INTEGRATED WEED CONTROL IN MAIZE

J. Latré2,K. Dewitte1, V. Derycke1, B. De Roo2 & G. Haesaert1

1University Ghent, Faculty of Bioscience Engineering,

Valentin Vaerwyckweg, 1, BE-9000 Gent, Belgium

2University College Ghent,Faculty of Science and Technology,

Valentin Vaerwyckweg, 1, BE-9000 Gent, Belgium

SUMMARY

Integrated pest management has been implemented as a general practice by EU legislation. Asweed control actually is the most important crop protection measure in maize for WesternEurope, the new legislation will have its impact. The question is of course which systems canbe successfully implemented in practice with respect to labour efficiency and economicalparameters.During 3 successive growing seasons (2007,2008,2009) weed control in maize was evaluated, the main focus was put on different techniques of integretad weed control and was compared with chemical weed control.Additionally, during 4 successive growing seasons (2011,2012,2013 and 2014) two objects based on integrated weed control and two objects based on mechanical weed control were compared to about twenty different objects ofconventional chemical weed control. One of the objects based on mechanical weed control consisted of treatment with the flex-tine harrow before and afteremergence in combination with chemical weed control at a reduced rate in 3-4 leave stage. The second one consistedof broadcast mechanical treatments before and after emergence followed by a final in-rowapplication of herbicides and an inter-row cultivation at 6-7(8) leave stage.All trials were conducted on the Experimental farm of Bottelare HoGent-UGent on a sandy loam soil. Maize was growing in 1/3 crop rotation.. The effect on weedgrowthas well as the economical impact of the different applications was evaluated.Combining chemical and mechanical weed control is a possible option in conventional farmingbut the disadvantages must be taken into account. A better planned weed control based on thereal present weed-population in combination with a carefully thought-out choice of herbicidesshould also be considered as an IPM – approach.

INTRODUCTION

Maize (Zea mays L.) is with a cultivated surface of 14 million hectares oneofthemostimportantcropsin the EU Europe (excludingtheex-SovietUnion-republics; FAOSTAT, 2013).Almost 90% of the total maize crop in 11 European regions are treated with herbicidesat least once in a season (Meissle et al., 2010; Pelzer et al., 2012; Vasileiadis et al., 2011, 2013). This dependence on herbicides is relied to the fact that maize is rather sensitive to early competition (Cerrudo et al., 2012) and is often infested by weeds that are highly competitive (Sattin et al., 1992).As the implementation of IPM (Integrated Pest Management) has becomean obligation at the beginning of 2014 (Directive 2009/128/EC; European Parliament, 2009), integrated weed management (IWM) in maize shouldbe a common practice.However, to reach this goal,robust evidence on the sustainability of IWM-strategies is needed to motivate their adoption by stakeholders(Vasileiadis et al.,2015).Over the last fifteen years, environmental and human healthimpact of herbicides use, increase of herbicide resistance, thescarce availability of herbicides for minor crops such as vegetablesand the increase of organic farming were the main factors tostimulate the development of new methods for mechanicalweed control applied solely or combined with herbicides in integrated weedcontrol strategies (Melander et al., 2005; Cloutier et al., 2007).

While purely mechanical and cultural methods are combined to replace labour intensivehand-weeding in organic farming, they can be applied in combination with herbicides(particularly band spraying) to reduce the amount of active ingredient in integrated farmingsystems (Baumann, 1992; Pleasant et al., 1994). Mechanical weed control in maize is and has been practiced in several European countries. For example in the Netherlands between 2000 and 2005,mechanical weed control was a necessary cultivation measure for farmers who wanted to obtain EU-subsidies for corn-cultivation.Preemergence mechanical weed control is done by harrowing with flex-tine harrow.Post emergence mechanical weed controlincludes cultivation between the rows (mainly hoeing andharrowing) and within the rows (finger-, torsion-, brush-, or pneumatic weeders).Further options include flame weeding before or after emergence and ridging later in theseason(van der Schans et al., 2006).

Another possibility is the combination of pre emergence and post emergence harrowing with a flex-tine harrow and finally a reduced dose of herbicide. For broadcast herbicideapplications with reduced doses, the risk of resistance development might be limited byaltering low with full doses in subsequent years. Dosages reduced to typically 50-80% of therate recommended by the manufacturer have already been applied in maize on more than50% of the area in the Netherlands and more than 80 % of the area in Denmark, Germanyand France (Endure, 2007). In tillage systems without soil inversion (no ploughing), which provide improvedsoil quality and reduced erosion, often more herbicides are applied to avoid a build-up ofweed seed banks. Ridge tillage systems combined with mechanical weed control,can be efficient even without herbicide inputs (Cloutier et al., 2007).

