Response of Alfalfa, Green Onion, Dry Bulb Onion, Sugar Beet, Head Lettuce, and Carrot to Imazosulfuron Soil Residues 2 Years after Application

BioOne sees sustainable scholarly publishing as an inherently collaborative enterprise connecting authors, nonprofit publishers, academic institutions, researchlibraries, and research funders in the common goal of maximizing access to critical research.

Response of Alfalfa, Green Onion, Dry Bulb Onion, Sugar Beet, Head Lettuce, andCarrot to Imazosulfuron Soil Residues 2 Years after ApplicationAuthor(s): Joel Felix, Steven A. Fennimore, and John S. RachuySource: Weed Technology, 26(4):769-776. 2012.Published By: Weed Science Society of AmericaDOI: http://dx.doi.org/10.1614/WT-D-12-00011.1URL: http://www.bioone.org/doi/full/10.1614/WT-D-12-00011.1

BioOne (www.bioone.org) is a nonprofit, online aggregation of core research in the biological, ecological, andenvironmental sciences. BioOne provides a sustainable online platform for over 170 journals and books publishedby nonprofit societies, associations, museums, institutions, and presses.

Your use of this PDF, the BioOne Web site, and all posted and associated content indicates your acceptance ofBioOne’s Terms of Use, available at www.bioone.org/page/terms_of_use.

Usage of BioOne content is strictly limited to personal, educational, and non-commercial use. Commercial inquiriesor rights and permissions requests should be directed to the individual publisher as copyright holder.

http://dx.doi.org/10.1614/WT-D-12-00011.1

http://www.bioone.org/doi/full/10.1614/WT-D-12-00011.1

http://www.bioone.org

http://www.bioone.org/page/terms_of_use

Weed Technology 2012 26:769–776

Response of Alfalfa, Green Onion, Dry Bulb Onion, Sugar Beet, Head Lettuce,and Carrot to Imazosulfuron Soil Residues 2 Years after Application

Joel Felix, Steven A. Fennimore, and John S. Rachuy*

Field studies were conducted from 2009 to 2011 in Oregon and from 2006 to 2008 in California to evaluate the responseof various crops to imazosulfuron soil residues 91 to 731 d after application (DAA). Imazosulfuron rates applied in Oregonwere 224 or 450 g ai ha�1 PRE, sequential 224 g ha�1 PRE and POST, or 450 g ha�1 as a tank mixture with PRE appliedS-metolachlor at 1,060 g ai ha�1 followed by 224 g ha�1 POST to potato. Imazosulfuron was applied on bare ground PREat 224, 336, and 450 g ha�1 and applied sequentially at 450 g ha�1 in California. Sugar beet planted 91 to 364 and 458 to731 DAA were injured 83 to 94% and 54 to 78% among imazosulfuron rates and application timing in 2007 and 2008,respectively. Alfalfa planted 701 DAA at rates greater than 224 g ha�1 was injured, and the forage yield was reduced.Onion, spinach, carrot, and broccoli were also injured by imazosulfuron residues when planted 91 to 731 DAA, regardlessof the rate or interval before planting. Imazosulfuron applied at 224 to 450 g ha�1 458 to 731 d before planting headlettuce resulted in moderate injury that did not reduce fresh-weight yield. The results indicated that imazosulfuron residuesin the soil have the potential to injure many rotational specialty crops for 2 yr or more in soils with pH . 6.9.Nomenclature: EPTC; imazosulfuron; rimsulfuron; S-metolachlor; alfalfa, Medicago sativa L.; broccoli, Brassica oleraceaL. var. botrytis L. ‘Marathon’; carrot, Daucus carota L. ‘Bolero F’; dry bulb onion, Allium cepa L. ‘Vaquero’; green onion,Allium cepa L. cv. ‘12000; head lettuce, Lactuca sativa L. ‘Sniper’; potato, Solanum tuberosum L. ‘Ranger Russet’; spinach,Spinacia oleracea L. ‘Whale’; sugar beet, Beta vulgaris L. ‘HM91122RR’ and ‘B4430R’.Key words: Crop rotation, herbicide soil carryover, plant back, soil residues, vegetables.

Se realizaron estudios de campo de 2009 a 2011 en Oregon y de 2006 a 2008 en California para evaluar la respuesta devarios cultivos a residuos en el suelo de imazosulfuron a 91 y 731 d despues de la aplicacion (DAA). En Oregon, las dosisde imazosulfuron aplicadas a la papa fueron 224 o 450 g ai ha�1 PRE, aplicaciones secuenciales de 224 g ha�1 PRE yPOST, o 450 g ha�1 en mezcla en tanque con S-metolachlor a 1060 g ai ha�1 PRE seguido de 224 g ha�1 POST. EnCalifornia, imazosulfuron se aplico PRE sobre suelo desnudo a 224, 336 y 450 g ha�1 y secuencialmente a 450 g ha�1. Laremolacha azucarera sembrada 91 a 364 y 458 a 731 DAA fue danada 83 a 94% y 54 a 78% en las diferentes dosis ymomentos de aplicacion de imazosulfuron en 2007 y 2008, respectivamente. Alfalfa sembrada 701 DAA a dosis mayores a224 g ha�1 sufrio dano y el rendimiento del forraje se redujo. Cebolla, espinaca, zanahoria y brocoli tambien sufrierondanos debido a los residuos de imazosulfuron, cuando se sembraron 91 a 731 DAA, independientemente de la dosis ointervalo de tiempo antes de la siembra. Imazosulfuron aplicado de 224 a 450 g ha�1, 458 a 731 d antes de la siembra delechuga, resulto en dano moderado que no redujo el rendimiento de peso fresco. Los resultados indicaron que los residuosde imazosulfuron en el suelo tienen el potencial de danar muchos cultivos rotacionales de vegetales por 2 anos o mas ensuelos con pH .6.9.

