Efficiency of Some Post Emergence Acetyl Coenzyme A Carboxylase-Inhibitor Herbicides Against Certain Grassy Weeds in Canola Fields

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INTRODUCTION
Canola (Brassica napusL.) is one of the most economically important oilseed crops worldwide which grown mainly for edible vegetable oil and biodiesels production as well as animal feed.Canola seeds is a rich source of oil (about 40 -45%) and protein (25%) and it is cultivated in more than 120 countries mostly in Asia, Europe, North America and Australia (Roshdy et al. 2008).The oil seed crops production area is still limited that make up 1.8% of the total agricultural land in Egypt.Thus, there is a national target to increase land cultivated with oil seed crops include canola to fill the huge local oil production gap (more than 85%) (Kandil and Gad 2012).Canola plants during its initial growth stages are very sensitive to weeds interference (Kaur et al. 2015).Weeds are one of the most problematic pests of canola all over the worldwhich caused considerable loss in quantity and quality of canola yield production (Mekki et al. 2010;Khan et al. 2003).There are many various grass and broadleaf weed species infested canola fields in the world and resulting in yield loss of 20-50% (Kaur et al. 2015).Among different grassy weeds, Phalaris minor Retz.And Avenafatua L. are the two most widespread, noxious and competitive annual grassy weeds present in canola and other winter crops in the world (Bagherani and Shimi 2001;Karimi et al. 2016;Khan et al. 2008).Dew and Keys (1976) stated that the yield loss of canola by wild oat competition was 32%.
Herbicides are the most effective, cheaper and widespread strategic method to control weeds in canola and other crops as compared to conventional weeds control methods such as hoeing and tilling (Delchev and Georgiev 2015).Many postemergence herbicides such as fluazifop-p-butyl, quizalofop-p-ethyl, fenoxaprop-pethyl and clodinafop-propargyl (Aryloxyphenoxypropionate "AOPP" group), and clethodim, tralkoxydim and sethoxydim (cyclohexanedione "CHD" group) as well as pinoxaden (phenylpyrazoline "DEN" group) are the common and popular graminicides recommended for control several grass weeds such as Phalarisspp and Avenaspp in major dicotyledonous crops include canola in the world (Valaie et al. 2012;Rashed-Mohassel et al., 2010).All these graminicides inhibit acetyl coenzyme A carboxylase (ACCase),thereby blocking fatty acid synthesis in the grass weeds thus they called as ACCase-inhibitors(Kobek et al. 1988).However, although these are graminicides, however some of these herbicides such as clethodim have been exhibited adverse effect on growth and yield of canola plants (Zerner and Wheeler 2013).Also, cycloxydim, quizalofop-p-ethyl and propaquizafop provided good control of P. minorRetz.,BromustectorumL. and Setariaviridis L. Beauv.with no injury effect on canola yield whereas sethoxydim and fluazifop-p-butyl were also effective on grass weeds but they caused adverse effect on canola plants (Valaie et al. 2012).Little information is known about control of grass weeds in canola in Assiut.Thus, the main investigation of this research was to evaluate the effect of certain ACCase-inhibitor and an ALS-inhibitor herbicides against the two noxious grass weeds, P. minor Retz and A. fatua L., in canola fields at Assiut, Egypt.

MATERIALS AND METHODS
The present study was conducted at the Plant Protection Department Farm, Faculty of Agriculture, Assiut University, Assiut, Egypt during 2014-2015 and 2015-2016 winter season.The soil was clayey.Canola variety Serw 4 was sown on the first and 23 th. of November in 2014 and 2015, respectively.The experimental plot size was10.5 m 2 , 3 m × 3.5 m, consisted of 6 ridges of canola with 3 m long and 58 cm apart between-ridges.Full package of agricultural practices like irrigation, fertilization and insect control for canola were followed uniformly and all broadleaved weeds were removed by hand.The grass weed control treatments included five post emergence ACCase-inhibitors and an ALS-inhibitor herbicides, hand hoeing and weedy check.
The experimental treatments were established as randomized complete block design with three replications in both winter seasons.The selected herbicides were sprayed on broadcast applications by knapsack sprayer at water spray volume of 200 L fed -1 .Data Recorded: Each grass weed P. minor and A. fatua was hand-pulled and collected separately from one square meter area in each plot and then its fresh weight were recorded 30 days after treatments (DAT) in both seasons.At harvest, all canolaplants from the middle two rows of each canola plot were harvested in 2014/2015 season but in 2015/2016, all canola plants from each plot were harvested early in the morning to avoid seeds shattering and placed on big plastic sheet to dry on air and under sunshine.Canola seeds of each plot were separated from the siliques manually and cleaned then the seed yield (kg fed -1 ) was recorded.