Vasileiadis et al. (2015) tested in three EU countries (Southern Germany, Italy and Slovenia) a different IWM-strategy: early postemergence herbicide band application combined with hoeing followed by a second hoeing, herbicide application based on prediction model after scouting of weeds in the fields and tine harrowing at 2–3rd leaf stage of maize and low dose of postemergence herbicide.Results showed that the IWM tools tested in the different countries: (1) provided sufficient weed control without any significant differences in yields, (2) greatly reduced maize reliance on herbicides and (3) IWM implementation was economically sustainable as no significant differences in gross margin were observed in any country compared to the conventional approach.

In Belgium, mechanical weed control in maize is only practiced in organic farming. Although subsidies exist to enhance the application in practice, conventional farmers don’t apply the techniques.In the period of 2001 to 2006 on the Experimental Farm of Ghent University and University College Ghent (Bottelare - Belgium),a long term experiment was conducted in which full mechanical interventions were compared to a combination of mechanical and chemical weed control (Haesaert et al., 2007). The broadcast mechanical interventions with a flex-tine harrow (preandpost emergence) incombination with herbicides gave abetter weed control than use of herbicides alone. Reduced rates of herbicides, even in combination with mechanical interventions gave frequently unfavourable results in case of a high weed density.

The combination of in-row applications of herbicdes (band spraying) with broadcastand between the rows mechanical weed control appeared to give the best weed control and seemed to be the best suitable method to come to a reduced herbicide input.The results of a full mechanical weed control varied from year to year.In order to have more information of the sustainability of IWM- strategies in Belgian circumstancesthe long term experiment was continued, IWC-objects were added to the traditional trials of chemical weed control and a cost calculation was performed.

Materials and methods:

During 3 successive growing seasons (2007,2008,2009) different techniques of Integrated Weed Control(IWC) were compared with Chemical Weed Control(CWC).In the CWC 4 combinations of herbicideswere applied at Normal Rate=Nand at a reduced rate(75% of normal rate). In the IWC-1 treatments 4 combinations of herbicides in 4-5 leavesof maize were applied at Normal Rate=Nand at a reduced rate(75 % NR) in combination with mechanical interventions between sowingand the 3-4 leaves stage. The full mechanical weed control (MWC)consisted of different treatments before and after emergence (flex-tine harrow,cultivator and finger weeder).Finally the IWC-2 treatment consisted of broadcast mechanical treatments between drilling and the 3-4 leave stage in combination with inter-row cultivation and chemical weed control of in-row weeds (band spraying) in 6-8 leaves stage

In the trials 2007-2008-2009 for the chemical treatment,adapted conventional schemes were applied numbered as 1,2,3,4 in table 1.As an example, thechemical treatments of 2007 were the following: 1= flufenacet+terbuthylazin+sulcotrion+foramsulfuron+isoxadifen-ethyl, 2= bentazon + terbuthylazin + dimethenamide-P + mesotrione, 3=S-metholachloor + terbuthylazin + mesotrione + nicosulfuron and 4= pethoxamide + mesotrione + terbuthuylazin + nicosulfuron.Every time the normal rate and 75% of normal ratewas applied.

Additionally, during 4 successive growing seasons (2011,2012,2013 and 2014)two IWC objects were compared to twenty different objects of traditional full chemical weed control –objects T).The CWC treatments consisted of: pre emergence treatments (sometimes in combination with post emergence) and post emergence (in general 3-4 leaves stage) with and without terbuthylazin.Additionally an IWC-1 treatment was applied which consisted of a combination of mechanical weed control (flex-tine harrow) andchemical weed control (6-leaves stage, ¾ of normal rate). Finally an IWC-2 treatment was applied ofbroadcast mechanical treatments between drilling and 5-6leave stage:flex-tine harrowand a final inter-row cultivation in combination with a herbicide in-row application ( band spraying; 6 leaves, normal rate).Following mechanical weed control measures were carried out:different applications of the flex-tine harrowwere appliedpre emergence, cancelled in the period of emergence until 2-3 leaves, performed again one to two times and stopped at the 4 leave stage. Theinter-row cultivator with spring-loaded steel rods was used between 5-6 leave stage and 7-8 leaves stage.The finger weeder for in row application in the full mechanical treatment was used between 5-6 and 7-8 leaves stage.Due to very wet circumstances in the first month after drilling in 2014, it was impossible to apply the IWC-1 and IWC-2 treatment.Therefore the further results are not discussed.

