Article Use of Living, Mowed, and -Incorporated Cover for Control in Apricot

Nihat Tursun 1, Do˘ganI¸sık 2, Zeynep Demir 3 and Khawar Jabran 4,* ID

1 Department of Protection, Faculty of , Turgut Ozal University, Malatya 44210, Turkey; [email protected] 2 Department of Plant Protection, Faculty of Agriculture, Erciyes University, Kayseri 38039, Turkey; [email protected] 3 Soil, and Water Resources Central Research Institute, Ankara 06172, Turkey; [email protected] 4 Department of Plant Protection, Faculty of Agriculture and Natural Sciences, Duzce University, Duzce 81620, Turkey * Correspondence: [email protected]; Tel.: +90-380-5412294 (ext. 2638)

 Received: 30 June 2018; Accepted: 13 August 2018; Published: 16 August 2018 

Abstract: Apricot fruits provide important health, economic, and nutritional benefits. damage apricot production directly and host the pests that cause damages to apricot trees. However, very few studies are available on in apricot orchards. This research work was aimed at evaluating five cover crops for weed suppression in apricot . The effect of living, mowed, and soil-incorporated cover corps on weeds was recorded and compared with application and . The cover crops were Vicia villosa Roth., Vicia pannonica Crantz, Triticale + V. pannonica, Phacelia tanacetifolia Benth., and Fagopyrum esculentum Moench. Five major weed species in the experimental area were Amaranthus retroflexus L., Convolvulus arvensis L., Tribulus terrestris L., Sisymbrium officinale (L.) Scop., and Sorghum halepense (L.) Per. The highest biomass production was noted for Triticale + V. pannonica in 2015 and for P. tanacetifolia in 2016. Living cover crops were effective in decreasing the weed biomass compared with the control. Both mowing and soil incorporation of cover crops were effective in decreasing weed richness and density over control. Mowed or soil-incorporated cover crops were more effective than or mechanical weed control, while F. esculentum was the least effective cover for suppressing weeds in apricot orchard. The results of our studies implied that cover crops could be used for weed control in apricot, and their mowing or soil incorporation could enhance their efficacy.

Keywords: weeds; apricot; cover crops; non-chemical weed control; mowing; soil incorporation

1. Introduction Apricot (Prunus armeniaca L.) is a member of family Rosaceae and genus Prunus and probably originated in the Central Asia, Turkey, or Western China. Fruit from apricot possesses high nutritional and health benefits and provides significant economic gains. Currently, the global production of apricots is 3.88 million tons, which is harvested from an area of 0.58 million ha [1]. Out of this apricot fruit production, 55.5% is contributed by Asia, nearly 26% and 14% is contributed by Europe and Africa, respectively while rest comes from other parts of the world. Turkey makes itself the largest producer of apricot with an average annual production of more than half million tons followed by Iran, Uzbekistan, Italy and Pakistan [1]. Climatic conditions in some areas of Turkey (particularly those in Malatya region) are highly supportive for apricot production, and the country is rich in genetic resources for the (apricot) fruit plants.

Agronomy 2018, 8, 150; doi:10.3390/agronomy8080150 www.mdpi.com/journal/agronomy Agronomy 2018, 8, 150 2 of 10

