control without windbreak. To control broadleaf weeds in the experimental area, nitrofen at 1.12 kg/ha was applied as needed. Glyphosate applications were made on August 9, 1979 and June 11, 1980. The tractor was driven at 2.5 mph, and the roller operated at 45 rpm. Stage of growth at time of treating was: cabbage - 4 true leaves; onion - 2 true leaves; carrot - 2 true leaves; rye - 25.4 to 30.5 cm tall; barley - 30 30.5 to 38.1 cm tall. In 1980, onions had a true leaf, carrots had 2 true leaves, and the rye and barley were 12.7 and 21.6 cm tall, respectively. Undercutting was done twice as in atypical commercial operation. The first was accomplished at the same time as the chemical treatments and the second, one week later. Visual ratings for percent Windbreak kill and crop injury on a 0 (no effect) to 10 (complete kill) scale were made 2 weeks after treatment. At carrot maturity, each plot minus a meter from each end was harvested for yield determinations. Since the crOps were planted late in 1979, entire onion plants were harvested 10 weeks after planting. Windbreak Management in Snap Beans 'Spartan Arrow' snap beans (Phaseolus vulgaris L.) were grown in plots 2.44 m wide by 7.62 m long. The snap bean row was between the windbreaks'Primus II' barley or'Wheeler'rye. Each experiment was conducted as a RCB with three replications for each treatment. In 1979 the experimental area was located on a Spinks sandy loam, and in 1980 on a Dryden sandy loam. Wind- breaks were planted July 3, 1979, and June 12, 1980. In 1979, snap beans were planted two weeks after the windbreaks and in 1980 they were planted at the same time as the windbreaks. 31 Applications of 5 and 10% solutions(v/v) glyphosate were made with the roller and Bobar wick on August 6, 1979 and July 10, 1980. Additional treatments in 1980 included a no windbreak control, undercutting of a rye and barley windbreak and a 50% solution MUN” glyphosate on the wick. CrOp injury and windbreak kill were rated two weeks after application. Bean yields were taken at plant maturity. Two additional topical applications were made on August 5, 1980 and August 19, 1980 to determine the degree of crop injury resulting from the removal of weed escapes. Rates and applicators used are the same as above. Plant number and yields were obtained at harvest. Results and Discussion Management of Grass Windbreaks in Carrots and Onions In 1979, glyphosate at 5 and 10% solution (v/v) applied by roller and wick applicators gave significant differences between treatments for both windbreak kill .and injury to carrots (table 1). The roller with 10% salyphosate gave better rye kill than the 5% rate. Illthough the wick gave better kill at both rates than the :roller applicator, there was more injury on carrots at the 10% concentration . Barley control was excellent with both applicators iand concentrations. Yields from these plots show that 32 TABLE 1 WINDBREAK KILL AND CROP INJURY AFTER ROLLER AND WICK APPLI- CATION ON MUCKLAND VEGETABLES Ratinga Conc. Applicator (%) Rye Barley Carrot Onion Roller 5 5.5 A 8.5 A 0.6 A 0.9 A 10 6.5 B 8.5 A 0.6 A 0.8 A Wick 5 7.8 C 8.5 A 0.8 AB 1.1 A 10 7.0 C 9.0 A 1.3 B 1.4 A aMeans followed by the same letter were not signi- ficantly different as determined by the LSD test at the 5% level. 33 the roller applicator with 5 and 10% glyphosate using a rye windbreak gave significantly higher carrot yields (table 2). Since the rye was removed less effectively by the roller at both rates, perhaps less glyphosate contact also occurred on the carrots. There were no differences in onion yields between applicators, rates, or various wind- breaks. The onion due to its morphology has less horizontal leaf surface than the carrot so there may be less chance of glyphosate dripping onto the onion during application. No data on cabbage is presented due to poor stand from planting. The following year, the 2 rates on both applicators were compared with undercutting (tables 3 & 4). (Onion maggot severely reduced onion stand so no data is presented.) With undercutting there was no apparent injury to the carrots but only 50 to 60% of the windbreaks were killed. In the removal of rye, the roller with 5% glyphosate injured carrots up to 40% while rye windbreak kill was 85% (table 3). Between applicators or rates there were no differences in barley kill or carrot injury (table 4). Carrot yields were not reduced by the removal of barley windbreaks regardless of concentration or applicator (table 5). After removing the rye windbreaks, the wick with a 10% solution, and roller with a 5% solution decreased the yield of carrots. 