Experiments were set up on sandy loam soils at the Experimental farm Bottelare in a normal crop rotation. Normal crop husbandry measures were taken with drilling between 20thApriland 10thMay at a plant density ranging from 95.000 seeds to115.000 seeds/ha.The fertilization wasbased on soil analysis and consistedmainly of 150 kg/ha N, 75 to 90 kg/ha P2O5 and 200 – 250 kg/ha K2O.The broadcast applications of herbicides were applied with a AZO knapsack sprayer. The sprayboom of 3 m was equipped with fan nozzles (type TJXR 8001); the spraying volume was for all treatments 300 l/ha. The in-row applications of herbicides were made witha cultivator equipped with a two fan nozzle configurations per row; the spraying volume was for all treatments 300 l/ha.

The trials were set up as a completely randomized block design with 3 replications.The plots for mechanical weed control were arranged in long strips of at least 50 m length and 6 m width. The plots for chemical control were 12 m length and3m width.

The weeds werecounted in 16 quadrats of 25 cm x 25 cm per plot of 36 m².The yield was determined according to the SEMZABEL protocol (Haesaert, 2007); growth inhibition was measured using the EWRC-scale (ref),total DM yield was calculated in% of untreated control (were cleaned by hand weeding begin July).In 2013, yield could not be determined.The costs of treatments (without TAV) were calculated based on: the actual (former) chemical weed control of in-row weeds (6 leaves, normal rate) broadcast spraying by contractor: 23 euro/ha (company:Suenaert).As broadcast mechanical weed control is not common in Belgium in corn there are no available prices from the contractor perspective.So this cost was calculated based on data from KWIN-AGV (2012) and CCBT (Delanote, 2015):broadcast cultivation with flex-tine harrow 40 euro/ha,inter-row cultivation with cultivator and in-row chemical weed control 60 euro/ha.

Statistical analysis

SPSS 20.0 (SPSS Inc., Chicago, IL, USA) for Windows was used to carry out the statistical computations for testing for normal distribution of the plant density and the yield with the one sample Kolmogorov-Smirnov Test. Homoscedasticity was tested with the Levene’s test. If the assumptions of normality and homoscedasticity were fulfilled the data were processed with a one way Anova to detect if there were significant differences between groups of data.

RESULTS

Trials 2007-2009:With focus on integrated weed control

The results of the weed controland the yield (both in% versus the control=100 %);the growth inhibition andplant density (plants/ha) are given in table 1. The results of the trials 2007-2009 confirm the former good results of the combination of general broadcast mechanical interventions with broadcast applications of herbicides (reduced rate) (=IWC1) (Haesaert et al.,2007). The reduced rates of herbicide even in combination with mechanical interventions gave in the three years good results.This was also the case for the combination of mechanical weed control withfinalin-row applications of herbicides (=IWC2).The number of remaining weeds was acceptable. The full mechanical weed control (=MWC) was less successful.In fact, a considerable amount of weeds were not destroyed, especially in the row, and a serious thinning out and growth inhibition of the crop could be noted, resulting inlower yields.

Trials 2011-2013:With focuson n chemical weed control

The results of the weed control, the yield (both in% versus the control=100%) andplant density (plants/ha) are given in table 2,3 and 4 for respectively the years 2011, 2012 and 2013.The weed population, the weed density and the circumstances varied from year to year.In 2011 and 2012, plant density was significantly lower in case of integrated weed control. The several passages with the flex-tine harrow caused a considerable thinning out.As a consequence, yield was significantly lower.Exceptionally, in case of IWC-1 in 2012, yield was comparable to the CWC-objects.It’s difficult to generalize over the yearsfor the results of the chemical weed control as the results are given as means of a variable number of different combinations (pre and post emergence, combination of pre and post and with or without terbuthylazin).Pre emergence was quite successful in 2012 and 2013 due to wet conditions.Beyond expectation, CWC pre emergence + post emergence gave a less good result in 2012,probably due to specific trial circumstances.The CWC-objects without terbuthylazin are in general as successful as with terbuthylazin.Nevertheless, in 2013, the results onMatricariachamomilla,Stellariamedia and Chenopodiumalbum were less for terbuthyl ?.The other observed small differences in 2011 and 2012 must be interpreted very carefully because the number of the involved weeds is often quite low.IWC-1 gave a very good weed control in 2011 and 2012.In the year 2013 with a high weed density, results were inferior.IWC-2 gave some remaining weeds, especially between the rows in 2011 and 2012.In 2013 the weed control of IWC-2 was quite unsuccessful.