Apricot production is constrained by several factors including those of diseases, weeds, insect pests, soil erosion, and other biotic and abiotic factors. Weeds infest the apricot orchards and decrease its productivity and quality [2,3]. A study indicated that more than 50 weed species infested the apricot orchard, and important among these were Euclidium syriacum (L.) R. Br., Veronica polita Fr., and Polygonum aviculare L. [4]. Along with other damages, the weeds may also host the pathogens that cause diseases in apricot or other fruit plants. For instance, some of apricot weeds could act as a host for plum pox virus [5,6]. may play a significant role for weed management in apricot plants. Glyphosate application and mechanical weed control are important among the current weed control practices in apricot farming. These two practices are expected to provide weed-free apricot fields. However, coverless (bare) apricot fields may result in increased erosion and run-off, decreased soil organic matter and moisture contents, and damage the soil physical and chemical properties [7]. Additionally, a few other problems are also associated with the use (particularly if over-applied) of herbicides for weed control in apricot fields. Evolution of herbicide resistance in weeds and environmental pollution are the most important among these [8–10]. The situation requires that there be weed control techniques that can provide weed suppression and soil cover as well. The use of cover crops may be the most suitable choice to achieve the objectives of soil conservation and weed management simultaneously. Previously, cover crops have been used for suppressing weeds in field crops and fruit orchards [11–14]. For example, cereal rye (Secale cereale L.) applied as cover crop could suppress the herbicide-resistant Amaranthus palmeri (S.) Wats. [15]. The use of cover crops has also been reported for suppressing weeds in perennial fruit orchards and other horticultural crops [16–19]. For example, cover crops of crimson clover (Trifolium incarnatum L.) and barley (Hordeum vulgare L.) reduced the weed infestation in vegetables such as crookneck squash (Cucurbita pepo L.) and broccoli (Brassica oleracea L.) by 50% compared to the un-weeded control [20]. Cover crops including V. villosa and Festuca arundinacea Schreb. were effective in suppressing the weeds and increasing of hazelnut orchards [21]. In addition to weed control, the cover crops could also improve soil chemical and physical properties [22]. Previously, very few studies have addressed weed infestations and their management in apricot cultivation. To the best of our knowledge, no studies were available that may explain the use of cover crops for weed control in apricot cultivation. Hence, the current research work was planned to assess the efficacy of several cover crops for weed control in apricot cultivation. We aimed to determine the weed suppression capacity of cover crops in living, mowed or soil incorporated forms. The study was also aimed at comparing the cover crops with mechanical control and nonselective herbicide (glyphosate) for a sustainable weed control in apricot orchards.

2. Materials and Methods

2.1. Experimental Site Field studies were conducted during 2014 to 2016 in the experimental apricot orchard at Inönü˙ University, Agricultural Faculty, Turkey on a clay soil (20% sand, 28% silt, 52% clay, 1.7% organic matter, and pH 7.4). The experimental site was located at 38.47 N–38.34 E and had an average temperature of 13.4 ◦C in 2015–2016 growing season and mean annual precipitation of 420 mm. The apricot orchard was 10 years old. Plant spacing was 8 m within the row and 8 m between the rows.

2.2. Field Trial Annual cover crops were used for weed control in the experimental area in the apricot orchards. Vicia villosa (hairy vetch), V. pannonica (Hungarian vetch), a mixture of V. pannonica Crantz and Triticale (V. pannonica 70% + Triticale 30%), and Phacelia tanacetifolia (lacy phacelia) were used as winter cover crops, and Fagopyrum esculentum (buckwheat) was used as summer cover crop. Fagopyrum esculentum, which is a concealment plant for the summer, was planted on 21 April 2014 and 5 May 2015, and the Agronomy 2018, 8, 150 3 of 10 other winter covering plants were planted in the fall periods of the years on 23 October 2014 and 23 October 2015. Before planting of the cover crops, weeds present in the field were removed either manually or mechanically. In each of the study years, the first soil cultivation was done during the first week of November, and soil preparation was done in mid-April before sowing of the cover crops (for the summer cover crops). For the winter cover crops, the first soil cultivation was done in mid-September, and soil preparation was done during the first week of November. There was a 50 cm distance between the cover crops and the apricot plants. The results of the experiments were recorded in 2015 and 2016 for summer and winter cover plants. The experiments were established in a randomized block design with four replications. Experiment also included control plots, herbicide applications and mechanical weed control. Each plot was 80 m2 (4 × 20 m). Consecutive plots were separated with a buffer zone with no cover crop. The cover crop were broadcast and incorporated into the soil. Seeding rates were 150 kg ha−1 for hairy vetch and Hungarian vetch, 30 kg ha−1 for lacy phacelia and 50 kg ha−1 buckwheat. The cover crop treatments were maintained in the same (respective) plots throughout the duration of the experiment. Cover crops were at flowering stage on 15 May 2015 in the first year of study and on 24 May 2016 in the second year of study. After the flowering period of the cover crops, half of the parcels with cover crops in experiment were incorporated into the soil using two passes of a double disk to a depth of approximately 10 cm (i.e., soil incorporation treatment), and the other half was mowed without any treatment and left as on the soil (i.e., mowing treatment). Cover crops were mowed or incorporated into the soil on 20 May during 2015 and 3 June during 2016. Mechanical weed control comprised use of rotary hoeing and herbicide treatments included the application of glyphosate at 2.40 kg a.i. ha−1 after the weeds emerged and were growing actively. Herbicide application and mechanical weed control were practiced when the weeds were at 4–8 leaves stage (20 May 2015, and 25 May 2016). Glyphosate (isopropylamine salt, 360 g a.i. L−1) was applied at 2880 mL ha−1 (1.39 kg a.i. ha−1). Herbicide was applied with a spraying volume of 250 L ha−1 at 303.97 kPa pressure with a field sprayer, pressurized by a pump, and pulled by a tractor. The sprayer was fitted with flat fan nozzles and had a 12 m working width. Tractor speed during spray was 6 km/h. Prior to treatments (mowing or soil incorporation) of the cover crops, aboveground biomass samples of the cover crops were collected in a randomly selected 50 × 50 cm quadrat in each plot. At the same time, weed biomass was measured by cutting all weeds at ground level in a 50 × 50 cm quadrat placed in each plot. Weeds and cover crops were dried at 105 ◦C for 24 h to obtain dry biomass. To determine the suppressive effects of cover crops, weed species richness and weed density were assessed at 7, 14, and 28 days after treatments (mowing, soil incorporation, herbicide application, or mechanical weed control) from all plots using a 50 × 50 cm quadrat placed randomly in the plots.