Statistical Analysis:
Density and fresh weight of P. minor and A. fatua and its rates found in weedy check plots were calculated.The efficiency of grass weed control treatments were also estimated and the data of each experiment was expressed as percent fresh weight reduction of grass weeds as compared with weed control.After that, data were transferred using square root of x + 0.5 to normalize the distribution then each one subjected to analysis of variance separately and means of treatments were compared by LSD test at 5% level of probability (Steel and Torrie 1980).

A-Effect of weed control treatments on grassy weeds
Table (1) showed that canola fields were infested mainly with the two serious grassy weeds Phalaris minor Retz and Avenafatua L. during 2014/2015 and 2015/2016 seasons.P. minor was dominant than A. fatua where it had the highest weed density 37.3 and 257.0individual m -2 with weed density rates of 84.9% and 94.8% and its fresh weight of 522.5 and 5070.0gm -2 with rates of 68.7% and 83.0% in 2014/2015 and 2015/2016, respectively.The weed density of A. fatua were 6.7and 14.0individual m -2 and its fresh weight were 237.7 and 1040.5gm -2 , respectively in both seasons with weed density rates of 15.2 and 5.2% and their fresh weight rates of 31.3 and 17.0%, respectively.Both P. minor and A. fatuawere recorded as major serious grassy weeds in canola fields all over the world (Khan et al. 2008;Valaie et al. 2012;Karimi et al. 2016).
In 2014/2015, results in Table 2 indicated that all selected ACCase-inhibitors (fenoxaprop-p-ethyl, quizalofop-p-ethyl, clethodim and clodinafop + pinoxaden) and an ALS-inhibitor (flucarbazone-sodium) as well as hand hoeing treatments were effective against P. minor and A. fatuaand achieved a significant high fresh weight reduction in both grass weeds compared to weedy check after 30 DAT.The reduction in fresh weight were ranged from 92.9 to 98.9% for P. minor and 95.5 to 99.7% for A. fatua as well as 93.8 to 99.1for total grass weeds versus weedy check.
In 2015/2016, results in Table 3 revealed that all tested ACCase-inhibitors included trakoxydim, clodinafop + pinoxaden, quizalofop-p-ethyl, clethodim and hand hoeing treatments also exhibited high efficacy against the target grassy weeds and significantly reduced fresh weight of P. minor by 88.0 to 98.4% and A. fatua by 91.8 to 99.8% as well as total grass weeds by 89.3 to 98.7%, 30 DAT compared to weedy check.
In general, all selected ACCase-inhibitors, an ALS-inhibitor herbicide and hand hoeing treatments showed effectiveness against both P. minor and A. fatuaweeds and they significantly decreased the fresh weight of the individual and total grass weeds versus weedy check in both seasons (Tables 2 and 3).Various ACCaseinhibiting herbicides include clodinafop, quizalofop-ethyl, fenoxaprop, fluazifop, propaquizafop and tralkoxydim possessed excellent efficacy against graminaceous weeds include P. minor and A. fatuawith selectivity in canola and increased in the crop seed yield (Tibets and Saskevich 2006;Saskevich et al. 2009;Khan et al. 2003Khan et al. , 2008;;Delchev and Georgiev 2015).Chaudhry et al. (2011) demonstrated that clodinafop provided good control of grass weeds (98.37%) in canola and increased the crop yield by 33.23%.Valaie et al. (2012) detected that cycloxydim, fluazifop, propaquizafop, quizalofop and sethoxydim achieved excellent efficacy on A. fatuaand other grass weeds infested canola and propaquizafop and quizalofop-ethyl were performed as the most potential ones.Alvi et al. (2004) confirmed that clodinafop and fenoxaprop provided good (more than 95%) control A. fatuaand P. minor and increased grain yield of wheat.