There are relatively fewer herbicides registered for weedmanagement in many specialty crops, compared withagronomic crops. Consequently, growers often take advantageof this wider array of herbicides available for use in agronomiccrops grown in rotation to manage weed species that aredifficult to control during vegetable production. Response ofvegetable crops to herbicide soil residues applied in previousyears varies (Felix, 2011; Felix and Doohan 2005; Greenland2003; Johnson et al. 2010; Robinson 2008; Soltani et al.2005). The herbicide imazosulfuron is being evaluated forpossible registration and use to control yellow nutsedge(Cyperus esculentus L.) in several crops. Imazosulfuron belongsto the sulfonylurea herbicide group (group 2–acetolactatesynthase inhibitor) that controls weeds at low application rates

and has high selectivity and low mammalian toxicity (Hay1990; Morrica et al. 2001b). Imazosulfuron propertiesinclude a molecular weight of 412.8, a pKa of 4, octanol-water partition coefficient (Kow) of 1.12 (pH 7, 25 C), and itssolubility in water is 308 mg L�1 (pH 7, 25 C)(Senseman2007). Injury in susceptible plants is characterized by stuntingand chlorosis, followed by necrosis of meristematic tissue.

Imazosulfuron is currently registered for control of manyannual and perennial broadleaf weeds and sedges in paddy rice(Oryza sativa L.) at 75 to 95 g ai ha�1 and in turf at 500 to1,000 g ha�1 (Tomlin 1997). Morrica et al. (2001b) reportedthat, when applied to the soil, imazosulfuron degradesaerobically to 2-chloroimidazo[1,2-a]pyridine-3-sulfonamideand 1-(2-chloroimidazol chloroimidazol[1,2-a]pyridine-3-yl-sulfonyl)-3-(4-hydroxy-6-methoxypyrimidin-2-yl)urea,whereas, anaerobic conditions produce 2-amino-4,6-dime-thoxypyrimidine, suggesting that degradation was due tomicroorganisms, which have the ability to demethylateimazosulfuron. In aerobic and anaerobic conditions, imazo-

DOI: 10.1614/WT-D-12-00011.1* Assistant Professor, Oregon State University/Malheur Experiment

Station, 595 Onion Ave, Ontario, OR, 97914; Extension Weed Specialist,University of California, Davis, Salinas, CA, 93905; Staff Research Associate,University of California, Davis, Salinas, CA 93905. Corresponding author’sE-mail: [email protected]

Felix et al.: Response of various crops to imazosulfuron soil residues � 769

sulfuron dissipated from the soil with a half-life ofapproximately 70 and 4 d, respectively.

Several studies have been conducted to evaluate thesuitability of imazosulfuron for weed control in various crops.Boydston and Felix (2008) reported yellow nutsedge controlwith imazosulfuron in potato. There was no effect on fresh-market tomato (Solanum lycopersicum L.) fruit shape and timeto maturity when imazosulfuron was applied POST-directedat rates ranging from 40 to 330 g ha�1 in North Carolina(Jennings 2010). Other field studies in North Carolinaindicated 10% injury to bell pepper (Capsicum annuum L.)with no reduction in yield when imazosulfuron was appliedPOST-directed at rates ranging from 56 to 448 g ha�1

(Pekarek 2009). However, Dittmar et al. (2010) reported30% injury to watermelon [Citrullus lanatus (Thunb.)Matsum. and Nakai] when imazosulfuron was applied at400 g ha�1. Recently, field studies conducted in Oregon andWashington have documented imazosulfuron efficacy onyellow nutsedge and potato tolerance when applied at ratesranging from 336 to 560 g ha�1 alone or sequentially (Felixand Boydston 2010). However, Felix (2011) reported severeinjury to dry bulb onion and sugar beet planted subsequent topotato treated with imazosulfuron, whereas dry pinto bean(Phaseolus vulgaris L.) planted 1 yr after application wastolerant.

Therefore, the objective of these studies was to evaluate theresponse of alfalfa, green onion, direct-seeded dry bulb onion,sugar beet, broccoli, head lettuce, carrot, and spinach toimazosulfuron soil residues 91 to 731 d after application.These rotational crops are representative of specialty cropsgrown in Oregon and California.

Materials and Methods

Field studies were conducted from 2009 to 2011 at theMalheur Experiment Station, Ontario, OR, and from 2006 to2008 at the U.S. Department of Agriculture–AgriculturalResearch Service/University of California Cooperative Exten-sion (USDA-ARS/UCCE) Hartnell Research Farm, Salinas,CA, to evaluate rotational crop response to imazosulfuron(League, 75% WDG, Valent U.S.A. Corporation, P.O. Box8025, Walnut Creek, CA 94596) soil residues when plantedat variable intervals following herbicide application. Herbiciderates and the intervals from application to planting ofrotational crops at each site are presented in Table 1.

Studies at the Malheur Experiment Station. Methods forstudies at the Malheur Experiment Station are presented inFelix (2011). Briefly, three studies were established in 2009,and imazosulfuron treatments were applied to control weedsin potato. The predominant soil in the three fields at theMalheur Experiment Station was an Owyhee silt loam(coarse-silty, mixed, mesic, Xerollic Camborthids), composedof 15% sand, 68% silt, 17% clay, with 1.9%, organic matter;17% sand, 67% silt, 16% clay with 1.9% organic matter; and14% sand, 68% silt, 18% clay, with 1.2% organic matter,respectively. The respective soil pH for the three fields was6.9, 7.8, and 7.9. The fields represented typical potatoproduction soils in the Treasure Valley of eastern Oregon.

The responses of dry bulb onion, sugar beet, and pinto beanto imazosulfuron soil residues were evaluated in 2010 (Felix2011). Studies followed a randomized complete-block designin 2009 and split-plot in 2010 and 2011 with threereplications. The main plots were 6.6 m wide by 9.1 m longand wide enough to accommodate three rotational crops each.Primary tillage in 2009 was completed according to localpotato production practices. Fertilization, other pest control,and irrigation followed standard potato production practicesin the western states (Strand 2006). Imazosulfuron wasapplied in 2009 at the rates indicated in Table 1. Allimazosulfuron POST application treatments included meth-ylated seed oil (MSO) at 1% (v/v), whereas rimsulfuron(Matrix, 25% WDG, E. I. du Pont Nemours and Company,Wilmington, DE 19898) included a nonionic surfactant at0.25% v/v spray solution. The herbicides were applied in atotal spray volume of 187 L ha�1 on May 18 and June 9,2009, PRE and POST, respectively. Herbicides were appliedwith a compressed CO2 backpack sprayer (CO2 SprayersSystems, Bellspray Inc., R&D Sprayers, P.O. Box 267,Opelousas, LA 70571) and a boom equipped with six TeeJet8002 EVS (flat-fan nozzle tips, Spraying Systems Co., P.O.Box 7900, Wheaton, IL 60189-7900) operated at 241 kPa.