The involved cost of the different treatments is comparable over the years, of course depending on the number of passages in case of IWC-1 and 2.The cost of a single chemical weed control in 3-4 leave stage with or without terbuthylazin is comparable.This single treatment can be considered as common practice.IWC 1 and IWC-2 arerespectively about 110 euro/haand 120 euro/ha more expensive.In case of CWC pre E. + post E. which often occurs in a situation of monoculture with higher weed density of difficult to control weeds, than the extra cost is respectivelyabout 60 and 70 euro.

DISCUSSION and CONCLUSIONS

Based on the results of 2007-2009and former results (Haesaert et al., 2007) one can conclude that full mechanical weed control (MWC) is not sufficient and not applicable in terms of a realistic IWC in conventional farming.IWC-1 and 2 are applicable in conventional farming. The broadcast mechanical interventions with a flex-tine harrow (PreE – PostE) incombination witha reduced dose of herbicide (IWC-1) gave in general a good weed control, in line with Pannacci and Tei (2014) and Vasileiadis et al. (2015). In case of a high initial weed density, results can be inferior.This is in line with the results of Haesaert et al. (2007).The results of IWC-2in terms of weed control were quite good in the trials in the period 2007-2009 but less successful in the period 2011-2013.

1

Table 1.Results of the weed controland the yield (both in% versus the control=100 %); growth inhibition andplant density (plants/ha) (Trials Experimental Farm Bottelare 2007-2009)

Treat-ment / STEME1 / CHEAL1 / POLPE1 / POAAN1 / MATCH1,2 / LOLPE1,2 / Inhib.4 / Plants/
ha / Yield5
3/43 / N3 / 3/4 / N / 3/4 / N / 3/4 / N / 3/4 / N / 3/4 / N / 3/4 / N / 3/4 / N
IWC-1 / 99000/
85333/
77733
1 / 0 / 2/0/06 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 1 / 1 / 95.2/89.7/106.66 / 94/92.3/97.4
2 / 0 / 0 / 4/0/0 / 9/0/0 / 0 / 0 / 0 / 0 / 0 / 0 / 29 / 0 / 1 / 1 / 92.6/93/- / 99/94.0/-
3 / 0 / 0 / 0/5/0 / 0 / 0 / 0/4/0 / 0 / 0/1/0 / 0 / 0 / 0 / 0 / 1 / 1 / 92.6/96.6/104.8 / 94.5/96.8/-
4 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 7 / 1 / 1 / 95.1/93.7/105.3 / 92.3/95.1/106.8
CWC / 109889/
102278/
90619
1 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 1 / 1 / 99.9/99.5/111.1 / 98.6/97.2/108.7
2 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 6 / 0 / 29 / 7 / 1 / 1 / 102/102/105.7 / 100.5/99/99.8
3 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 36 / 29 / 1 / 1 / 101/104.2/104.8 / 101.3/106.8/100.2
4 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 0 / 29 / 50 / 1 / 1 / 96.6/102.1/- / 98.8/101.3/108.6
MWC / 13/38/4 / 15/12/9 / 7/9/6 / 8/7/2 / 4 / 24 / 3/4/4 / 87556/
89778/
79667 / 94.7/
90/
91.7
IWC-2 / 4/3/2 / 2/2/3 / 7/0.3/0 / 0/2/0 / 3 / 7 / 2/2/2 / 98667/
89778/
79667 / 95.1/
98.6/
103.9
Contr.
(Plants/m²) / 51/7/28 / 23/14/27 / 10/37/24 / 4/28/20 / 11 / 5 / 1/1/1 / 105333/
104444/
85311 / 100=23 ton/ha
100=22.6 ton/ha
100= 14.9 ton/ha
Fcal.-sign. / */*/** / NS (C.V.=8.2 %, 8.2 %, 9.8 %)

1STEME:Stelaria media, CHEAL=Chenopodium album, POAAN=Poa annua, POLPE=Polygonum persicaria en LOLPE=Lolium Perenne

2MATCH: only in 2009 and LOLPE only in 2008

3N = normal rate and ¾ = 75 % of the normal rate

4Inhibition according to ERWC scale

5Yield: relative in% to the control(Contr.)

