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Crop Protection 34 (2012) 70e75

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Crop Protection

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Echinochloa species control in maize (Zea mays L.) with sulfonylurea herbicidesapplied alone and in mixtures with broadleaf herbicides

Christos A. Damalas a,*, Anastasios S. Lithourgidis b, Ilias G. Eleftherohorinos c

aDepartment of Agricultural Development, Democritus University of Thrace, 682 00 Orestiada, GreecebDepartment of Agronomy, University Farm, Aristotle University of Thessaloniki, 570 01 Thermi, Greecec Laboratory of Agronomy, Aristotle University of Thessaloniki, 541 24 Thessaloniki, Greece

a r t i c l e i n f o

Article history:Received 11 September 2011Received in revised form25 November 2011Accepted 29 November 2011

Keywords:Echinochloa oryzoidesEchinochloa phyllopogon (¼ E. oryzicola)ForamsulfuronNicosulfuronRimsulfuron

* Corresponding author. Tel.: þ30 25520 41116; faxE-mail address: damalas@mail.gr (C.A. Damalas).

0261-2194/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.cropro.2011.11.024

a b s t r a c t

Experiments were conducted to assess the control of Echinochloa oryzoides and Echinochloa phyllopogonwith rimsulfuron, nicosulfuron, and foramsulfuron applied alone or simultaneously with selectedbroadleaf herbicides (i.e. dicamba, MCPA, sulcotrione, and mesotrione) used in maize. In pot experi-ments, rimsulfuron (at 12.5 g ai/ha), nicosulfuron (at 40 g ai/ha), and foramsulfuron (at 45 g ai/ha)applied at the three- to four-leaf growth stage provided on average 88, 94, and 82% control of E. oryzoidesand 81, 88, and 76% control of E. phyllopogon, respectively. The average control provided by rimsulfuron,nicosulfuron, and foramsulfuron at the four- to five-leaf growth stage was 76, 81, and 71% of E. oryzoidesand 66, 82, and 62% of E. phyllopogon, respectively. Greatest control of both species at any growth stagewas observed with nicosulfuron followed by the highest dose of rimsulfuron or the highest dose offoramsulfuron. Co-application of dicamba or MCPA with each sulfonylurea herbicide provided lowercontrol of both grasses at any growth stage than the sulfonylurea alone. The addition of sulcotrione to themixtures improved the efficacy of rimsulfuron and foramsulfuron on both species at any growth stage,whereas mesotrione did not affect the efficacy of the sulfonylureas on E. oryzoides and E. phyllopogon inmost of the cases. Field experiments with the same herbicide treatments applied at the late growth stageof the two species (beginning of tillering) showed the same behavior to that observed in the pot studiesregarding the efficacy of the mixtures in most of the cases, but the reduced efficacy of the treatmentspointed out the necessity of the timely application of all sulfonylurea herbicides for effective control ofboth species. All herbicide treatments resulted in grain yield equal to that of the weed-free controlwithout any visible symptoms of toxicity or stunted growth on maize plants.

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1. Introduction

The genus Echinochloa includes about 50 species that arewidespread in both tropical and temperate regions of the world indry or water-flooded soils (Michael, 1983). Some of these speciesare considered to be among the most troublesome weeds in ricepaddy fields (Ferrero et al., 2002), whereas others are commonweeds in summer crops such as maize, cotton, soybeans, tobacco,and sugarbeets. Most species of the genus Echinochloa showa remarkable variability in several morphological and physiologicalfeatures. For example, Echinochloa plants may have erect or pros-trate bearing and also the panicles can be almost erect or noddingin variable degree with open pyramidal or closed columnar shape

: þ30 25520 41191.

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varying largely in colour from deep purple to pale green (Damalaset al., 2008). There is also variability in some physiological featuressuch as the growth rate and the time of panicle emergence whichpromotes the adaptability of these species to different environ-ments (Damalas et al., 2008).