34 TABLE 2 CARROT AND ONION YIELD AFTER USING GLYPHOSATE ON ROLLER AND WICK APPLICATORS. Total Yield (MT/ha)a Conc. Windbreak Applicator (%) Carrot Onion Rye Roller 5 164 B 33 10 169 B 27 Wick 5 146 AB 33 10 140 AB 33 Barley Roller 5 149 A 34 10 155 A 33 Wick 5 136 A 26 10 142 A 30 aMeans followed by the same letter were not significantly different as determined by the LSD test at the 5% level. 35 TABLE 3 RYE WINDBREAK KILL AND CROP INJURY AFTER GLYPHOSATE APPLICATION WITH ROLLER AND WICK APPLICATORS. Ratinga Conc. Treatments (%) Rye Carrots Undercut 5.0 A 0.0 A Roller 5 8.5 B 4.0 C 10 8.3 B 3.0 BC Wick 5 7.0 B 2.0 B 10 7.3 B 2.5 BC aMeans followed by the same letter were not significantly different as determined by the LSD test at the 5% level. 36 TABLE 4 BARLEY WINDBREAK KILL AND CROP INJURY AFTER GLYPHOSATE APPLICATION WITH ROLLER AND WICK APPLICATORS. Ratinga Conc. Treatments (%) Barley Carrots Undercut 6.3 A 0.0 A Roller 5 8.3 B 2.3 B 10 8.3 B 2.3 B Wick ' 5 7.0 AB 2.3 B 10 6.8 AB 1.5 AB aMeans followed by the same letter were not significantly different as determined by the LSD test at the 5% level. 37 TABLE 5 YIELD OF CARROTS AFTER USING ROLLER AND WICK TO REMOVE WINDBREAKS. Carrot Yield (MT/ha)a Conc. Applicator (%) Rye Barley Control 106.66 CDEF 106.66 CDEF Undercut 114.69 F 113.80 EF Roller 5 73.53 A 93.48 BCD 10 91.73 BC 103.24 CDBF Wick 5 109.17 DEF 97.59 BCD 10 86.78 AB 107.19 CDEF aMeans followed 5% level. by the same letter were not signi- ficantly different as determined by the LSD test at the 38 In 1980, the windbreaks were sown the same time as the crops. At time of herbicide application, barley was 16.5 cm above the crop while rye was only 7.6 cm above. Barley has a more upright growth habit while rye tillers are more prostrate. In bluegrass seed fields a 10.2 cm height difference between crop and weed was needed to give 99% control of reed canarygrass and quackgrass (8). Likewise, the greater height differential between barley and the crop resulted in less damage to the crop while effectively removing the barley windbreak. Wilson noted in sugarbeets that the effectiveness of the appli- cators was dependent on height of the weed in relation to sugarbeet (45). Windbreak Management in Snap Beans In snap bean plantings on mineral soil in 1979, glyphosate applied by roller and wick effectively killed rye and barley windbreaks (table 6). On this site, the only significant crop injury was produced by the 10% concentration of glyphosate on the wick. There is no sig- nificant difference in bean yield (table 7). The variability in this experiment was extremely high which made it impos- sible to obtain significant yield difference. Since rye tillers grow more prostrate, it is harder for the driver of the applicator to apply the chemical accurately. 39 TABLE 6 WINDBREAK KILL AND CROP INJURY AFTER GLYPHOSATE APPLICATION WITH ROLLER AND WICK APPLICATORS. Ratinga Conc. Applicator (%) Snap Bean Rye Barley Roller 5 2.0 A 8.0 A 8.7 A 10 2.0 A 9.0 A 8.7 A Wick 5 2.8 A 6.7 A 7.7 A 10 3.8 B 7.0 A 8.7 A aMeans followed by the same letter were not signifi- cantly different as determined by the LSD test at the 5% level. 4O TABLE 7 SNAP BEAN YIELD AFTER USING GLYPHOSATE ON ROLLER AND WICK APPLICATORS. Bean Yield (MT/ha)a Conc. Windbreak Applicator (%) Total Plant Pods Rye Roller 5 17.8 8.8 10 10.5 5.8 Wick 5 11.7 6.2 10 6.2 2.9 Barley Roller 5 10.0 4.9 10 15.5 8.3 Wick 5 16.0 8.5 10 12.8 7.1 aMeans were not significantly different as determined by the LSD test at the 5% level. 