2.3. Statistical Analyses Data from each year were analyzed separately because of significant year-by-treatment effects except for the data on weed species richness and weed density. Data were subjected to ANOVA and treatment means were compared using Duncan’s protected LSD tests at the 0.05 probability level. Species richness was calculated using the number of weed species recorded in each plot. Data were transformed as needed before analysis using either arcsine square root or log transformations. Untransformed means were presented in the text for clarity of presentation.

3. Results Dominant weed species in the experimental area in apricot orchard included A. retroflexus, C. arvensis, T. terrestris, Sisymbrium officinale., Sorghum halepense, Lamium amplexicaule L., L., Thlaspi arvense L., and Vaccaria pyramidata MEDIK (Table1). Densities of other weed species such as Lactuca serriola L., Sinapis arvensis L., and Glycyrrhiza glabra Linn. were lower than 1%. Weed counts and weed weights taken in both years showed that A. retroflexus (22%), C. arvensis (16%), Agronomy 2018, 8, 150 4 of 10

T. terrestris (16%), S. officinalis (14%), and S. halepense (7%) contributed over 75% of the total weed populationsAgronomy 2018 (Table, 8, x 1FOR). PEER REVIEW 4 of 10

TableTable 1. Major 1. Major weed weed species species present present in in the the experimental experimental area and and their their relative relative proportion proportion just just before before treatmentstreatments (combined (combined means means of of 2015 2015 and and 2016). 2016).