Susceptibility to herbicides can vary among genotypes (Espebyet al., 2011) and the differential response of weed species toherbicide applications has important implications for weedmanagement. Increase of species that are difficult to control withherbicides often causes great concerns to farmers. Knowledge ofthe response to herbicides is important for the development ofeffective control strategies, particularly for Echinochloa species. Thepresence of mixed populations of these species in a field can causedifficulties in the successful chemical control because of differencesin plant traits, including germination rate, tillering ability, growthrate, and also sensitivity to herbicides (Damalas et al., 2008). Thus,information on the susceptibility of various Echinochloa species to

C.A. Damalas et al. / Crop Protection 34 (2012) 70e75 71

herbicides coupled with knowledge of the presence and populationstructure in the field is essential for the implementation ofappropriate weed control measures in certain crops or rotations,where different herbicides are usually registered. Furthermore,knowledge of the response to herbicides may provide usefulinformation for understanding shifts of the relative abundance ofthe Echinochloa weed species or populations.

Although Echinochloa oryzoides (Ard.) Fritsch and Echinochloaphyllopogon (Stapf.) Koss (¼ Echinochloa oryzicola Vasing.) aremostly weeds of rice fields, they can also occur in maize fields,particularly where maize follows rice in rotation. It is worthmentioning that 80% of the rice area in the past in Greece was inrotation with maize, sugarbeets, or cotton (Ntanos, 1998). In therecent years, although only 25% of the rice in Greece is grown inrotation, these spring crops usually follow rice in rotation (I.G.Eleftherohorinos, unpublished data). Similarly, in California 30% ofthe rice area is grown in rotationwith winter cereals, maize, cotton,sugarbeets, safflower, and vegetable crops, depending on soil andother land conditions (Hill et al., 2008). In this case, control of thesegrasses inmaize can be a problem.Weed control inmaize is of greatimportance because can reduce weed competition and thus mini-mize yield losses, protect silage feed quality, restrict weed seedproduction (by not allowing weeds to set seed in the field) and thusreduce contribution to the weed seedbank for the following crops.

Rimsulfuron, nicosulfuron, and foramsulfuron are members ofthe sulfonylurea family that are used for postemergence control ofgrass weeds and some broadleaf weeds in maize (Prostko et al.,2006; Torma et al., 2006; Nurse et al., 2007). These herbicides actthrough inhibition of the enzyme acetolactate synthase also knownas acetohydroxy acid synthase (ALS or AHAS; EC 4.1.3.18), whichcatalyzes key reactions in the biosynthesis of basic branched-chainamino acids that are essential components of the growth process inplant cell division such as valine, leucine, and isoleucine (Zhouet al., 2007). These sulfonylurea herbicides are registered forthe control of grasses in maize in Greece, including Echinochloacrus-galli, whereas there is no mention on the label about thecontrol of E. oryzoides and E. phyllopogon.

The activity of rimsulfuron, nicosulfuron, and foramsulfuron hasnot been evaluated for the control of E. oryzoides and E. phyllopogon,though these species can be a problem when maize follows rice.From this perspective, it would be interesting to see how thesegrasses respond to common herbicides of maize when appliedalone or in combinations. Mixtures of two or more herbicides area common practice for broadening spectrum of weed control andalso for reducing application costs (Damalas, 2004). Thus, theobjective of this research was a) to evaluate the control ofE. oryzoides and E. phyllopogonwith rimsulfuron, nicosulfuron, andforamsulfuron applied alone and b) to evaluate the efficacy of themixtures of these sulfonylurea herbicides with broadleaf herbicidesused in maize.

2. Materials and methods

2.1. General procedures

Seeds of E. oryzoides and E. phyllopogon were collected by handfrom mature plants growing in rice fields of the rural area of The-ssaloniki in northern Greece. Seeds were collected at the time ofnatural dispersal and only seeds that fell off carefully shaken plantswere used. Distinction of the two Echinochloa species was basedmainly on traits such as the morphology of the inflorescenceaccording to Carretero (1981) and also the time of flowering in ricefields. Nonetheless, the classification of Echinochloa species isdifficult because of the existence of numerous intergrading poly-morphic complexes with many subspecies and varieties which

often lack conspicuous identification characters. After collection,seeds were dried in the greenhouse, air-cleaned to removenon-viable seeds and waste materials, and stored in plastic bags at5e6 �C (in a refrigerator) until the initiation of the experiments.