41 In 1980, besides removing the grass windbreaks, repeated applications were made throughout the season to remove escaped weeds. The wick had significantly less cr0p injury on rye with 5 and 50% solutions. The concen- tration of the solution (v/v) glyphosate in the reservoir affects the rate of movement of solution in the wick (13). In comparison to a 10% solution (v/v) glyphosate, the 5% solution flows just as easily through the wick, but less acid glyphosate is applied. There is then less chance for injury. A 50% solution is more viscous, does not saturate the wicks as easily, and does not deliver as much acid glyphosate onto the plant. The total plant yield was no greater from using a 5 or 50% solution than other wick or undercutting treatments (table 8). In barley, undercutting gave no apparent crop damage while both applicators and rates did. The roller applicator reduced total plant and pod weight regardless of rate or windbreak. Repeated applica- tions with the wick with 5, 10 and 50% solutions (v/v) glyphosate did not reduce yield from the control. As Binning states, the roller is better at dense stands of weeds than the wick (5). With very few escape weeds present there was a greater chance of splatter or drip from the roller. 42 .umwu omq map an pwsHEumuop mm Hm>ma mm onu um DawsoMMHp wausmofimasmfim nos mums sEsHoo mama map segues Hopped mama on» ho po3o-om mammzo m4 n.0H om< n.HN m m.~ om one m.~H om< o.m~ m m.m oa om< >.mH on m.mm m< m.a m xOHz < v.5 < m.ma m< w.H oa < v.5 m< m.ma m m.m m umaaom on m.ma o m.m~ a 0.0 maauusoumnes amsumm om< n.~a om< m.m~ 4 o.o om m< m.HH om< ~.vm m m.m oa m< m.HH om< m.a~ < o.o m xoflz < v.5 m< v.va m m.~ 0H < m.m m< v.0a m m.m m umaaom o H.ma o ~.vm a o.o maauuaoumwas mam om v.5H o m.m~ Houucoonmso: moon “swam Hmuoa wnsmsH mouu va Houmoafimmm xmmnncsaz .ocoo mimr\ezv esmaw ammm .meBfiqummd MUHB 024 mmflqom ZO m9¢momquu GZHmD mMBmd DQmHN Q24 MmDhZH momo dem m¢Zm m mamfiB CHAPTER III CRITICAL CONCENTRATIONS AND LEAF AREAS FOR EFFECTIVE TOPICAL GLYPHOSATE APPLICATION ABSTRACT Greenhouse studies were conducted to determine the phytotoxicity attained from treating only the most recently expanded leaf, the first and second recently expanded leaves, or the top three newly expanded leaves of rye (Secale cereale L.), velvet leaf (Abutilon theophrasti Medik.), and quackgrass (Agropyron repens L. Beauv.) simulating selective topical glyphosate applications of 1, 5, 10, 20 and 30% solutions (v/v). In all plant species tested, a 1% solution (v/v) gave less reduction in plant weight than all other rates. Solutions of 5 to 30% did not always kill the plant (dependent on treated area) but stunted it sufficiently to reduce competition to the cr0p. In the control of velvetleaf,application on 3 leaves gave better kill than 2 leaves and both were better than 1 leaf. When 3 leaves were treated, there were no differences among concentrations of 5 to 30%. On rye, effective kill resulted from application to either 2 or 3 leaves. The interactions indicated that a 5% solution on 2 or 3 43 44 leaves was comparable with a 20 or 30% solution on 1, 2 or 3 leaves. Number of leaves treated did not influence control of quackgrass, but a 5% rate was necessary to prevent regrowth. Introduction Successful control of annual and perennial weeds using topical applicators to apply herbicides depends on adequate coverage of the foliage at a critical concentra- tion. The herbicide then can be translocated in sufficient quantities to provide toxicity to the entire plant. Yarborough tested the effect of wiping 2,4-D or glyphosate on all or half the foliage of black barrenberry (Aronia melanocarpa Michx) (47). He found survival was not influenced by placement of herbicides on all or half the foliage. But the question of what is the minimum leaf area needed to be covered for an herbicide to be effective still remains to be answered. Smartweed (Polygonum pennsylvanicum L.) was poorly controlled in potatoes (Solanum tuberosum L.) by the roller applicator because a height difference was lacking between the crop and weed. (37). This did not allow for a sufficient leaf area to be treated, thus the weed was not killed. Can lack of leaf area be compensated for with increased rates? A 7.5% glyphosate solution (v/v) was applied with the recirculating sprayer, while 33% 45 glyphosate was used in a rope wick applicator. More herbicide was place on the weed by the sprayer, but nine weeks after treatment there was no difference between plots in hemp dogbane (Apocynum cannabinum L.) control (17). To date no data has clearly defined the interaction between concentration of herbicide required and leaf coverage needed to get effective kill. The objectives in this study were to determine critical leaf coverage needed and define rates of glyphosate necessary for satisfactory kill of several