Weed Species Bayer Code Relative Proportion (%) Weed Species Bayer Code Relative Proportion (%) Amaranthus retroflexus L. AMATR 22 AmaranthusConvolvulus retroflexus arvensisL. L. AMATRCONAR 16 22 Convolvulus arvensis L. CONAR 16 Tribulus terrestris L. TRBTE 16 Tribulus terrestris L. TRBTE 16 SisymbriumSisymbrium officinale officinale(L.) Scop. (L.) Scop. SSYOFSSYOF 14 14 SorghumSorghum halepense halepense(L.) Per. (L.) Per. SORHASORHA 7 7 LamiumLamium amplexicaule amplexicauleL. L. LAMAMLAMAM 3 3 ChenopodiumChenopodium album albumL. L. CHEALCHEAL 3 3 ThlaspiThlaspi arvense arvenseL. L. THLARTHLAR 3 3 VaccariaVaccaria pyramidata pyramidataMedik. Medik. VAAPYVAAPY 3 3 PapaverPapaver rhoeas rhoeasL. L. PAPRHPAPRH 2 2 (L.) Scop. CIRAR 2 Cirsium arvense (L.) Scop. CIRAR 2 Xanthium strumarium L. XANST 1 PortulacaXanthium oleracea strumariumL. L. POROLXANST 1 1 Convolvulus galaticusPortulacaRost. oleracea ex Choisy L. CONGAPOROL 1 1 ConvolvulusAnthemis arvensisgalaticusL. Rost. ex Choisy ANTARCONGA 1 1 AnthemisOthers arvensis L. ANTAR 1 <5 Others <5 Cover crop emergence was similar in 2015 and 2016 growing seasons (data not shown). However, Cover crop emergence was similar in 2015 and 2016 growing seasons (data not shown). significantlyHowever, highersignificantly biomass higher was biomass produced was inproduced 2016 than in 2016 in 2015 than (Figure in 20151 ).(FigureTriticale 1). Triticale+ V. pannonica + V. −1 producedpannonica significantly produced significantly higher biomass higher (6212.5 biomass kg ha(6212.5) than kg ha all−1) other than speciesall other in species 2015. inP. tanacetifolia2015. P. −1 producedtanacetifolia higher produced biomass higher (6511 biomass kg ha (6511) in kg 2016. ha −1 The) in 2016. lowest The cover lowest crop cover dry crop biomass dry biomass was obtained was −1 −1 fromobtainedV. villosa from(2575 V. kg villosa ha (2575) in 2015kg ha and−1) inF. 2015 esculentum and F. esculentum(3440 kg ha(3440) inkg 2016. ha−1) in Statistical 2016. Statistical difference for thedifference quantities for th ofe quantities dry biomass of dry production biomass production by cover by crops cover was crops insignificant was insignificant in 2016. in 2016. The The greater biomassgreater production biomass production in the second in the year second could year be attributedcould be attributed to more to optimal more optimal conditions conditions for growth for of the covergrowth crops. of the cover crops.

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Figure 1. Biomass production (kg ha −1) of cover crops during the year (A) 2015 and (B) 2016. The Figure 1. Biomass production (kg ha−1) of cover crops during the year (A) 2015 and (B) 2016. The columns not sharing a letter in common differ significantly at p < 0.05. columns not sharing a letter in common differ significantly at p < 0.05. The effects of the cover crops on weed dry biomass production just before treatment (mowing or soil incorporation of cover crops) were consistent in each year (Figure 2). In 2015, weed biomass was the highest in the control i.e., without cover crops followed by V. pannonica, Triticale + V.

Agronomy 2018, 8, 150 5 of 10

The effects of the cover crops on weed dry biomass production just before treatment (mowing or soilAgronomy incorporation 2018, 8, x FOR of PEER cover REVIEW crops) were consistent in each year (Figure2). In 2015, weed biomass5 of 10 was the highest in the control i.e., without cover crops followed by V. pannonica, Triticale + V. pannonica, V.pannonic villosaAgronomy, aF., esculentum2018V. , 8 villosa, x FOR, ,PEERP.F. tanacetifolia esculentumREVIEW , , mechanicalP. tanacetifolia weed, mechanical control, and weed herbicide control, applications. and herbicide5 of In10 2016, applications. In 2016, the weed biomass was highest in mechanical control and non -treated parcels the weedpannonic biomassa, V. villosa was highest, F. esculentum in mechanical, P. tanacetifolia control and, mechanical non-treated weed parcels control followed, and by herbicideV. pannonica . followed by V. pannonica. Other treatments (V. villosa, Triticale + V. pannonica, F. esculentum, P. Otherapplications. treatments In ( V.2016, villosa the, weedTriticale biomass+ V. pannonicawas highest, F. in esculentum mechanical, P. control tanacetifolia and non, and-treated glyphosate) parcels had tanacetifolia, and glyphosate) had the lowest and statistically equal weed dry biomass. P. tanacetifolia the lowestfollowed and by statistically V. pannonica equal. Other weed treatments dry biomass. (V. villosaP. tanacetifolia, Triticale + V.was pannonica the most, F. suppressive esculentum, P. species, was the most suppressive species, reducing total weed dry biomass by 83.64% in 2015 and by 53.7% reducingtanacetifolia total, weedand glyphosate) dry biomass had by the 83.64% lowest inand 2015 statistically and by 53.7%equal weed in 2016. dry biomass. P. tanacetifolia in 2016. was the most suppressive species, reducing total weed dry biomass by 83.64% in 2015 and by 53.7% 1200in 2016.A a 1200