2.2. Pot experiments

Seeds of E. oryzoides and E. phyllopogonwere planted inMay 2007and 2008 in 2-L plastic pots (13.5 cm diameter by 15.5 cm height)filledwith a soilmixture (soil and sand 2:1 v/v). The physicochemicalcharacteristics of the soil used in the experiments were clay 32%, silt56%, sand 12% (silty clay loam), organic matter 1.6%, CaCO3 7.4%, pH(1:1H2O) 7.6 and cation exchange capacity 27.7meq/100 g. Potswereplaced outdoors andwatered once daily throughout the experimentsby irrigating to soil saturation. One week after seedling emergence,plants were thinned to 20 per pot, where necessary, to obtaina uniform plant population in all pots. Plants grew normallythroughout the studies without experiencing any particular envi-ronmental stress conditions. Weather in the period of the potexperiments for 2007 was: mean air temperature 28.4 �C, meanrelative humidity 53.6%, and total precipitation 9.2 mm, whereas therespective values for 2008 were 26.5 �C, 54.5%, and 43.4 mm.

Two experiments were conducted in pots. In the first potexperiment, rimsulfuron, nicosulfuron, and foramsulfuron wereapplied alone at three application doses, i.e. 12.5,15, and 17.5 g ai/hafor rimsulfuron, 40, 50, and 60 g ai/ha for nicosulfuron, and 45, 52,and 59 g ai/ha for foramsulfuron when the two species were at thethree- to four-leaf and at the four- to five-leaf growth stages. In thesecond experiment, rimsulfuron, nicosulfuron, and foramsulfuronwere applied alone at 12.5, 40, and 45 g ai/ha, respectively, and inmixture with dicamba at 288 g ai/ha, MCPA at 600 g ai/ha, sulco-trione at 450 g ai/ha, or mesotrione at 75 g ai/ha at the three- tofour-leaf and at the four- to five-leaf growth stages. The formula-tions of the sulfonylurea herbicides were: water dispersible gran-ules (WG) for rimsulfuron, suspension concentrate (SC) fornicosulfuron, and oil dispersion (OD) with a safener (isoxadifen-ethyl at 2.25% w/v) for foramsulfuron. The specific formulations arethe only commercially available for these active ingredients inGreece. Application doses were based on the recommended dosesof the label of each product for maize. In both experiments, alltreatments of rimsulfuron were applied with the addition ofa nonionic surfactant (90% isodecyl alcohol ethoxylate) at 0.1% (v/v)according to the label. All the other herbicides did not require theaddition of an adjuvant at application. A non-treated control wasincluded for each growth stage in both experiments for compari-sons. The experiments were arranged in a completely randomizeddesign with four replications (pots) for each treatment. Herbicidetreatments were applied with a propane-pressurized hand-heldfield plot sprayer at 250 kPa pressure using 300 L/ha of water. Bothexperiments were repeated in time (two growing seasons)following the same procedure. Environmental conditions duringapplications were similar in both study periods.

Each Echinochloa species was evaluated by determining freshweight of surviving plants at 45 days after herbicide treatments.Completely desiccated plants were not included in the measure-ments. Fresh weight data were expressed as a percent reductionfrom the non-treated control (fresh weight suppression over thenon-treated control) and subjected to analysis of variance (ANOVA)separately for each species and each growth stage. In particular, forthe first experiment a 3 by 3 factorial approach (3 sulfonylureas by3 application doses) was used and for the second experiment a 3 by5 factorial approach (3 sulfonylureas by 5 mixture treatments) wasused. Before the ANOVA, the fresh weight data werelog-transformed to stabilize variance. Transformation did not affectmean separation and data interpretation; thus, the original means

Table 1Control of E. oryzoides and E. phyllopogon with rimsulfuron, nicosulfuron, and for-amsulfuron as affected by application rate (pot experiments).