plant species. Materials and Methods General Procedure A BadgerR1 professional type hobby and touch-up air- brush was used to apply formulated glyphosate solutions in such small quantities as .1 cc or .2 cc and to maintain this amount in a given leaf area. The tubing included with the airbrush was replaced with an .16 cm outside diam. tube to reduce the amount of chemical lost. A .3 m1 glass reaction vial was used to insure against chemical loss. The vial was held in place on the airbrush a styrofoam disk with a 1Manufactured by Badger Air-Brush Co., Franklin Park, IL. 46 hole cut for the vial was placed in the spray cap. An alternative method is to place a piece of styrofoam with a hole bored out for the vial in the spray jar included with the airbrush. Either method securely holds the vial in place while spraying, but the latter method requires more time to screw the jar on and off between applications. All plants were grown in a greenhouse at 30: C-day, 20 C-night, 30 to 60 % relative humidity with a supplemental lighting photoperiod of 16 hours. The plants were grown at least two weeks prior to treatment under metal halide lamps to provide leaf surfaces more typical of those grown under field conditions. Seeds or rhizomes of the test species were planted in plastic pots filled with a soil:peat:sand (1:1:1 v/v/v) potting media. Plants were surfaced watered and fertilized twice weekly with a 20-20-20 water soluble fertilizer solution at 2 g/l. Glyphosate at 1, 5, 10, 20 and 30% (v/v) solution was applied at a volume of .1 cc to the first newly expanded leaf, .3 cc to the first and second newly expanded leaves, or .5 cc to the top three newly expanded leaves. The apical meristem was not treated since in all species it is located lower than the treated leaves. In a field situation, it is these newly expanded upper 47 leaves which would receive treatment most frequently by a topical applicator. A randomized complete block design was used with each treatment replicated either three or four times. Plant injury was evaluated one and two weeks after treat- ment using a 0 to 10 scale where 0 = no injury and 10 = complete kill. Fresh weights were taken 15 days after the application. Dry weights were also recorded. All data is presented as percent of control. Velvetleaf Study Velvetleaf were grown two plants each in 27 cm diam. plastic pots for 60 days. Individual treatments were made to plants that were 30 to 75 cm tall. The average size of the first newly expanded leaf was 36.6 sq. cm, the second newly expanded leaf was 109.7 sq. cm and the third 168.3 sq. cm. In the first experiment individual treatments were made as indicated in the general procedure. To insure that the increase in surfactant with increasing rates was not responsible for phytotoxicity, surfactant controls (Mon 0818) were applied to the top three newly expanded leaves at the levels found in a 10 and 30% solution (v/v) glyphosate. Also, to determine if an increased volume of glyphosate could compensate for lack of leaf surface .5 cc solution (v/v) was applied to the first newly expanded leaf, top two newly expanded leaves, 48 or top three newly expanded leaves at above mentioned rates. Rye Study 'Wheeler' rye was grown for 60 days in 12 cm diam. plastic pots.‘ Treatments were made as described to either the upper or under side of the leaves which averaged 8.02 sq. cm for the first newly expanded leaf and 10.6 sq. cm for either the second or third newly expanded leaf. Quackgrass Study Quackgrass rhizomes containing three nodes were planted in 12 cm diam. plastic pots. The plants were grown for 50 days, and blocked by number of plants arising from the rhizome (2 vs 3). Only one plant was treated per pot. Glyphosate was applied as previously described with the size of the first newly expanded leaf averaging 9.2 sq. cm and the second or third averaging 10.3 sq. cm. The plants were harvested 15 days after treatment for fresh weight determinations.Twenty-five days after the first harvest, a second harvest was made to determine the amount of regrowth which had occurred. 