The 2011 Cropping Season at the Malheur ExperimentStation. Immediately after harvesting the rotational crops in2010, the study area was disked twice at 15 cm depth parallelto the beds while being careful not to mix the soil amongtreatments. Shallow disking tends to dilute herbicide residuesand enhance degradation less than moldboard plowing (Felixand Doohan 2005). The beds were formed on November 19,2010, on 55 cm spacing to facilitate furrow irrigation ofrotational crops in 2011. The beds were lightly harrowedagain during spring 2011 to control emerged weeds beforeplanting rotational crops. Direct-seeded dry bulb onionvariety ‘Vaquero’ was seeded on April 8, 2011 (690 d afterherbicide application), using a precision planter to plantdouble rows spaced 10 cm apart and 9 cm within the row oneach bed. Transgenic sugar beet variety ‘Beta 27RR200 andalfalfa ‘Treasure Valley blend’ (‘VerneEmma’ þ ‘Surpass’ þ‘Perry’) was planted on April 19, 2011 (701 d after herbicideapplication). Sugar beet was planted using tractor-mountedflexi-planter units with double-disc furrow openers and coneseeders fed from a spinner divider that uniformly distributedthe seeds at 12.7 cm within the row (143,164 seeds ha�1).Alfalfa was broadcast seeded at 22 kg ha�1. The plot size foreach rotational crop was 2.2 m wide (four beds) by 9.1 mlong. Alfalfa, dry bulb onion, and sugar beet were planted in2011 following pinto bean, sugar beet, and dry bulb onion,respectively. No herbicides were used to control weeds in2011. Instead, plots were periodically hand-weeded to keeprotational crops weed free. Fertilization and other cropprotection activities followed standard local practices.

Study Irrigation and Data Collection at the MalheurExperiment Station. Plots were sprinkler irrigated in 2009,furrow irrigated in 2010 (Felix 2011), and furrow irrigated in2011, starting May 6. The monthly rainfall totals andirrigation water are presented in Table 2. Each study site wasirrigated 13 times during the 2011 season, with each event

770 � Weed Technology 26, October–December 2012

delivering approximately 10 cm of irrigation water. Fieldirrigation was scheduled based on Watermark sensor readings(Model 200SS, Irrometer moisture sensors, Irrometer Com-pany, Inc., P.O. Box 2424, Riverside, CA 92516) to preventthe soil at the 20 cm depth from drying beyond 60 kPa soil-water tension.

Sugar beet plants were evaluated for visible injury 7 and 42d after emergence (DAE), based on a scale of 0% (no apparentobservable injury) to 100% (total plant death). The height ofdry bulb onion plants was determined on June 13 and July19, 2011 (66 and 72 DAP) by measuring 10 randomly chosenplants from the ground level to the tip of the top most fullyexpanded leaf in each plot. Alfalfa height was determined onJune 13, 2011 (55 DAP), by measuring 10 randomly chosenplants from the ground to the tip of the plant in each plot. Asickle bar mower was used to harvest alfalfa on July 18 andOctober 12, 2011 (90 and 176 DAP), from the center two

rows of each plot, and the alfalfa was dried and weighed todetermine forage yield. Onion was lifted on September 12and left on the ground to cure until September 16, whenbulbs were handpicked from 4.6 m of the two center rows todetermine yield. Onion bulbs were graded on September 22to determine the marketable yield following USDA standards(USDA 1995). Sugar beet roots were harvested by hand onOctober 17, 2011, from 3 m of the two center rows; they wereweighed, and the percentage of sucrose was determined by alocal processor. Sugar beet leaves, including the root crownsfrom plants in the harvest area of each plot, were collected inpaper bags, placed in a drier for 48 h, and weighed todetermine the vegetative biomass.

Studies at Salinas, CA. The predominant soil was a Chualarsandy loam (fine-loamy, mixed, superactive, thermic TypicArgixerolls), composed of 53% sand, 32% silt, and 15% clay,with a pH 7 and 2.1% organic matter. The study was

Table 1. Herbicides, rates, and time of application before planting rotational crops.

Herbicide Rate Application date Intervala

g ai ha�1 dOntario, OR

Imazosulfuron 224 May 18, 2009 690 or 701450 May 18, 2009 690 or 701224; 224 May 18, 2009; June 9, 2009 690 or 701

S-metolachlor þ imazosulfuron; imazosulfuron 1,060 þ 450; 224 May 18, 2009; June 9, 2009 690 or 701EPTC þ pendimethalin þ S-metolachlor 4,400 þ 840 þ 1,060 May 18, 2009 690 or 701Untreated — — 690 or 701

Salinas, CAImazosulfuron 224 June 23, 2006 364 731

336 364 731450 364 731

Imazosulfuron; imazosulfuron 450; 450 June 23, 2006; December 20, 2006 364 731Imazosulfuron 224 September 22, 2006 273 640

336 273 640450 273 640

Imazosulfuron 224 December 20, 2006 184 551336 184 551450 184 551

Imazosulfuron 224 March 23, 2007 91 458336 91 458450 91 458

a Rotational crops were planted at the Malheur Experiment Station, Ontario, OR, in 2011 at 690 d after herbicide application for onion or 701 d after herbicideapplication for alfalfa and sugar beet. At Salinas, CA, crops were planted in 2007 at 91, 184, 273, or 364 d after herbicide application and in 2008 at 458, 551, 640 or731 d after herbicide application.

Table 2. Total rainfall and irrigation amountsa for Ontario, OR (2009 to 2011), and Salinas, CA (2006 to 2008).

