Application of pre-emergence herbicides in poplar nursery production

Verica Vasic?Sasa Orlovic?Predrag Pap?Branislav Kovacevic?Milan Drekic?Leopold Poljakovic Pajnik?Zoran Galic

Application of pre-emergence herbicides in poplar nursery production

Verica Vasic?Sasa Orlovic?Predrag Pap?Branislav Kovacevic?Milan Drekic?Leopold Poljakovic Pajnik?Zoran Galic

In addition to pests and diseases,weeds are a major problem in poplar nursery production.The possibilities ofherbicide application in juvenile poplargrowth were researched,taking into account that weeds are one of the main limiting factors.The following pre-emergence herbicides were tested:acetochlor,S-metolachlor,metribuzin, oxifluorfen,and dimethenamid during two vegetation seasons at two locations,which differed by the soil physicochemical characteristics.The study results show that the number of weeds on sample plots was significantly reduced by the tested herbicides when compared to controlplots.The highestreduction in thenumberofweedswasachieved using the herbicides acetochlor and metribuzin.However,metribuzin showed a phytotoxic effecton sandy soil.Metribuzin application isrecommended only on the soilswith higher contents oforganic matter,where the phytotoxic effectwas absent.Acetochlor,S-metolachlor,oxifluorfen,and dimethenamid were notphytotoxic to poplars and can be used for weed suppression in the production of poplar plants.

Poplar,weedsWeed managementHerbicidesPhytotoxic effects

Introduction

Nursery production of poplar plants is defined as intensive plant production consisting of strict application of prescribed treatments during the entire production process.In addition to insectpestsand diseases,greatproblem in poplar nursery production are weeds.Thanks to wide inter-row distances and open canopy during the early stages of plant development,poplarnurseries are idealplacesforexpansion of numerous weeds(Vasic et al.2007).The life space of juvenile forest plants is invaded,they are shadowed and choked,and theirwaterand nutrientsaretaken(Wagneretal. 2006;Kabba etal.2007;Tobisch 2007).Marino and Gross (1998)report that abundant weeds can affect poplar morphologicaltraits,leading to shorterplants,with smallerbasal diameter,shorter branches and branchlets.Taking into account that weeds are among the main limiting factors in successful poplar production,their suppression should be considered very seriously(Vasic and Konstantinovic 2008).

Nowadays,there are severalmethods of weed controlin forestry and they can be grouped as mechanical,manual, mulching,chemical,and biological control(George and Brennan 2002;Wagner etal.2006;McCarthy etal.2011). However,producers are increasingly turning to herbicide treatments due to labour shortages,high manpower costs, and large areas.Herbicides can achieve very good efficacy and feasibility in weed suppression(McDonald and Fiddler 1993;Sixto et al.2001;Wagner et al.2004;Fortier and Messier 2006).Mechanical measures are not sufficiently effective for perennial weeds for weeds that develop from rhizomes(Vasic et al.2009).In this way, mechanicaldamage can be avoided and also very often,in the early stages of plant development,mechanical interventions are impossible because of high soil moisture contents.

Herbicide treatment in forestry is mainly based on the experiences in intensive agriculturalproduction(Dixon and Clay 2004),and the agricultural study results are then applied in forestry.The available herbicides controla great number of weed species(Willoughby and Clay 1996),but many herbicides are intended for agricultural crops. Therefore,information on herbicide application in forest nurseries and herbicide selectivity to forest seedlings is insufficient.

A very important factor in the nursery production of poplar seedlings is land,which musthave high potentialof fertility,high water capacity,and loose soil.The production of poplar is based on two different soil types,fluvisol (which can be sandy or loamy form)and humofluvisol (Ivanisevic et al.1997;Roncevic et al.2002).For that reason,the objective ofthis study was to investigate the use of herbicides in poplar nursery production in the two different soil fluvisol-sendy form and humofluvisol.

The study herbicides acetochlor,S-metolachlor,metribuzin,oxifluorfen,and dimethenamid were applied after planting poplar cuttings and prior to poplar and weed emergence.Acetochlor,S-metolachlor,and dimethenamid are herbicides that contain the chemical group chloroacetanilide,which inhibit the synthesis of very-long-chain fatty acids in the plasma membrane(Matthes and Boger 2002).This inhibition offatty acids results in the inhibition of celldivision(Ahrens 1994).Chloroacetanilides are used as pre-emergent herbicides to control the annual grasses and certain annualbroad-leaved weeds(Soltanietal.2007; Bernasinska et al.2013).