49 Results and Discussion Velvetleaf Study Application on three leaves gave significantly better kill than two leaves and both were better than one leaf (figure 1). A 1% solution of glyphosate gave significantly less kill than all other concentrations. The plants treated with this concentration did not die. Coverage of three leaves with a 1% solution did stunt velvetleaf (2/3 the size of control), but the plants were still actively growing. The interaction between leaf areas and concentrations of glyphosate on velvetleaf, shows no significant difference among three leaves, 5% solution and three leaves, 30% solution and intermediate rates in plant kill. When three leaves were treated with 5 or 10% glyphosate solution (v/v) severe stunting resulted, apical meristems were killed, but many mature leaves remained. Complete kill resulted with a 20 or 30% solution on three leaves. Seven days after plants were treated, the visual rating showed no injury from surfactant applied at the rate normally found in a 10% solution (table 1). The rate of surfactant found in a 30% solution did result in limited chlorosis on the treated leaves. At the time of harvest, the plants to which surfactant was applied were no different than those receiving 1% solutions on all three leaf areas, all rates applied to the most recently expanded 50 Fig. 1. Fresh weight reduction of velvetleaf as influenced by concentrations of glyphosate and leaf areas treated. 51 O (0 P _ID 01 (I) U) .— a :1 LL .- < < < .- (:1 [LI Ill .1 .J _l .- ,_ N on o "N in __ID ,— -O 1- pl!) :0 o - Q .- U) '_I — IHIIllllllIIIIllllIIIIIHIHHIITIIIIIIII o 0 ca =2 c2 =2 'co' -co Q N :3 (0L x 1081NOO 1N3083d ‘lHolam Hsaud GLYPHOSATE RATE, PERCENT V/V 52 TABLE 1 VELVET LEAF KILL WITH VARIOUS CONCENTRATIONS OF GLYPHOSATE AND SURFACTANT ON DIFFERENT LEAF AREAS Ratinga Conc. Treatment (%) One Leaf Two Leaves Three Leaves Glyphosate l 1.0 B 2.7 C 3.7 D 5 1.0 B 3.3 D 9.7 I 10 1.3 B 4.3 E 9.7 I 20 1.3 B 5.0 F 10.0 I 30 1.7 B 5.7 G 8.3 H Surfactant 10 --- --- 0.0 A 30 --- --- 1.0 B aMeans followed by the same letter were not significantly different at the 5% level as determined by the LSD test. 53 leaf or 5% solutions on the 2 newly expanded leaves (figure 2). In contrast to experiments where increasing volumes were applied as more leaves were treated, different results were obtained where the same volume was divided among leaves. A visual evaluation seven days after treatment showed a significant difference among three leaves, 1% solution and three leaves, 5% solution, both of which were less effective than 20 or 30% solutions (table 2). No differences were noted in any of the rates when one or two leaves were treated. A 1% concentration gave similar injury regardless of number of leaves covered. Like the initial study above, by harvest there was a significant difference in kill of velvetleaf depending on number of leaves covered (table 3). Coverage of one leaf was less effective than two and both gave less control than three leaves. A 1% concentration reduced growth only 21% while all other rates reduced growth 35 - 40% (table 4). As in the initial study 20 or 30% glyphosate solutions were needed on three leaves for complete kill.There was no interaction between number of leaves treated and concentration. In velvetleaf to prevent further growth (death of apical meristem) 9 mg of glyphosate were needed if treating two or three leaves. For complete kill plants must be treated with 36 mg on three leaves. This amount 54 Fig. 2. Fresh weight reduction of velvetleaf as influenced by concentrations of glyphosate, surfactant and leaf areas treated. 55 >\> hzmommn .m._.40 on mm on ._.._........ mp . or ........ m _ .nb- D mm>\> thomma .mh40 on ma nun- on . ...P,-. _ .__. ..tbx.. . ..). .. _ .. mw or m a!!! u 20 or 10% > 5%. Two passes with the wick applicator at all but the 5% concentration applied a greater quantity of glyphosate than one pass. Even though less injury was noted on rye with a 5% solution, two weeks after treatment there was no signi- ficant difference in plant weight from various rates or rOpe wicks used. Injury ratings on velvetleaf showed no differences among 5, 10, 20 and 30% solutions glypho- sate (v/v) as with rye, all rates of glyphosate reduced plant weight from control. 