Year January–April May June July August September October–December Total

mmOntario, OR

2009 53 59 113 167 102 64 94 6512010 130 132 151 305 428 106 164 1,4162011 122 165 320 410 501 — — 1,518

Salinas, CA2006 — — 29 77 42 85 175 4082007 138 79 102 123 127 62 68 6992008 152 0 150 188 131 42 — 663

a Rainfall records for Ontario, OR, were obtained from the Malheur experiment station about 1 km from the study site. Crops at the Malheur Experiment Station weresprinkler-irrigated in 2009. Crops were furrow-irrigated in 2011 for 24 h per occurrence (water inflow was estimated to be 100 mm). Furrow irrigation was scheduled tomaintain moisture in the top 20 cm of the soil profile. At Salinas, CA, records were obtained from the weather station at Salinas Municipal Airport, located about 1.6 kmfrom the trial site. During the trial fallow periods at Salinas, CA (October to May), bare soil was sprinkler-irrigated 3 to 5 h (25 to 42 mm), one to two times duringmonths without rainfall. During the growing period (June to September), crops were sprinkler-irrigated for 0.5 to 5 h (6 to 42 mm), one to two times per week.


established in 2006 following a split-plot design, with alltreatments replicated four times. The main-plot was conven-tionally or minimally tilled, whereas the four herbicideapplication timings formed subplots, each with threeimazosulfuron rates. Each main plot also included asequential imazosulfuron at 450 g ha�1 treatment and theuntreated control. Individual plots were a single bed 2 m wideby 7.6 m long. Imazosulfuron herbicide rates and the date forapplication timing are presented in Table 1. Herbicides wereapplied using a compressed CO2 backpack sprayer and aboom (193 cm wide) equipped with four 8002VS flat-fannozzles operated at 207 kPa to deliver 374 L ha�1 of spraysolution. The study area was immediately sprinkler irrigatedwith 30 mm of water to activate the herbicide. Because nocrop was planted in the application year, maintenanceherbicides were used to keep the study area free of weeds.Glyphosate (Roundup PowerMax, Monsanto Company, 800N. Lindburgh Blvd., St. Louis, MO63167) at 2% v/v wasapplied in 206 L ha�1 on August 4, 2006, followed byglyphosate 2% v/v plus carfentrazone (Shark H2O, 40%WDG, FMC Corporation, 1735 Market St., Philadelphia,PA 19103) 16.8 g ai ha�1 in 262 L ha�1 on November 3,2006. Carfentrazone was chosen as a maintenance herbicidebecause of the effectiveness to control burning nettle (Urticaurens L.), which was prevalent in the field. Plots were treatedagain with glyphosate 4% v/v in 168 L ha�1 and 2% v/v in262 L ha�1 on November 27, 2007, and February 28, 2008,respectively. Otherwise, the plots were hand-weeded asneeded to keep the study area free of weeds throughout theduration of the study.

Study Irrigation at Salinas, CA. During the herbicideapplication period (June 23, 2006, to June 22, 2007), theplots were sprinkler irrigated immediately after each applica-tion. Between herbicide application timings, plots wereirrigated on a 4 to 6 wk schedule, unless rainfall occurred.During the 2007 and 2008 cropping seasons (June toOctober), the crops were irrigated two to three times perweek as needed. Total rainfall and irrigation amount appliedis presented in Table 2. The soil was not disturbed or givensupplemental irrigation during the period between the 2007and 2008 cropping season (October 2007 to June 2008).

The 2007 Cropping Season at Salinas, CA. The study areawas cultivated on June 20, 2007, to prepare the soil forplanting. The conventional-tillage plots were disked parallelto the beds and carefully reshaped without mixing the soilbetween beds. The minimum-tillage plots were left undis-turbed except for light cultivation using a Lilliston rollingcultivator (Lilliston Corporation, P.O. Box 3930, Albany, GA31706) to mix the soil in the top 5 to 7.5 cm, and a bedshaper used to reform the raised beds. Spinach (Whale),broccoli (Marathon), head lettuce (Sniper), sugar beet(experimental B4430R), green onion (experimental 1200),and carrot (Bolero F) were each seeded in single rows (withthe exception of spinach, which was planted in a three seed-line row) at 15-cm spacing between rows across the bed topusing a Stanhay planter on June 22, 2007. Spinach wasdamaged by birds and was replanted July 13, 2007, with thesame cultivar using a walk-behind seeder.

Crop injury (foliar phytotoxicity or plant stunting) wasevaluated similar to the procedure used at the MalheurExperiment Station. Evaluations were done on July 27, 2007,at 35 d after planting (DAP) for all crops, except spinach (14DAP). Crop plant stand and fresh weights were determined aseach crop (except spinach) was near maturity. Broccoli andsugar beet were assessed for injury on August 14 (53 DAP),head lettuce on August 17 (56 DAP), carrot on August 20 (59DAP), and green onion on September 18, 2007 (88 DAP).Fresh biomass weights were recorded for each crop in everyplot. Because of very poor/nonuniform growth of the spinachcrop, no biomass was recorded.

The 2008 Cropping Season at Salinas, CA. On June 13,2008, the entire study was irrigated to supply about 25 mm ofwater to prepare the soil for cultivation and planting. The soilin the top 2.5 to 5 cm of all beds was lightly cultivated byseveral passes of a bed-shaper on June 18, 2008. The samecrop varieties used in the previous year were planted on June23, 2008, following the same techniques as in 2007.

Crop injury was assessed using the same procedure as 2007.Spinach was evaluated on July 15, 2008 (22 DAP), broccoliand head lettuce on July 21 (28 DAP), and green onion andcarrot on August 13 (51 DAP). Crop stand and fresh biomassyields were determined following the same procedure as 2007.Broccoli was evaluated for injury on August 13 (51 DAP),sugar beet on August 15 (53 DAP), spinach on August 22 (60DAP), head lettuce on August 29 (67 DAP), carrot onSeptember 4 (73 DAP), and green onion on September 9,2008 (78 DAP).