Metribuzin is a triazine herbicide which inhibits photosynthesis(Mengistu etal.2000;Flores-Maya etal.2005). Itinterferes with photosynthetic electron transportbetween the primary and the secondary acceptor of PSII(Gronwald 1994).Metribuzin can be applied in pre-emergence weed control of annual grasses and broadleaf weeds(Majumdar and Singh 2007).Oxyfluorfen is a diphenylether herbicide used in the control of broadleaf and grassy weeds.Diphenylethers,such as oxyfluorfen,act on chlorophyll biosynthesis by inhibiting protoporphyrinogen oxidase,an enzyme,which catalyzes the oxidation of protoporphyrinogen to protoporphyrin.Protoporphyrinogen accumulates in the chloroplast and diffuses through the chloroplastic membrane.This extraplastidic accumulation of protoporphyrin is responsible for the toxicity of these herbicides (Duke etal.1991;Jacobs etal.1991;Geoffroy etal.2002).

Materials and methods

Herbicide control in the production of poplar plants was investigated during the period 2009–2010 on the experimental field at the Institute of Lowland Forestry and Environment.Experimental plots were established at two locations,which differed by the physical and chemical characteristics of the soil.Location I(4517036.7100N, 195302.3100E)is on fluvisolsandy form soil,and Location II(4517018.4900N,1953035.3100E)is on humofluvisol soil.The main physico-chemicalcharacteristics ofthe soils are presented in Table 1.

The experiments were established using randomized block design in four replicates,and the size of elementary plot was 24 m2(2.4 m 9 10 m).The experimental plots were planted with Populus 9 euramericana(Dode)Guinier clone‘‘Pannonia’’cuttings,25 cm long and 3 cm wide,with 4–5 buds,prepared 1 month prior to planting, tied in bundles and cold stored.A day before planting,the cuttings were taken from cold storage and soaked in a 1% concentration of copper-oxychloride(25%copper oxychloride).The cuttings were planted manually,with 80 cm distance between rows and 35 cm plant spacing within rows.Each variantconsisted ofthree rows with 30 cuttings in each row,for a total of 90 cuttings.One month after planting,the number of survivors was counted both on the control plot and on treated areas and the survival percentage was calculated to ascertain to which extentthe applied herbicides affected the plant survival.

The main data on the tested herbicides are presented in Table 2.Acetochlor,S-metolachlor,metribuzin,oxifluorfen,and dimethenamid were applied 2 days after planting, using a knapsack sprayer‘‘Solo’’with 300 L of water/ha. The tests included two types of control plots that were not treated with herbicides.Control I was weeded mechanically(one hand-hoeing),and Control II was neither treated with herbicides nor weeded mechanically.

The soilwas wellprepared,because the success of preemergence herbicides requires good soil preparation with the anticipation that herbicide treatments be followed by sufficient rainfall,so that their maximal efficacy can be achieved.Because there was no rainfallduring both study years,the sample plots were irrigated with 5 L of water/m2. Herbicide efficiency(%)was rated 15,30,and 60 days after application of herbicides.The weeds were identified and counted using two 1 m2randomly placed in the treated and untreated halves of each plot.Herbicide effectiveness was calculated by subtracting the value in the treated plot from the value in the untreated plot,by dividing the difference by the value in the untreated plot,and multiplying by 100(Singh et al.2000;Auskalnis and Kadzys 2006; Main et al.2007;Baghestani et al.2008;Hasanuzzaman et al.2009).In that way,efficacy of herbicides shown in percentage,where 0%means no efficacy—control and 100%means total weed control.After the last rating of herbicide efficacy(60 days aftertreatment),allweeds were cut at ground level and the fresh weight of weeds was measured.

Table 1 Main physico-chemical characteristics of the sample plot soils

Table 2 Main data on the study herbicides

During both study years,at the end of the vegetation period,the heightand rootcollar diameter of 30 randomly selected poplar plants were measured both in treatment plots and controlplots.The data on herbicide effectiveness, reduction in weed fresh biomass,and impactof herbicides on poplar height and root-collar diameter were arcsine transformed and analysed by ANOVA.Duncan’s test at P=0.05 level of probability was used to determine the significance of differences between the treatment means.