6data of 2007,2008 and 2009 are given, separated by slash-sign

1

Table 2. Results of the weed control,the yield (t/ha)andplant density (plants/ha)(in% versus the control=100%) (Experimental Farm Bottelare, 2011)

treatment / ECHCG1 / CHEAL1 / POAAN1 / POLCO1 / plants/ha / yield/ha / cost (euro/ha)
control (weeds/m²) / 3 / 11,5 / 4 / 2,5 / 99.250 / 20,9t/ha
control ( %) / 100 / 100 / 100 / 100 / 100 / 100
CWC Pre.E.2( %) / 58,3 / 32,6 / 0,0 / 140,0 / 99,5 / 96,0 / 136
CWC Pre.E+Post E.3 (1) ( %) / 0,0 / 0,0 / 0,0 / 10,0 / 97,5 / 95,7 / 192
CWC Post E. - T (5)6( %) / 0,0 / 0,0 / 0,0 / 26,0 / 99,7 / 97,2 / 105-129
CWC Post E. + T (8)6( %) / 9,4 / 0,5 / 0,8 / 3,8 / 99,0 / 99,8 / 132-156
IWC-1 ( %) 4 / 0,0 / 0,0 / 0,0 / 0,0 / 80,4 / 78,4 / 272,0
IWC-2 ( %) 5 / 13,9 / 11,6 / 8,3 / 33,3 / 74,8 / 81,3 / 259,8
Fcal.-significance / *** / ***
1 ECHCG= Echinochloa crus-galli,CHEAL = Chenopodium album, POAAN = Poa annua, POLCO = Fallopia convolvulus
2 and 3CWC=chemical weed control, Pre Emergence/Post emergence, number of objects between ()
4 Integrated Weed Control: 4 harrow applications + chemical weed control 3/4 normal rate (7-8 leaves)
5 Integrated Weed Control: 4 harrow applications + cultivator between row + in row chemical weed control normal rate(7-8 leaves)
6CWC Post E. with (=+T) or without (=-T) terbuthylazin, number of objects between ()

Table 3.Results of the weed control,the yield (t/ha)andplant density (plants/ha)(in% versus the control=100%) (Experimental Farm Bottelare, 2012)

Treatment / CHEAL1 / ECHCG1 / MATCH1 / SENVU1 / STEME1 / POLAM1 / plants/ha / yield/
ha / cost (euro/ha)
control (weeds/m²) / 51,8 / 5,5 / 5,5 / 21,5 / 5,8 / 2,5 / 103500 / 21,7 t/ha
control ( %) / 100 / 100 / 100 / 100 / 100 / 100 / 100 / 100
CWC Pre.E.2( %) / 7,7 / 9,1 / 0,0 / 0,0 / 0,0 / 240 / 103,9 / 113,9 / 136
CWC Pre.E+Post E.3 (1)( %) / 10,2 / 14,0 / 18,6 / 9,3 / 9,7 / 64,2 / 103,1 / 112,6 / 176
CWC Post E. - T (7)6( %) / 0,1 / 6,5 / 13,0 / 0,5 / 1,2 / 44,3 / 103,8 / 113,2 / 113-143
CWC Post E. + T (5)6 ( %) / 1,2 / 9,1 / 11,2 / 0,0 / 0,0 / 47,3 / 102,4 / 113,0 / 126-145
IWC-1 ( %) 4 / 0,0 / 0,0 / 0,0 / 0,0 / 0,0 / 10,0 / 84,5 / 108,7 / 232,0
IWC-2 ( %) 5 / 4,5 / 48,5 / 0,0 / 1,2 / 2,9 / 96,7 / 68,6 / 100,3 / 220,0
Fcal.-significance / *** / ***
1 ECHCG= Echinochloa crus-galli,CHEAL = Chenopodium album, MATCH= Matricaria chamomilla, SENVU=Senecio vulgaris, STEME = Stellaria media,POLAM = Persicaria amphibia
2 and 3CWC=chemical weed control, Pre Emergence/Post Emergence, number of objects between ()
4 Integrated Weed Contol: 3 harrow applications + chemical weed control 3/4 normal rate (7-8 leaves)
5 Integrated Weed control: 3 harrow applications + cultivator + in row chemical weed control normal rate(7-8 leaves)
6CWC Post E. with (=+T) or without (=-T) terbuthylazin, number of objects between ()

Table 4.Results of the weed control,the yield (t/ha)andplant density (plants/ha)(in% versus the control=100%) (Experimental Farm Bottelare, 2013)