Statistical Analysis. The data from each location weresubjected to a normality test for compliance with theassumptions for statistical analysis. Because analysis ofsquare-root–transformed data did not change the results ofANOVA, the nontransformed data were used in the finalanalysis. Data were subjected to ANOVA using PROC GLMprocedure in SAS (Version 9.2. SAS Institute, Inc., 100 SASCampus Drive, Cary, NC 27513-2414; SAS 2008). Type IIIstatistics were used to test for significant differences(P � 0.05) among herbicide treatments, studies, and theirinteractions for plant height and yield variables in 2011 atMalheur Experiment Station and 2007 and 2008 at Salinas,CA. Data were pooled among studies at Malheur Experimentstation because ANOVA indicated no significant differenceamong studies or study-by-treatment interactions. Also,because there was not much tillage effect on most variablesat Salinas, CA, only the conventional-tillage data arepresented. The ANOVA indicated significant differencebetween year, herbicide application timing, and rates atSalinas, CA, but not for the interactions. Therefore, theSalinas, CA, data are presented separately for each year,application timing, and herbicide rates. Mean separationswere performed using Fisher’s Protected LSD test at aP � 0.05.

Results and Discussion

Sugar Beet Response. Sugar beet planted at Salinas, CA, in2007 displayed extreme sensitivity to imazosulfuron soil


residues, regardless of herbicide rate or interval fromapplication to planting (Table 3). Visible injury ranged from83 to 95% for sugar beet planted 91 to 364 d afterimazosulfuron application (DAIA). Sugar beet plant stand wasreduced 45 to 100% among herbicide rates and applicationtimings relative to the untreated control (data not shown).Sugar beet planted 458 to 731 DAIA displayed injury rangingfrom 54 to 78% among imazosulfuron rates and interval fromapplication to planting (Table 3). Plant stand at 53 DAP in2008 was 0 to 7.7 plants m�1 row among herbicide rates,compared with 10.2 plants m�1 for the untreated control.Plant fresh weight reflected the level of injury (plant stunting)and plant stand, and was greatly reduced among imazosulfur-on rates and timing.

Plant stand for sugar beet planted 701 DAIA at theMalheur Experiment Station was reduced 50 to 66%,compared with the grower standard (5.8 plants m�1 of row)(Table 4). The highest reduction in plant stand was observedin soil residues resulting from imazosulfuron applied at 450 gha�1 PRE or sequential 450 g ha�1 plus S-metolachlor 1,060 gha�1 PRE followed by 224 g ha�1 POST. Sugar beet injury at7 and 42 DAE was characterized by severe stunting thatranged from 60 to 95% among herbicide treatments (data notshown). Vegetative biomass at root harvest ranged from 200to 1,500 kg ha�1 for different imazosulfuron treatmentscompared with 5,200 kg ha�1 for the grower standard and4,900 kg ha�1 for the untreated control (Table 4). Sugar beetplants in plots previously treated with imazosulfuronremained stunted and produced lower root yield. Imazosul-furon soil residues reduced the root yield 79 to 98%compared with the grower standard (105,000 kg ha�1).Sensitivity of sugar beet to imazosulfuron soil residues 365 dafter application was reported by Felix (2011). Sugar beetsensitivity to sulfonylurea herbicides has been reported byother researchers. Moyer and Esau (1996) reported sugar beetyield reductions up to 3 yr after imazethapyr application to

dry bean. Sugar beet was injured by chlorsulfuron residuesfollowing application to wheat (Triticum aestivum L.) in theprevious year (Brewster and Appleby 1983). In studies byMoyer (1995), irrigated sugar beet was greatly injured byresidues of sulfonylurea herbicides tribenuron and thifensul-furon. Novosel et al. (1995) reported increased levels of sugarbeet injury and corresponding yield loss from soil residues ofprimisulfuron herbicide applied at 40 and 80 g ha�1. Theyreported a correlation between organic matter and theadsorption of primisulfuron across soil types.

Green and Dry Bulb Onion Response. Green onion planted91 to 731 DAIA at 224 g ha�1 to 450 g ha�1 was severelyinjured by the soil residues at Salinas, CA (Table 3).Evaluations at Salinas, CA, in 2007 (35 DAP) revealed 81to 98% injury across herbicide rates for green onion planted91 to 364 DAIA. Green onion planted 458 to 730 DAIA in2008 were injured 63 to 100% across herbicide rates. Plantstand at 78 DAP in 2008 ranged from 1.2 to 12 plants m�1 ofrow across imazosulfuron rates, compared with 12.2 m�1 forthe nontreated control. Plant stand was not affected whengreen onion was planted 731 DAIA at 224 and 450 g ha�1,but plants were generally stunted. It is unclear why theresidues from imazosulfuron 336 g ha�1 were more injuriousto green onion planted 731 DAIA compared with 224 and450 g ha�1. Differential soil organic matter among plots mayhave contributed to the observed results. Novosel et al. (1995)reported a correlation between organic matter and theadsorption of primisulfuron, a sulfonylurea herbicide similarto imazosulfuron, across soil types. Plant fresh weight wasdirectly related to green onion plant stand and vigor. It isimportant to note that the plants that survived the residuesfrom 224 and 450 g ha�1 applied 731 DAIA were generallystunted and produced only 37% of the untreated controlbiomass (81.8 g m�1 row).

Dry bulb onion planted 690 DAIA at 450 g ha�1 orsequential 450 followed by 224 g ha�1, reduced the onion

Table 3. Sugar beet and green onion plant injury, plant stand, and aboveground fresh weight in response to imazosulfuron soil residues at the USDA-ARS/UCCEHartnell Research Farm, Salinas, CA, 2007 and 2008.