Treatment Rate(g ai/ha)

Fresh weight reductiona

E. oryzoides E. phyllopogon

2007 2008 2007 2008

Growth stage 3e4 leavesRimsulfuron 12.5 91 c 85 d 83 de 79 deRimsulfuron 15.0 93 bc 87 cd 88 cd 84 cdRimsulfuron 17.5 100 a 96 a 94 abc 90 bNicosulfuron 40.0 96 ab 92 b 89 bcd 87 bcNicosulfuron 50.0 100 a 100 a 96 ab 92 abNicosulfuron 60.0 100 a 100 a 100 a 96 aForamsulfuron 45.0 84 d 80 e 76 e 76 eForamsulfuron 52.0 90 c 86 d 83 de 83 cdForamsulfuron 59.0 94 bc 90 bc 89 bcd 87 bcGrowth stage 4e5 leavesRimsulfuron 12.5 78 de 74 cd 68 cd 64 eRimsulfuron 15.0 82 cd 78 c 75 c 70 dRimsulfuron 17.5 90 b 86 b 83 b 79 bcNicosulfuron 40.0 83 c 79 c 84 b 80 bcNicosulfuron 50.0 98 a 93 a 88 ab 84 abNicosulfuron 60.0 100 a 96 a 94 a 89 aForamsulfuron 45.0 73 e 69 d 63 d 61 eForamsulfuron 52.0 81 cd 77 c 73 c 69 dForamsulfuron 59.0 89 b 85 b 82 b 78 c

a Different letters within each column in each growth stage indicate statisticallysignificant differences at P ¼ 0.05.

Table 2Control of E. oryzoides and E. phyllopogon with rimsulfuron, nicosulfuron, and for-amsulfuron as affected by partner broadleaf herbicide (pot experiments).

Treatmenta Rate(g ai/ha)

Fresh weight reductionb

E. oryzoides E. phyllopogon

2007 2008 2007 2008

Growth stage 3e4 leavesRimsulfuron 12.5 91 de 85 e 83 de 79 cde(þ) dicamba (þ) 288 80 g 76 h 70 g 68 f(þ) MCPA (þ) 600 81 g 77 gh 73 fg 71 f(þ) sulcotrione (þ) 450 98 ab 94 ab 89 abc 85 ab(þ) mesotrione (þ) 75 92 cd 87 de 84 cd 80 bcde

Nicosulfuron 40 96 abc 92 bc 89 abc 87 a(þ) dicamba (þ) 288 92 cd 87 de 83 d 80 bcde(þ) MCPA (þ) 600 94 bcd 90 cd 86 bcd 82 abcd(þ) sulcotrione (þ) 450 100 a 96 a 92 a 88 a(þ) mesotrione (þ) 75 97 ab 93 abc 91 a 87 a

Foramsulfuron 45 84 fg 80 fg 76 ef 76 ef(þ) dicamba (þ) 288 69 h 63 i 56 h 60 g(þ) MCPA (þ) 600 54 i 50 j 44 i 40 h(þ) sulcotrione (þ) 450 98 ab 94 ab 90 ab 86 ab(þ) mesotrione (þ) 75 86 ef 82 ef 82 de 78 de

Growth stage 4e5 leavesRimsulfuron 12.5 78 cde 74 cde 68 ef 64 de(þ) dicamba (þ) 288 66 g 62 g 54 g 49 f(þ) MCPA (þ) 600 68 fg 63 fg 55 g 51 f(þ) sulcotrione (þ) 450 84 ab 80 ab 77 d 72 bc(þ) mesotrione (þ) 75 80 bcd 76 abcd 69 ef 64 de

Nicosulfuron 40 83 abc 79 abc 84 ab 80 ab(þ) dicamba (þ) 288 78 cde 74 cde 78 cd 74 bc(þ) MCPA (þ) 600 79 bcde 75 bcde 79 bcd 76 abc(þ) sulcotrione (þ) 450 87 a 81 a 87 a 83 a(þ) mesotrione (þ) 75 84 ab 79 abc 85 ab 81 ab