B-Effect of Weed Control Treatments on Canolacrop:
Flucarbazone-sodium killed all canola plants after 30 days from its application thus this ALS-inhibiting herbicide should not be used to control grass weeds in canola and carefully when it applied next to canola fields.Indeed, the persistence of residues of some ALS-inhibitors such as chloursulfuron, traisulfuron and mesosulfuron plus iodosulfuron from the previous crop possessed phototoxic and inhibitory effects on canola and reduced crop yield i.e., 13 and 20% (Fletcher et al. 1996;Kim et al. 1997;Delchev and Georgiev 2015).
Clethodim exhibited also phytotoxic injury symptoms on some canola plants at the flowering and siliques development stages which were observed as deformation and destroyed in the flowers and siliques on the main stems but not or very few on the secondary branches of affected plants (Fig. 1).A slight injury symptomon the flowers and siliques was also observed on some canola plants treated with clodinafop + pinoxaden.Furthermore, the effect of clethodim on these canola plants were more than that treated with clodinafop + pinoxaden.However, the affected canola plants particularly treated with clodinafop + pinoxaden then clethodim performed ability to decrease this inhibitory action on the flowers and siliques of the main stems in the initial growth of crop through complete growth, flowering and consequently siliques development of the secondary branches in these plants.
Phytotoxicity effects on canola have been confirmed as a delay in flowering and disruption in the flowers and siliques shape after the canola plants treated with some different herbicides such as metribuzin (Sharma and Mishra 1997;Khan et al. 2008;Chaudhry et al. 2011).Also, clethodim caused various injury symptoms on plants of different canola varieties which include a few change in the color of canola leaves and main damage in the flowers and siliques resulting in decreasing in the crop yield (Zerner and Wheeler 2013).They also detected the variability in response of canola varieties to different rates and application times of clethodim and results indicated that canola variety Garnet exhibited tolerance to clethodim at 0.5 L/ha without any yield loss but other varieties like TT Gem and Hyola were affected by this herbicide with yield losses about 13% in both.
However, other tested ACCase-inhibitors (quizalofop-p-ethyl, fenoxaprop and tralkoxydim) did not cause any phytotoxic injury or adverse effects on canola plants in any stages after its application.Similar results were confirmed by Khan et al. (2008) and Valaie et al. (2012) who used the same ACCase-inhibitors to control grass weeds in canola.components from flowers, pods, seeds per pods that consequently due to increase the canola seed yield (Mekki et al. 2010;Chaudhry et al. 2011;Roshdy et al. 2008).Hand hoeing twice also resulted in a decrease in the populations and biomass of various weeds and increased in the yield and yield components of canola and Indian mustard (Mekki et al. 2010;Rajput et al. 1993;Singh et al. 2001).In contrast, interference of P. minor and A. fatuawith their canola plants on the main soil nutrition, moisture, sun light and space led to inhibit the growth and flowering and siliques development of canola then consequently reduced the crop yield to the lowest quantity in weedy check plots during both seasons.Also, canola is a slowly growing oil crop thus it exposed to severe interference by many annual weeds include P. minor and A. fatuathat cause reduction in the growth and development of crop plants as well as a large yield loss (Blackshaw and Harker 1992;Harker 2001;Pacanoski 2014;Roshdy et al. 2008).Karimi et al. (2016) stated that increases of A. fatua populations led to reduced number of siliques, seeds in each siliques and seeds weight and subsequently decrement the canola yield.Yield losses caused by weeds in canola were ranged from 23 to 64% (Bagherani and Shimi 2001), 48% (Pacanoski 2014) and 50.40% (Miri and Rahimi 2009) as well as in Indian mustard from 30 to 50% (Gill et al. 1984).Tomass (1992) confirmed that competition of annual and perennial weeds with oilseed rape has decreased it yield through inhibition the crop growth and reduced the fertile of flowers and siliques.
In conclusion, all selected ACCase-inhibitors (particularly tralkoxydim) and hand hoeing treatments were high effectively against the two common and serious grassy weeds, A. fatuaand P. minor, in canola fields in Assiut in both seasons and caused in improvement in the canola seed yield compared to weedy check.Flucarbazone-sodium should not be sprayed for controlling grassy weeds in canola.More studies are needed to determine the response of other canola varieties to the selected and other ACCase-inhibitor herbicides used in Egypt.

Table 1 :
Density and fresh weight of grass weeds found in weedy check plots in canola fields during 2014/2015 and 2015/2016.Table2: Effect of selected post-emergence graminicidesand hand hoeing treatmentson fresh weight of P.minor and A. fatuain canola fields during 2014/2015season.

Table 3 :
Effect of selected post-emergence graminicidesand hand hoeing treatmentson fresh weight of P.minor and A. fatuain canola fields during2015/2016season.
* Means followed by the common letter(s) within a column are not significantly different at 5% level of probability.