Imazosulfuron rate

Interval

Sugar beet Green onion

Plant injury Plant stand Fresh wt Plant injury Plant stand Fresh wt

2007 2008 2007 2008 2008 2007 2008 2008

g ai ha�1 DBPa % no. m�1 row g m�1 row % no. m�1 row g m�1 row

224 364 731 85 54 5.7 1.7 88 63 11.3 31.3336 364 731 86 71 1.3 0.3 91 90 7.1 5.9450 364 731 83 70 7.7 1.5 81 73 11.3 28.5224 273 640 93 70 0.0 0.0 89 90 5.3 1.7330 273 640 88 73 1.3 0.2 91 100 1.7 0.6450 273 640 94 75 2.5 0.5 98 96 3.8 1.6224 184 551 90 70 5.2 1.5 91 83 7.2 8.6330 184 551 94 71 2.9 0.5 98 97 1.3 0.5450 184 551 93 75 0.0 0.0 96 95 1.2 1.4224 91 458 88 68 6.5 2.0 94 80 12.0 12.3330 91 458 94 70 0.0 0.0 96 98 4.0 2.2450 91 458 93 78 3.5 0.5 99 99 2.7 0.3450; 450 364 551 93 75 1.9 0.3 94 94 2.3 1.90 — 38 0 10.2 1,256.2 36 0 12.2 81.8LSD 0.05 14 9 3.1 491.1 13 9 4.0 18.7

a Abbreviations: DBP, days before planting.


plant height and yield at the Malheur Experiment Stationcompared with the grower standard and untreated control(Table 4). Onion plant height on June 13, 2011, for the fore-mentioned rates was reduced 30% compared with the growerstandard (22 cm). Evaluations on July 19, 2011, indicatedthat onion plant height was reduced an average of 39%compared with the grower standard (55 cm). Plants growingin plots previously treated with imazosulfuron at 224 g ha�1

had similar plant height to the grower standard on bothevaluation dates.

The U.S. no. 1 bulb yield followed the pattern of plantheight response, and onion following imazosulfuron at 224 gha�1 produced similar yield as the grower standard and theuntreated control. Soil residues from imazosulfuron at 450 gha�1 and sequential 450 followed by 224 g ha�1 reduced yieldby 68 and 65%, respectively, compared with the growerstandard (62,400 kg ha�1). Onion sensitivity to sulfonylureaherbicides has been reported by other researchers. Felix (2011)reported dry bulb sensitivity to imazosulfuron soil residueswhen planted 365 d after herbicide application. Greenland(2003) reported 43% and 51% reduction in onion yield fromnicosulfuron soil residues 12 mo after application to corn (Zeamays L.) at 70 and 140 g ha�1, respectively.

Alfalfa Response. Soil residues from imazosulfuron 450 gha�1 PRE and sequential 450 g ha�1 plus S-metolachlor 1,060g ha�1 PRE followed by imazosulfuron at 224 g ha�1 POSTreduced alfalfa plant height 59% compared with the growerstandard (17 cm) (Table 4). Imazosulfuron 224 g ha�1 PRE orsequential PRE and POST applied 701 d before plantingalfalfa did not affect alfalfa height. However, there was a 32%and 59% reduction in the total alfalfa forage yield fromresidues of imazosulfuron applied sequentially at 224 g ha�1

(PRE and POST) and 450 g ha�1 PRE 701 d before plantingalfalfa, respectively. Soil residues from the combination ofimazosulfuron 450 g ha�1 plus S-metolachlor 1,060 g ha�1

PRE followed by imazosulfuron 224 g ha�1 POST reducedalfalfa yield 70% compared with the grower standard (7,600kg ha�1). Imazosulfuron at 224 g ha�1 applied 701 d beforeplanting alfalfa did not reduce forage yield.

Spinach Response. Spinach planted 91 to 731 DAIAexhibited sensitivity to soil residues of imazosulfuron appliedat 224 to 450 g ha�1 (Table 5). Injury from spinach planted91 to 364 DAIA ranged from 49 to 64% among herbiciderates. The injury subsided somewhat in 2008 (24 to 60%),when spinach was planted 458 to 731 DAIA. Injurysymptoms were generally characterized by stunted plantsregardless of the rate and the interval before planting. Spinachplant stand at 60 DAP in 2008 ranged from 0 to 120% of theuntreated control (7.5 plants m�1 of row), depending onherbicide rate and the interval from application to planting.Spinach was not harvested in 2007 because of bird damage.Spinach fresh weight in 2008 was dependent on the plantstand and ranged from 0 to 44% of the nontreated control(15.8 g m�1 of row).

Carrot Response. Imazosulfuron soil residues severely injuredcarrot planted 91 to 731 DAIA (Table 5). Carrot planted 91to 364 DAIA were injured 84 to 94% across herbicide rates(Table 5), resulting in no harvestable roots (data not shown).Carrot planted 458 to 731 DAIA resulted in 58 to 98% injuryacross herbicide rates. Imazosulfuron applied 731 d beforeplanting at 224 to 450 g ha�1 did not reduce carrot plantstand. Generally, residues from imazosulfuron at 224 g ha�1

applied 458, 551, 640, and 731 d before planting did notreduce carrot stand. However, the plants were stunted andproduced relatively lower fresh-weight yield compared withthe untreated control. Carrot fresh weight was reduced 61 to99.9% across herbicide rates, compared with the untreatedcontrol (1,190 g m�1 of row). These results contrast with thefindings by Greenland (2003) who reported no carrot injurywhen planted 12 mo after application of flumetsulam andnicosulfuron, both sulfonylurea herbicides. It is likely that theloamy-sand soil with higher organic matter may haveaccelerated herbicide degradation in that study.

Broccoli Response. Broccoli planted 91 to 364 DAIA at 224to 450 g ha�1 was injured 50 to 90% (Table 6). Plants wereseverely stunted and produced no harvestable crop at the endof the season. The injury remained high in 2008 (26 to 85%)

Table 4. Pooled yield for direct-seeded dry bulb onion, sugar beet, and alfalfa in response to imazosulfuron soil residues 690 to 701 d after application at the MalheurExperiment station, Ontario, OR, in 2009 to 2011.