Results

Herbicide efficacy and selectivity on the study locations

The main data on experiments are presented in Table 3. The differences in the composition of weed vegetation were determined based on two-year research carried out at two locations differing by soil physico-chemical characteristics.On Location I,the most abundant weed species were Ambrosia artemisiifolia L.,Chenopodium album L., Solanum nigrum L.and Echinochloa crus-galli L.The species with high abundance were also Polygonum lapathifolium L.,Amaranthus retroflexus L.,Galinsoga parviflora Cav.and Sorghum halepense(L.)Pers.

During 2009,on Location I,at the first assessment the tested herbicide efficacy ranged between 96.02 and 77.98%(Table 4).The maximal efficacy in weed suppression was achieved by the application of metribuzin (96.02%),and then by applying the herbicide acetochlor (92%).Metribuzin and acetochlorshowed high efficacy on A.artemisiifolia and C.album.Somewhat lower efficacy was attained by herbicides S-metolachlor(90%)and dimethenamid(86%).Although oxyfluorfen showed high efficacy against C.album,S.nigrum L.and A.retroflexus, its average efficiency for all species was the lowest (77.98%).The reason was an abundant presence of A. artemisiifolia and E.crus-galli,which was not strongly affected by herbicide.

During the second and the third assessments,the efficacy of all tested herbicides was somewhat lower in comparison to the first assessment,which is logical given that the herbicide residual effect decreases over time. During the second and the third assessments,the herbicide metribuzin reached the highest efficacy in weed suppression(91 and 86.02%,respectfully),whereas oxyfluorfen efficacy was the lowest(70.98 and 66.98%,respectfully).

On the plots where weeds were controlled using mechanical measures,during the first assessment,the efficacy was very good and accounted for 88%.However, during the second and the third assessments,the values were significantly lower than on the plots treated with herbicides because of the re-emergence of weeds on the plots with mechanical control,which decreased the efficacy.

During 2010,the efficacy of the tested herbicides on Location I during the first assessment ranged between 95.56 and 82.98%;during the second assessment,between 90 and 77.98%;and during the third assessment,between 84.99 and 69.98%.The highest efficacy in the second study year on Location Iwas attained using metribuzin and the lowestby the treatmentwith oxyfluorfen(Table 5).The efficacy of mechanical measures was significantly lower when compared to herbicide treatments in all three assessments.

On Location I during the study years,a number of survivals on the plots treated with metribuzin,showed the symptoms of phytotoxic effects.During the first and the second assessments,the phytotoxicity symptoms were manifested as leaf necrosis,and later on during the thirdassessment,the leaves were completely dry and the plants were dead.The plants with no symptoms of phytotoxic effects developed withoutany visible changes.

Table 3 Main data on experiments

Table 4 Herbicide efficacy on the study locations during 2009

On Location II,the most abundant weed species were Sinapis arvensis L.,S.halepense(L.)Pers.,Sonchus arvensis L.,Datura stramonium L.and C.album L.and the species Chenopodium hybridum L.,Amaranthus blitoides S.Wats.and Setaria viridis(L.)P.B.were also numerous.

During the year 2009,on Location II,during the first assessment the highest efficacy in weed control was achieved by acetochlor(90.02%)and the lowest by oxifluorfen(70.98%).Acetochlor was highly effective on all abundant weeds on Location II,except for the species S. arvensis against which its efficacy was low.Oxyfluorfen efficacy was high on S.arvensis,D.stramonium,and C. album,and lower on the species C.hybridum,A.blitoides, S.halepense and S.viridis.

During the second assessment,the efficacy of the tested herbicides ranged between 82.52 and 75%and during the third assessment,from 79.99 to 64.48%.During all three assessments,the weed suppression efficacy achieved by mechanical measures was significantly lower in comparison to the tested herbicide efficacy,exceptfor oxyfluorfen which attained the lowest efficacy.

In 2010,acetochlor reached the highest efficacy in the suppression of present weed species.The lowest efficacy during the firstand the second assessments was observed in the treatment with oxyfluorfen(82.56 and 77.53%, respectfully)and during the third assessment,in the treatment with dimethenamid(71.99%).The efficacy of this herbicidewaslowerbecauseoftheincreased abundanceof S. arvensis and D.stramonium against which dimethenamid efficacy was low.The efficacy of mechanical suppression was significantly highercompared to the efficacy of S-metolachlor and oxyfluorfen,and during the third assessment, the efficacy was higher compared to dimethenamid,S-metolachlor,and oxyfluorfen.On Location II,the tested herbicides did nothave a phytotoxic effecton poplars.