Foramsulfuron 45 73 ef 69 ef 63 f 61 e(þ) dicamba (þ) 288 55 h 51 h 44 h 40 g(þ) MCPA (þ) 600 41 i 36 i 29 i 24 h(þ) sulcotrione (þ) 450 85 ab 81 a 74 de 70 cd(þ) mesotrione (þ) 75 75 de 70 de 68 ef 64 de

a The plus sign in parenthesis denotes a mixture with the respective sulfonylureaherbicide.

b Different letters within each column in each growth stage indicate statisticallysignificant differences at P ¼ 0.05.

C.A. Damalas et al. / Crop Protection 34 (2012) 70e7572

are presented. Differences of treatment means were compared at5% level of significance using Fisher’s protected LSD test.

2.3. Field experiments

One field experiment was conducted in 2007 and repeated in2008 at the University Farm of Thessaloniki in northern Greece. Thephysicochemical characteristics of the soil were clay 32%, silt 56%,sand 12%, organic matter 1.6%, CaCO3 7.4%, pH (1:1 H2O) 7.6 and CEC27.7 milliequivalents/100 g. Pioneer Costanza F1 hybrid maize wassown in 80-cm rows at 62,500 seeds/ha in late May in bothexperiments. Nitrogen (N) and phosphorus at 200 and 100 kg/ha,respectively, were incorporated before sowing and 150 kg/ha of Nwas applied 40 d later. A randomized complete block design withthree replicates was used for each experiment. Plot size was 2.4 by5.0 m and blocks were separated by a 2-m alley. The experimentwas established on an area infested with E. oryzoides andE. phyllopogon which occurred from a seedbank that had beenestablished for studies conducted with these species in previousyears in the same area (Damalas et al., 2008). The populationdensities of E. oryzoides ranged from 8 to 22 plants per m2 with anaverage 14.8 plants (SE ¼ �0.48) for 2007 and from 6 to 18 plantsper m2 with an average 11.2 plants (SE ¼ �0.51) for 2008. Thepopulation densities of E. phyllopogon ranged from 4 to 16 plantsper m2 with an average 8.6 plants (SE¼�0.38) for 2007 and from 4to 12 plants per m2 with an average 7.8 plants (SE ¼ �0.31) for2008. The experimental area was also infested with severalbroadleaf weeds (e.g. Portulaca oleracea, Amaranthus retroflexus,Datura stramonium) and grasses (e.g. rhizome Sorghum halepense,E. crus-galli, and Setaria spp.) most of which were unevenlydistributed in the field in patches of varying size and density.However, all these weeds were manually removed from the plotsbefore the herbicide applications because their uneven distributionand the different growth stages would not allow an adequate andobjective evaluation of the herbicide efficacy on these species.

Rimsulfuron, nicosulfuron, and foramsulfuron were appliedalone at 12.5, 40, and 45 g ai/ha, respectively, and in mixture withdicamba at 288 g ai/ha, MCPA at 600 g ai/ha, sulcotrione at 450 gai/ha, or mesotrione at 75 g ai/ha. The sulfonylurea herbicides wereapplied in the same formulations with those used in the potexperiments. Application doses were based on the recommendeddoses of the label of each product for maize. At the time ofapplication, maize was at the five- to six-leaf growth stage, mostE. oryzoides plants had 1e2 tillers formed (4e5 leaves) and mostE. phyllopogon plants were at the beginning of tillering (3e4 leaves).This stage was selectedwith the purpose of assessing the efficacy ofthe sulfonylureas and the mixture treatments at the late growthstage assessed in the pot experiments and because this isthe common practice followed by the farmers. A non-treated(weedy-infested with the two Echinochloa species only) anda weed-free control treatments were also included in the experi-ments. All rimsulfuron treatments were applied with the additionof a nonionic surfactant (90% isodecyl alcohol ethoxylate) at 0.1%(v/v) according to the label. All the other herbicides did not requirethe addition of an adjuvant at application. Herbicide treatmentswere applied with a propane-pressurized hand-held field plotsprayer at 250 kPa pressure using 300 L/ha of water. Maize wasirrigated regularly throughout the growing seasons with a water-reel self-traveling sprinkler system. Other cultural practicesduring the growing season were the usual for the area.