Treatment Rate Timingb

Onion Sugar beet Alfalfa

Height Bulb yielda

Plantstand

Vegetativebiomass

Rootyield

Height Yield

June 13 July 19 Small U.S. no. 1 June 13 August 8 September 8 Total

g ai ha�1 cm kg ha�1 no. m�1 kg ha�1 cm 3 1,000 kg ha�1

Imazosulfuron 224 PRE 23 50 3,100 54,200 2.9 1,500 22,400 16 2.5 4.0 6.5Imazosulfuron 450 PRE 16 32 3,400 20,000 2.0 200 2,000 7 0.9 2.2 3.1Imazosulfuron 224; 224 PRE; POST 21 39 4,900 38,500 2.7 400 4,000 13 1.9 3.3 5.2S-metolachlorþ imazosulfuron

1,060 þ 450;224

PRE; POST 16 35 4,700 21,800 2.0 200 1,800 7 0.5 1.8 2.3

Grower standardc 23 55 2,700 62,400 5.8 5,200 105,000 17 2.7 4.9 7.6Nontreated 22 53 2,900 63,500 5.4 4,900 106,800 16 2.3 5.3 7.6LSD 0.05 4 7 1,100 22,800 1.1 600 8,600 4 0.9 0.9 1.3

a U.S. no. 1 onion category comprised bulbs sized �3.75 cm in diameter, without any blemishes.b Abbreviations: POST treatment included methylated seed oil at 1% v/v.c Grower standard treatment included a tank mix of EPTC plus pendimethalin plus S-metolachlor at 4,400 plus 840 plus 1,060 g ai ha�1 PRE, followed by

rimsulfuron 70 g ai ha�1 plus 0.25% v/v POST.


when broccoli was planted 458 to 731 DAIA. Soil residuesfrom imazosulfuron 224 g ha�1 did not reduce plant standwhen broccoli was planted 458 to 731 DAIA. However, theplants were severely stunted and produced lower fresh weightcompared with the nontreated control. The highest broccoliyield among imazosulfuron rates and application timings wasonly 25% of the 788.2 g m�1 of row for the untreated control.

Head Lettuce Response. Head lettuce planted 91 to 364DAIA was injured 48 to 83% across herbicide rates (Table 6).Yield for head lettuce planted 91 to 273 DAIA was greatlyreduced (173 to 804 g m�1 of row), compared with theuntreated control (1,708 g m�1) (data not shown). The injuryfor lettuce planted 458 to 731 DAIA ranged from 19 to 60%,

with sequentially applied imazosulfuron at 450 g ha�1

suffering the highest injury. Head lettuce planted 731 DAIAat 224 g ha�1 suffered the lowest injury (19%). Plant standwas generally similar across herbicide rates when lettuce wasplanted 458 to 731 DAIA. Soil residues from imazosulfuronapplied at 224 to 450 g ha�1 did not reduce fresh-weight yieldwhen head lettuce was planted 458 to 731 DAIA.

In summary, because the studies were irrigated at both sites,soil moisture, or lack thereof, can be discounted as a factor inimazosulfuron carryover in these studies. The results suggestthat soil pH may have contributed to imazosulfuroncarryover. The soil pH in the three fields at Ontario, OR,was 6.9, 7.8, and 7.9, and it was 7.0 at Salinas, CA. Morrica

Table 5. Spinach and carrot injury, plant stand, and fresh weight in response to imazosulfuron soil residues at the U.S. Department of Agriculture–AgriculturalResearch Service/University of California Cooperative Extension, Hartnell Research Farm, Salinas, CA, 2007 and 2008.

Imazosulfuron rate

Application timing

Spinach Carrot


2007 2008 2007 2008 2008 2007 2008 2008


224 364 731 56 24 9.0 6.9 85 58 16.3 465.2336 364 731 55 45 0.9 0.4 90 98 11.8 21.5450 364 731 49 43 0.0 0.0 84 78 12.0 105.5450; 450 364 551 63 55 1.0 0.3 91 93 5.2 8.9224 273 640 56 49 0.0 0.0 89 85 14.7 15.5330 273 640 63 51 5.7 1.3 84 99 7.0 5.9450 273 640 54 54 3.8 1.2 94 95 6.5 8.5224 184 551 51 48 6.3 4.1 89 85 11.9 43.0330 184 551 55 46 6.9 1.7 94 89 6.3 20.4450 184 551 56 60 0.0 0.0 94 91 7.3 15.4224 91 458 64 41 5.3 1.7 94 75 11.1 144.2330 91 458 60 45 5.0 1.2 93 93 9.0 11.9450 91 458 61 58 1.1 0.3 91 96 7.3 1.70 — 11 0 7.5 15.8 34 0 11.3 1,189.5LSD 0.05 13 10 3.5 7.5 12 11 5.6 161.2

a Abbreviations: DBP, days before planting; NA, not applicable.

Table 6. Broccoli and head lettuce foliar injury, plant stand, and fresh weight in response to imazosulfuron soil residues at the U.S. Department of Agriculture–Agricultural Research Service/University of California Cooperative Extension, Hartnell Research Farm, Salinas, CA, 2007 and 2008.

Imazosulfuron rate

Application timing

Broccoli Head lettuce


2007 2008 2007 2008 2008 2007 2008 2008


224 364 731 50 26 17.7 200.1 48 19 19.0 1,991336 364 731 74 58 16.7 71.9 56 41 19.1 2,108450 364 731 71 56 16.3 70.0 50 29 18.0 2,220450; 450 364 551 89 85 8.5 7.3 83 60 19.9 1,457224 273 640 71 65 14.7 4.4 63 40 18.7 1,664330 273 640 84 75 10.3 11.8 64 40 17.0 2,144450 273 640 85 78 16.0 21.4 74 39 19.8 2,101224 184 551 80 70 16.5 49.2 68 30 18.0 2,102330 184 551 90 80 15.5 21.8 79 39 18.7 2,206450 184 551 88 85 9.7 9.9 81 46 18.5 2,172224 91 458 85 66 13.8 50.1 68 36 18.0 2,258330 91 458 83 78 16.3 31.7 76 48 15.7 2,255450 91 458 88 80 13.3 4.7 81 44 20.2 1,6030 — 14 0 15.5 788.2 20 0 16.5 1,399LSD 0.05 11 13 7.5 175.7 14 17 3.1 NS

a Abbreviations: DBP, days before planting; NS, no significant difference.


et al. (2001a) reported that the hydrolysis rate of imazosulfur-on was characterized by a first-order kinetics, was pH- andtemperature-dependent, and was accelerated by acidic condi-tions and higher temperatures. Imazosulfuron half-lives at pH4.5 and 5.9 were reported to be 36.5 and 578 d, respectively(Morrica et al. 2001b). Additionally, previous studies havealso indicated no significant change in imazosulfuronconcentration after 150 d at soil pH 6.6, 7.4, 9.2, and 12.3(Morrica et al. 2001b; Senseman 2007). Sulfonylureaherbicides are primarily degraded by hydrolysis and microbes.Consequently, the possibility for carryover is greater in higherpH soils (pH . 6.8) because acid hydrolysis ceases at highpH levels.