Table 5 Herbicide efficacy on the study locations during 2010

Effect of herbicides on fresh weight of weeds

The measurements ofweed fresh mass showed a significant reduction under the effect of herbicides compared to the control(Table 6).In 2009,on Location I,the lowestweight of weed fresh mass was measured on the plots treated with metribuzin(108.37 g/m2)and acetochlor(132.50 g/m2).In all treatments,the measured fresh mass was significantly lower than that in the control,which ranged between 153.30 and 190.05 g/m2.In 2010,the greatest decrease in weed fresh mass was attained using metribuzin and dimethenamid(108.85 g/m2),and S-metolachlor(109.52 g/m2). On Location II,during both study years,the most significant reduction in weed fresh mass was achieved using metribuzin and acetochlor.The other treatments also reduced the weed fresh mass compared to the control,and oxyfluorfen was the least effective herbicide.

Herbicide effect on the survival of poplar cuttings

Statistical data processing shows that the study herbicides did not affect survival in rooted cuttings,except for metribuzin,which had a negative effect on Location I (Table 7).During both study years,there was significantly lower cutting survival(56.40%in 2009,and 66.54%in 2010)compared to the other study herbicides.During the third rating,the survival plants did not have the symptoms of phytotoxicity.

On the control plots,which were neither treated mechanically nor with herbicides,the number of survival plants was the lowest on both locations,during the study years.On Location I,in 2009 the percentage of rooted cuttings was 51.15%,and in 2010 62.41%.On LocationII,the rooting percentage in 2009 was 60.15%,and in 2010 59.43%.The abundantpresence ofweeds on control plots made the normal plant development impossible, which was reflected on their rooting.

Table 6 Fresh weight of weeds 60 days after application of herbicides

Effect of herbicides on poplar heights and root collar diameters

The data in Table 8 show that the tested herbicides did not significant effect on the growth of poplar plants.Mean values of poplar heights in variants with herbicides did notdiffer significantly from mean values measured in variants with mechanical weeding.The significantly lower values were recorded on control plots which were neither treated with herbicides nor weeded mechanically.

Table 7 Effect of tested treatments on the rooting of poplar cuttings

Due to high weed competition on controlplots,poplars could not gain their growth potential.During the study years on both locations,mean values of poplar heights in all variants with herbicides were approximately the same; only a significantly higher value,amounting to 3.48 m,was reached on Location II in 2010 in the variant with acetochlor.

The observed diameter values in variants with herbicides did notdiffersignificantly from the values reached in variants with mechanical suppression.During the study years,mean values of poplar root-collar diameters ranged within very narrow limits(Table 9).

This means thatpractically the same diameter increment was achieved in alltreatments,exceptin the controls where the measured values were the lowest.In the conditions of intensive weediness,poplarrooted cuttings could notattain normal development,which in addition to poplar heights, was also reflected on poplar diameters.Statistical data processing did notpointto significantdifferences between the tested treatments with herbicides.

Discussion

The results of the research on the composition of weed flora showed that the differences in the soil physical–chemical characteristics affected the composition of weedvegetation at the study locations.Although the geographic distribution of vegetation mainly depends on climate factors,in each climate zone,vegetation is distributed under the effect of edaphic factors(Andreasen et al.1991;Woo et al.1991;Ugen and Wortmann 2001).

Table 8 Effect of tested treatments on poplar heights

Table 9 Effect of tested treatments on poplar root collar diameters

The tested pre-emergence herbicides significantly decreased weediness compared to the control plots.The highest efficacy in weed suppression was achieved by metribuzin and acetochlor,and somewhat lower by S-metolachlor and dimethenamid.Metribuzin and acetochlor were effective in the suppression of C.album,thespecies that was abundant at both locations.Also,metribuzin and acetochlor were effective in the control of the species S.nigrum and A.artemisiifolia which were abundant on Location I,and the species D.stramonium,S. arvensis on Location II.Although the herbicides S-metolachlor and dimethenamid belong to the same chemical group(chloroacetanilides),their effect on C.album was low(Janjic and Elezovic 2010).

The efficacy of oxyfluorfen was the lowest,but despite of that,its efficacy during the first and the second assessment at both locations was above 70%.Only in 2009, during the third assessmentits efficacy was less than 70%. Oxyfluorfen was effective against C.album,S.nigrum,S. arvensis,and D.stramonium,but its efficacy was low against A.artemisiifolia,E.crus-galli,and S.halepense. Sixto et al.(2001)reported that oxyfluorfen proved its efficacy in controlling weeds in poplar nurseries,and in having a good selectivity.