Echinochloa species control was evaluated by counting remain-ing healthy stems at 45 d after herbicide treatments. Stems withextensive chlorosis were considered dead. Control assessmentswere carried out on the 0.8- by 5.0-m area covered by the twocentral rows of the crop. Weed control data were expressed as

C.A. Damalas et al. / Crop Protection 34 (2012) 70e75 73

a percent reduction from the non-treated control (stem suppres-sion over the non-treated control). Furthermore, maize injury wasvisually evaluated on the two central rows of each plot. At the endof the growing season, all grained ears in the two central rows ofeach plot were hand harvested and machine shelled for thedetermination of grain yield. Grain yield was expressed as kg perha. All data (weed control and grain yield) were subjected toANOVA by using two-way ANOVA separately for each growingseason with 17 treatments (3 sulfonylureas by 5 mixtures plus theweed-free and the non-treated control treatments) replicated threetimes. Before the ANOVA, weed data were square root- trans-formed, whereas grain yield data did not need transformation.Transformation of weed control data did not affect mean separationand interpretation; thus, the original means are presented. Differ-ences of treatment means were compared at the 5% level ofsignificance using Fisher’s protected LSD test.

3. Results

3.1. Pot experiments

In the first pot experiment, the highest control of bothE. oryzoides and E. phyllopogon at the early growth stage was ach-ieved with nicosulfuron or with the highest dose of rimsulfuron(Table 1). Foramsulfuron at the lowest dose consistently providedthe lowest control of E. oryzoides, whereas the lowest control ofE. phyllopogonwas observed with the lowest dose of foramsulfuron

Table 3Control of E. oryzoides and E. phyllopogon and grain yield of maize with rimsulfuron,experiments).

Treatmenta Rate (g ai/ha) Stem number reduct

E. oryzoides

2007Rimsulfuron 12.5 68 e(þ) dicamba (þ) 288 58 g(þ) MCPA (þ) 600 56 g(þ) sulcotrione (þ) 450 82 b(þ) mesotrione (þ) 75 74 d

Nicosulfuron 40 82 b(þ) dicamba (þ) 288 75 d(þ) MCPA (þ) 600 77 c(þ) sulcotrione (þ) 450 86 b(þ) mesotrione (þ) 75 82 b

Foramsulfuron 45 64 f(þ) dicamba (þ) 288 42 h(þ) MCPA (þ) 600 30 i(þ) sulcotrione (þ) 450 82 b(þ) mesotrione (þ) 75 65 f

Non-treated control e 0 jWeed-free control e 100 a2008Rimsulfuron 12.5 63 d(þ) dicamba (þ) 288 46 fg(þ) MCPA (þ) 600 50 f(þ) sulcotrione (þ) 450 73 b(þ) mesotrione (þ) 75 69 c

Nicosulfuron 40 79 b(þ) dicamba (þ) 288 67 c(þ) MCPA (þ) 600 71 b(þ) sulcotrione (þ) 450 79 b(þ) mesotrione (þ) 75 75 b

Foramsulfuron 45 54 e(þ) dicamba (þ) 288 38 g(þ) MCPA (þ) 600 21 h(þ) sulcotrione (þ) 450 67 c(þ) mesotrione (þ) 75 63 d

Non-treated control e 0 jWeed-free control e 100 a

a The plus sign in parenthesis denotes a mixture with the respective sulfonylurea herb Different letters within each column in each growing season indicate statistically sig

or the lowest dose of rimsulfuron. At the late growth stage,although the control of both species decreased, still nicosulfuronshowed the highest efficacy among the three sulfonylurea herbi-cides, whereas the maximum control of both species with rimsul-furon or foramsulfuron was achieved only by the highest dose ofthese sulfonylurea herbicides.