These results suggest significant sensitivity of sugar beet,green and direct-seeded dry bulb onion, spinach, carrot, andbroccoli to imazosulfuron soil residues. However, head lettuceplanted 458 to 731 DAIA displayed tolerance to imazosulfur-on residues. Alfalfa was tolerant of soil residues fromimazosulfuron at 224 g ha�1 if planted 701 d afterapplication.

Imazosulfuron soil residues have the potential to injure awide range of rotational crops. Therefore, it is ourrecommendation that further work be undertaken tounderstand the safe replant intervals for vegetable crops on arange of soil types and soil pH. The findings of this researchsuggest that, until there is a better understanding of thedegradation characteristics of imazosulfuron in soil, vegetablesshould not be planted subsequent to crops treated withimazosulfuron in areas where soils have a pH greater than 6.8.

Acknowledgments

The authors thank Joey Ishida for the help with fieldactivities at the Malheur Experiment Station. The help ofmany summer workers to hand-weed and harvest crops isgreatly appreciated. We thank Valent Corporation for theirfinancial support of the research at Salinas, CA.

Literature Cited

Boydston, R. A. and J. Felix. 2008. Yellow nutsedge control in potato withimazosulfuron. Proc. West. Soc. Weed Sci. 61:6 [Abstract].

Brewster, B. D. and A. P. Appleby. 1983. Response of wheat (Triticum aestivum)and rotation crops to chlorsulfuron. Weed Sci. 31:861–865.

Dittmar, P. J., K. M. Jennings, and D. W. Monks. 2010. Response of diploidwatermelon to imazosulfuron POST. Weed Technol. 24:127–129.

Felix, J. 2011. Response of dry bulb onion, sugar beet, and pinto beans toimazosulfuron soil residues. Weed Technol. 25:586–590.

Felix, J. and R. A. Boydston. 2010. Evaluation of imazosulfuron for yellownutsedge (Cyperus esculentus) and broadleaf weed control in potato. WeedTechnol. 24:471–477.

Felix, J. and D. J. Doohan. 2005. Response of five vegetable crops to isoxaflutolesoil residues. Weed Technol. 19:391–396.

Greenland, R. G. 2003. Injury to vegetable crops from herbicides applied inprevious years. Weed Technol. 17:73–78.

Hay, J. V. 1990. Chemistry of sulfonylurea herbicides. Pestic. Sci. 29:247–261.Jennings, K. M. 2010. Tolerance of fresh-market tomato to postemergence-

directed imazosulfuron, halosulfuron, and trifloxysulfuron. Weed Technol.24:117–120.

Johnson, W. C., III, T. L. Grey, and D. Kissel. 2010. Interactive effects of soilpH, halosulfuron rate, and application method on carryover to turnip greenand cabbage. Weed Technol. 24:160–164.

Morrica, P., F. Barbato, I. R. Della, S. Seccia, and F. Ungaro. 2001a. Kineticsand mechanism of imazosulfuron hydrolysis. J. Agric. Food Chem. 49:3816–3820.

Morrica, P., A. Giordano, S. Seccia, F. Ungaro, and M. Ventriglia. 2001b.Degradation of imazosulfuron in soil. Pest Manag. Sci. 57:360–365.

Moyer, J. R. 1995. Sulfonylurea herbicide effects on following crops. WeedTechnol. 9:373–379.

Moyer, J. R. and R. Esau. 1996. Imidazolinone herbicide effects on followingrotational crops in southern Alberta. Weed Technol. 10:100–106.

Novosel, K. M., K. A. Renner, J. J. Kells, and A. J. Chomas. 1995. Sugarbeet(Beta vulgaris) response to and sorption characteristics of nicosulfuron andprimisulfuron. Weed Technol. 9:484–489.

Pekarek, R. 2009. Evaluation of a ‘Caliente’ Mustard Cover Crop, S-Metolachlor,Imazosulfuron, and Thifensulfuron-Methyl for Weed Control in Bell Pepper.Ph.D dissertation. Raleigh, NC: North Carolina State University. 129 p.

Robinson, D. E. 2008. Atrazine accentuates carryover injury from mesotrione invegetable crops. Weed Technol. 22:641–645.

Senseman, S. A., ed. 2007. Herbicide Handbook. 9th ed. Lawrence, KS: WeedScience Society of America. Pp 91–92.

Soltani, N., P. H. Sikkema, and D. E. Robinson. 2005. Effect of foramsulfuronand isoxaflutole residues on rotational vegetable crops. Hortscience 40:620–622.

Strand, L. 2006. Integrated pest management for potatoes in the western UnitedStates 2nd ed. Davis, CA: University of California Statewide Integrated PestManagement Program. Pub. 3316. 167 pp.

Tomlin, C. D. C. 1997. The Pesticide Manual. 11th ed. Farnham, Surrey, UK:British Crop Protection Council. Pp. 703–704.

[USDA] U.S. Department of Agriculture. 1995. United States Standards forGrades of Onions (Other than Bermuda-Granex-Grano and Creole Type).Washington, DC: Agricultural Marketing Service. 9 p. http://www.ams.usda.gov/AMSv1.0/getfile?dDocName¼STELPRDC5050312. Accessed: April 27,2012.

Received January 22, 2012, and approved July 22, 2012.


Documents

Response of Alfalfa, Green Onion, Dry Bulb Onion, Sugar Beet, Head Lettuce, and Carrot to Imazosulfuron Soil Residues 2 Years after Application