63 64 Introduction Velvetleaf infestations can cause serious economic losses in many crops. For example, densities of 2.5 to 10 weeds/m? in a typical field situation can reduce soybean yields 20 to 50% (15,19). Likewise, grass wind- breaks a necessity on muckland are time consuming and expensive to remove by undercutting and manual labor. Very few herbicides are available which will selectively control weed escapes or remove grass wind- breaks without injuring the crop. With the introduction of glyphosate, a non-selective herbicide, and the use of topical applicators, selective postemergence control became possible. The proof of the interest and success of the herbicide-toPical applicator combination is shown by the fact that in 1979, 10 to 12 million acres had glyphosate applied by rOpe wick applicators. In 1980, this increased to 20 million acres (22). Environmental factors such as relative humidity, soil moisture, light intensity, and temperature influence glyphosate's efficiency (4,14,36,41,43). Gallonage required for control varies between annual and perennial species. An application rate of .34 to 1.12 Kg/ha is usually needed to control annual species, while perennials require 1.12 to 4.48 Kg/ha glyphosate (acid equivalent)(1). Retention, absorption and translocation all function as factors of selectivity in foliar-applied herbicides. 65 In studies with quackgrass and Canada thistle (Cirsium arvense (L.) Scop.) radioactive glyphosate was rapidly absorbed and translocated to areas of highest metabolic activity (40). The area or concentrations needed have not been ascertained, and there are no data on retention with these applicators. The purpose of this study was to evaluate the role of pipe wick-applied glyphosate on retention as influenced by various rates and to note the effectiveness of these rates on plant injury and kill. Materials and Methods General Procedure All plants were grown in a greenhouse at 30: C - day, 20 C - night; 30 to 60% relative humidity with supple- mental metal halide lighting (16 h photoperiod) . Velvetleaf seeds were planted in 22.5 cm diam. plastic pots, and rye seeds in 12 cm diam. plastic pots filled with sand:peat:soil (1:1:1, v/v/v) potting media. Plants were surface watered. Twice a week soluble 20-20-20 fertilizer solution (Zg/l) was applied to each pot. ' . A 46 cm model of a pipe rope wick applicator (9) with 14 cm length ropes was used for all treatments. The wick ropes were either solid braid soft nylon (BN) or diamond braid polyester over acrylic (P/A). The applicator was attached to the frame of a moving belt 66 sprayer (1.6 km/h). Rates of formulated glyphosate applied were 5, 10, 20 and 30% solutions (v/v). At the time of treatment all plants were 60 days old. Velvet- leaf was 40 - 70 cm tall and rye was 25 cm. On each plant only the top 15.2 cm was treated. One and two weeks after treatment injury ratings were taken. Plants were harvested 15 days after application and dry weights were determined. Retention Study A solution containing formulated glyphosate and Hercules Kamaran red 640 dye (.4 g/L) was applied to the plants with a pipe rope wick applicator. The rates of glyphosate were the same as previously mentioned. Besides treating whole velvetleaf and rye plants, addi- tional rye plants were trimmed back to allow estimates of glyphosate retention on a single rye leaf. Immediately after application, the treated foliage was removed and washed in distilled water. Velvetleaf tissues were rinsed with 35 ml, while entire rye plants were rinsed in 200 ml and single leaves in 50 ml distilled water. All solutions were adjusted to equal volumes, and an aliquot removed for spectrophotometric analysis at 626 nm on the Beckman (DB-G) spectrophotometer. A standard curve was established for transmittance vs. mg of dye in the solution. After washing the plant, foliage surface areas were measured after which the plant 67 tissues were dried at 60 C for 48 h (rye) or 72 h (velvetleaf) and dry weights determined. The amount of glyphosate applied per plant area and per gram of dry weights was calculated. Results and Discussion With the BN rope there were no differences in mg/g dry weight glyphosate retained with increasing concentrations (table 1). The P/A rope delivered more glyphosate at the 10% rate than the 5% rate. Even though a 5% solution flows more easily than a 20 or 30% solution (11) less glyphosate is present, therefore less is applied. A 10% solution was more readily delivered throughout the wick than a 20 or 30% solution which may have made it comparable or better than the 20 or 30% solutions. The acrylic fibers in the P/A rope increase the wicking abilities of the rope (2), therefore more glyphosate can be applied. In subsequent experiments, the P/A rope was used. On a single treated rye leaf, no retention (ug/cm? leaf area or mg/g dry weight) differences were obtained among rates shown (table 2). Since the plants were trimmed back to one leaf there was limited support to the leaf, and little pressure exerted on the wick ropes. This created more variability among test plants and probably less reliable results. 