The analysis of data on height and diameter measurements at the end of the growing season showed that there were no statistically significant differences between the treatment values.Even in the treatments with a lower efficiency index(oxyfluorfen,mechanical weeding),the present weeds did not endanger the poplar development, because weed abundance was significantly lower in comparison to the control.

The study results indicate that all herbicides can be applied in weed control in poplar nurseries,except for metribuzin,which had a phytotoxic effect on sandy soils (Location I).

Being readily soluble in water(Ahrens 1994;Pot et al. 2011)and weakly absorbed on sandy soils(Ludvik and Zuman 2000;Bedmar etal.2004;Shah etal.2009)metribuzin probably into deepersoillayers into the rootzone on Location Iand caused damage and dying ofrooted cuttings.The percentage of rooted cuttings on the plots treated with metribuzin was significantly lower because of phytotoxic effects.Forthatreason,the use ofmetribuzin is notrecommended on the soils lightmechanicalcomposition.

Poplars are highly susceptible to herbicide application (Netzer and Hansen 1992;Buhler etal.1998;Meilan et al. 2002),so several factors should be taken into account.In addition to herbicide chemical composition and structure, quantity,method,and time of herbicide application,climate factors,soil should be considered by all means (Prasse 1985).The content of humus in the soil is especially significant,because humus has a direct effect on herbicide activity because of its adsorption ability.Also, the content of colloid particles reduces herbicide activity because of high herbicide-binding characteristics(Spark and Swift 2002).

During the study years,weediness on the mechanically treated plots was reduced compared to control plots.The applied mechanical measures made it possible for the rooted cuttings to develop normally and reach the determined height and diameter growth.Gourley et al.(1990) also claim that mechanical weed suppression enables the cultivated plants to develop normally and reach the determined heights.Buhleretal.(1998)claim thatweed control strategy should be based on the combination of chemical and mechanical measures.

Mechanicalmeasures alone are notsufficiently effective (Thiffault and Roy 2011)if there are perennial weeds with strong regenerative power,so the measures should be repeated several times(Vasic et al.2009).They are expensive(Willoughby et al.2004)because they require the engagement of a substantialnumber of workers.Also, due to dense weed competition,mechanicalmeasures could lead to unintended damage to poplars,hidden within the dense weed canopy(Thiffaultand Roy 2011).Compared to other available alternative measures,the use of herbicides is a popular and feasible option for many forest users (McDonald and Fiddler 1993;Wagner et al.2004;Willoughby et al.2007;Bolte and Lof 2010).

On the study controlplots,weed competition caused the destruction of a great number of poplars.Because of the abundant presence of weeds,the surviving cuttings could not develop normally and reach the targeted height and diameter growth.Hansen and Netzer(1985)claim that if weeds are not suppressed,as much as 50%of rooted cuttings may be killed and the surviving plants are of poor quality.Anselmi and Giorcelli(1983)reported that the adverse effect of weeds on poplar rooted cuttings is the highest at the time of their formation.If weed growth is abundant during that period,poplar growth is depressed and the plants are killed.For this reason,atthe end of the growing season,the produced plants are of poorer quality and their number is lower than expected.

The study results show that all herbicides reduced the weed abundance and fresh mass atthe study locations.The highest efficacy in weed control was achieved using acetochlor and metribuzin.The tested herbicides did not have a phytotoxic effect on poplar survivals,except for metribuzin,which was phytotoxic to poplars grown on the soil of light mechanical composition.

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received by weed fresh mass measurements showed the reduction in weed mass by all herbicides.The lowest efficacy was shown by oxyfluorfen which resulted in the presence of above-ground masses of weeds on the plots where oxyfluorfen was not effective.Different kinds of soil as well as flora can lead to differences in the effectiveness of herbicides.

Received:7 July 2013/Accepted:10 November 2013/Published online:27 January 2015

Project funding:This paper was realized as a part of the project’’Biosenzing technology and global system for continuous research and integrated management of ecosystems’’(43002)financed by the Ministry of Education and Science of the Republic of Serbia.

The online version is available athttp://www.springerlink.com

Corresponding editor:Chai Ruihai

e-mail:vericav@uns.ac.rs