In the second pot experiment, addition of dicamba or MCPA tothe mixture reduced the efficacy of rimsulfuron and foramsulfuronon both species at the early growth stage, while the efficacy ofnicosulfuron was affected less and only in the mixture withdicamba (Table 2). At the late growth stage, the reduced controlwith the mixtures of dicamba or MCPA was more evident for rim-sulfuron and foramsulfuron compared with the early growth stage.On the contrary, addition of sulcotrione to the mixture increasedthe efficacy of rimsulfuron and foramsulfuron on both speciescompared with each sulfonylurea herbicide alone irrespective ofgrowth stage. Mesotrione in mixture with each sulfonylureaherbicide did not affect the control of either species compared withthe single application of each sulfonylurea herbicide at both growthstages.

3.2. Field experiments

None of the herbicide treatments produced any visible symp-toms of toxicity or stunted growth in maize plants. Nicosulfuronprovided the highest control of both species in both yearscompared with rimsulfuron and foramsulfuron (Table 3). In both

nicosulfuron, and foramsulfuron as affected by partner broadleaf herbicide (field

ionb (beginning of tillering) Grain yieldb (kg/ha)

E. phyllopogon

f 61 f 12,604 a42 h 13,365 a44 h 13,333 a

c 81 bc 13,542 ae 72 de 12,917 ac 80 bc 13,281 a

72 de 13,573 ad 75 cde 13,469 a

83 b 13,562 ac 78 bcd 13,386 a

52 g 12,240 a30 i 12,219 a25 i 12,188 a

c 68 ef 12,136 a61 f 12,292 a0 j 5677 b

100 a 13,594 a

e 45 f 11,771 a33 g 12,417 a34 g 12,396 a

c 65 bcd 12,344 ad 66 bcd 12,031 a

73 b 12,292 ad 61 cde 12,469 acd 67 bcd 12,521 a

68 bc 12,531 ac 67 bcd 11,615 af 45 f 11,406 a

22 h 11,115 a11 i 10,885 a

d 58 de 11,562 ae 55 e 11,459 a

0 j 5261 b100 a 12,552 a

bicide.nificant differences at P ¼ 0.05.

C.A. Damalas et al. / Crop Protection 34 (2012) 70e7574

years, the efficacy of rimsulfuron and foramsulfuron on bothspecies was reduced when these herbicides were applied inmixture with dicamba or MCPA. The efficacy of nicosulfuron inthese mixtures was affected less than the efficacy of rimsulfuron orforamsulfuron and only in mixture with dicamba. In both years,addition of sulcotrione to the mixture improved the efficacy ofrimsulfuron and foramsulfuron on both species compared with theefficacy of each sulfonylurea herbicide alone. Mesotrione did nothave any significant effect on the efficacy of the sulfonylureaherbicides as compared with the efficacy of each sulfonylureaherbicide alone or slightly improved the efficacy of rimsulfuron orforamsulfuron on E. phyllopogon. In all cases, grain yield was morethan double of that of the non-treated control and equal to that ofthe weed-free control (Table 3).

4. Discussion

Control of E. oryzoides and E. phyllopogon with rimsulfuron,nicosulfuron, and foramsulfuron in this study varied depending onspecies and growth stage at application. Both species were effec-tively controlled with the sulfonylurea herbicides tested whenthese herbicides were applied preferably at an early growth stage.The greatest control of E. oryzoides and E. phyllopogon at any growthstage was observed with nicosulfuron followed by the highest doseof rimsulfuron or the highest dose of foramsulfuron.