68 TABLE 1 EFFECT OF TWO ROPE TYPES ON RETENTION OF PIPE WICK- APPLIED GLYPHOSATE BY RYE MEASURED IMMEDIATELY AFTER APPLICATION Glyphosate Retained (mg/g dry wt.)3 Conc. (%) BN P/A 5 9.6 A 22.8 A 10 49.8 AB 82.2 B 20 9.9 A 48.0 AB 30 29.1 AB 29.1 AB aMeans followed by the same letter were not significantly different at the 5% level as de- termined by Duncan's multiple range test. TABLE 2 RETENTION OF PIPE WICK-APPLIED GLYPHOSATE BY A SINGLE RYE LEAF MEASURED IMMEDIATELY AFTER APPLICATION Glyphosate Retaineda Conc. (%) (pg/cmz) (mg/g dry wt.) 5 72.5 17.3 10 58.0 15.7 20 713.2 233.4 30 247.5 72.0 aNo significant difference between means at the 5% level as determined by Duncan's multiple range test. 69 More glyphosate was applied with a 30% solution than any of the other rates. With P/A rope the 30% solution apparently can flow more easily. Since velvetleaf is more erect and rigid than rye it probably applies more pressure to the ropes resulting in better contact and greater chem- ical outflow at the higher rate. With two passes the order of retention of glyphosate on velvetleaf by various rates was 30%>20=10%>5% (table 3). Except at the 5% rate, two passes with the wick applied a significantly greater quanti- ty of glyphosate. In other studies, the control of peren- nials and dense weed stands was greater with two passes presumeably because of increased coverage (17,37,45). Two weeks after glyphosate was applied to rye a visual rating showed plants treated with a 5% solution were not as injured as all other rates (table 4). This agrees with the results in the retention study. Fewer mg of glyphosate were actually applied to the rye at the 5% concentration. The difference in injury was not apparent when plant weights were taken (table 5). The rye was completely dead regardless of rate or type of rope used. Seven days after treating velvetleaf with glyphosate only about 50% injury was noted, but by two weeks the plants were almost completely killed (table 4). Since kill was complete at all rates there was no difference in weights (table 5) . 70 Even though the test plants retained more mg/g glyphosate at the higher rates, a 5% solution was as effective as all others in ability to kill. TABLE 3 RETENTION OF PIPE WICK-APPLIED GLYPHOSATE BY VELVETLEAF MEASURED IMMEDIATELY AFTER APPLICATION. Glyphosate Retaineda Number of Passes Conc. (%) (ug/cmz) (mg/g dry wt.) 1 5 25 A 4.7 A 10 69 AB 13.4 A 20 43 A 9.6 A 30 165 D 33.2 B 2 5 52 A 10.9 A 10 146 CD 27.8 B 20 113 BC 30.9 B 30 271 E 55.2 C aMeans followed by the same letter within the same column were not significantly different at the 5% level as determined by Duncan's multiple range test. 71 TABLE 4 RATING OF RYE AND VELVETLEAF INJURY TWO WEEKS AFTER APPLYING GLYPHOSATE WITH THE GREENHOUSE PVC PIPE WICK Ratinga Conc. (%) Rye Velvetleaf 5 7.6 A 8.8 10 10.0 B 9.5 20 9.8 B 9.5 30 9.5 B 9.8 aMeans followed by the same letter were not significantly different at the 5% level as determined by Duncan's multiple range test. TABLE 5 APPLICATION OF GLYPHOSATE TO WHEELER RYE AND VELVETLEAF USING A GREENHOUSE PVC PIPE WICK Dry Weight (% of Control)a Rye Yelvetleaf Conc. (%) BN P/A P7A 5 15.0 11.3 39.9 10 8.1 9.5 39.7 20 15.4 8.9 36.5 30 14.8 15.4 37.5 aNo significant difference between means at the 5% level as determined by Duncan's multiple range test. 10. BIBLIOGRAPHY Anon. 1979. Herbicide Handbook. Weed Science Society Champaign, Ill. pp. 479. Anon. 1981. Improved rope for rope wicks. WSSA Newsletter 9(2):8. Baird, D. D., R. P. Upchurch, W. B. Homesley and J. E. Franz. 1971. Introduction of a new broadspectrum postemergence herbicide class with utility for herbaceous perennial weed control. Proc. North Cent. Weed Contr. Conf. 26:64-68. Bingham, S. W., J. Seguara and C. L. Foy. 1980. 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