The sulfonylurea herbicides tested in this study varied consid-erably in terms of efficacy on E. oryzoides and E. phyllopogon.Similarly, in a recent study with other target species, Hennigh andAl-Khatib (2010) reported that E. crus-galli was the most suscep-tible species to rimsulfuron and nicosulfuron, whereas Digitariasanguinalis was the least susceptible species three weeks aftertreatment, confirming that the activity of these herbicides (rim-sulfuron and nicosulfuron) depends on weed species. Regardingforamsulfuron, previous research reported that effective weedcontrol in maize can be achieved with about half of the recom-mended dose of foramsulfuron without a loss in yield (Kir andDogan, 2009). However, satisfactory control of E. oryzoides andE. phyllopogon was achieved in our study only with increasedapplication doses of foramsulfuron when applied preferably at anearly growth stage. Similar results, but with different weed species,were reported by Baghestani et al. (2007) who found that for-amsulfuron was not so effective on E. crus-galli and other grasseswhen applied at reduced doses. Evidently, the efficacy of for-amsulfuron is strongly influenced by the sensitivity of each weedspecies and the herbicide doses required for 90% control of differentweed species varied between 25 and 86 g ai ha�1 (Nurse et al.,2007).

Previous research on the control of S. halepense in maize showedthat rimsulfuron applied in mixture with dicamba gave 17% lowercontrol of S. halepense than of rimsulfuron alone (Damalas andEleftherohorinos, 2001), which is in accordance with the resultsof our study regarding E. oryzoides and E. phyllopogon. Anotherresearch also showed that the co-application of mesotrione withthe sulfonylurea herbicides rimsulfuron, nicosulfuron, and for-amsulfuron had no adverse effects on the control of D. sanguinalisor Abutilon theophrasti in a controlled environment, but decreasedthe efficacy of these herbicides on Setaria viridis, Setaria glauca, andSorghum bicolor in the field experiments (Schuster et al., 2007,2008). In our study, the addition of mesotrione did not have anysignificant effect on the efficacy of the sulfonylurea herbicides onE. oryzoides and E. phyllopogon compared with the efficacy of eachsulfonylurea herbicide applied alone. Similarly, no antagonisticinteractions were observed in tank mixtures of foramsulfuron witheither topramezone or mesotrione for the control of D. sanguinalis,E. crus-galli, S. glauca, and S. viridis var. major (Kaastra et al., 2008).

Also, mixtures of nicosulfuron with mesotrione did not show anydecrease in annual grass control in maize (Skrzypczak et al., 2011).However, nicosulfuron plus rimsulfuron in mixture with certainbroadleaf herbicides resulted in poorer control of E. crus-galli, S.viridis, and Setaria faberi than the single application of nicosulfuronplus rimsulfuron (Hennigh et al., 2010).

The equal grain yield of the herbicide treatments to that of theweed-free control showed that in spite of the differences in theefficacy of the treatments, the suppression of weeds shortly afterherbicide application allowedmaize plants to grow rapidly withoutsuffering severe competition. Weeds that were unaffected orrecovered from the herbicide treatments (i.e. plants of E. oryzoidesand E. phyllopogon) did not influence grain yield at harvest. Also, itseems that the relatively slow growth rate of E. oryzoides andE. phyllopogon (Damalas et al., 2008) as compared with maizeplants is a disadvantage of these species when grown in maize,which grows rapidly under optimal conditions. The decreasingtrend of grain yield in the treatments of foramsulfuron in 2008,particularly when applied with dicamba or MCPA, could be attrib-uted to the low levels of control of both E. oryzoides andE. phyllopogon in these treatments, but overall the differences werenot significant.

Overall, data of this study indicated that E. oryzoides andE. phyllopogon can be effectively controlled in maize with singleapplications of the sulfonylurea herbicides rimsulfuron, nic-osulfuron, or foramsulfuron. The greatest control of both grasseswas observed with nicosulfuron followed in efficacy by the highestdose of rimsulfuron or the highest dose of foramsulfuron whenapplied preferably at an early growth stage. However,co-application of dicamba or MCPA with each sulfonylurea herbi-cide gave lower control of both species at any growth stage thaneach sulfonylurea herbicide alone. On the contrary, co-applicationof sulcotrione improved the efficacy of rimsulfuron and for-amsulfuron on both species at any growth stage, whereas inmost ofthe cases mesotrione did not affect significantly the efficacy of thesulfonylurea herbicides on E. oryzoides and E. phyllopogon ascompared with the single applications.

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