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Weed control treatments −2 FigureFigure 2. 2.Effects Effects of of variousvarious living cover cover crops crops on on the the dry dry biomass biomass production production (g m (g) m of− weed2) of weedspecies species −2 duringduringFigure (A(A )2.) 2015 2015Effects and and of ( various (BB) )2016. 2016. livingThe The columns cover columns crops not onsharing not the sharing dry a letterbiomass a letterin common production in common differ (g m significantly differ) of weed significantly species at p < at 0.05. p < 0.05.during (A) 2015 and (B) 2016. The columns not sharing a letter in common differ significantly at p < 0.05. In addition to weed dry biomass reduction by living cover crops, mowed and soil incorporated coverIn additioncropsIn addition also to caused to weed weed a dry decreasedry biomass biomass in weed reductionreduction species by by livingrichness living cover cover (Figures crops, crops, 3mowed and mowed 4). and Data andsoil indicated incorporated soil incorporated that covermowedcover crops covercrops also cropsalso caused caused including a a decrease decrease V. villosa inin, V.weedweed pannonica species , Tritical richness richness + V. (Figures pannonica (Figures 3 ,and 3and and 4). P.4 Data).tanacetifolia Data indicated indicated caused that that moweda significantlymowed cover cover crops higher crops including decreaseincludingV. in V. villosaweed villosa species, ,V. V. pannonicapannonica richness, , TriticalTritical (number) ++ V.V. pannonicathan pannonica untreated, and, and P. control, tanacetifoliaP. tanacetifolia glyphosate causedcaused a significantlyapplication,a significantly highermechanical higher decrease decrease weed incontrol in weed weed, and species species a cover richnessrichness crop F.(number) (number) esculentum than than (Figure untreated untreated 3). Thecontrol, control,effect glyphosate of glyphosatecover application,cropsapplication, was sustainable mechanical mechanical even weed weed after control, control one month, and of a a covermowing cover crop crop (the F.F. dateesculentum esculentum for last (Figure data(Figure recording). 3). The3). Theeffect effect of cover of cover crops was sustainable even after one month of mowing (the date for last data recording). crops was sustainable even after one month of mowing (the date for last data recording). V. villosa V. pannonica Triticale + V. pannonica P. tanacetifoliaV. villosa F.V. esculentum pannonica MechanicalTriticale + V. control pannonica 14 HerbicideP. tanacetifolia ControlF. esculentum Mechanical control 14 a 12 Herbicide Control a 12 a 10 a 10 a 8 a 8 b b b b b 6 b b b 6 bc b b bc bc bc 4 bc bc bcbc bc cd c c c c bcbcbc 4 d d d cd c c bcbcbcbc 2 d d d c c 2 0

Speciesrichness (number) 0 7 14 28 Speciesrichness (number) 7 14 28 Days after mowing of the cover crops Days after mowing of the cover crops

Figure 3. Effect of mowed cover crops, mechanical control, and herbicide application on weed richness Figure 3. Effect of mowed cover crops, mechanical control, and herbicide application on weed (numberFigure of 3. species) Effect of in mowed apricot cover orchard. crops, For mechanical each data control recording, and (7,herbicide 14, or 28 application days), the on columns weed not richness (number of species) in apricot orchard. For each data recording (7, 14, o r 28 days), the richness (number of species) in apricot orchard. For each data recording (7, 14, o r 28 days), the sharingcolumns a letternot sharing in common a letter differin common significantly differ significantly at p < 0.05. at Data p < 0.05. is an Data average is an average of two of years. two years. columns not sharing a letter in common differ significantly at p < 0.05. Data is an average of two years.

Agronomy 2018, 8, 150 6 of 10 Agronomy 2018, 8, x FOR PEER REVIEW 6 of 10

Agronomy 2018, 8, x FOR PEER REVIEW 6 of 10 SoilSoil incorporation incorporation of of cover cover crops crops had had results results similar similar to to mowing mowing on on weed weed suppression suppression in in apricot apricot orchardsorchards (Figure (FigureSoil incorporation4). 4). Mechanical Mechanical of cover weed weed crops control co hadntrol results or glyphosateor glyphosate similar to application mowing application on weed had had asuppression lower a lower effectiveness effectivenessin apricot againstagainst speciesorchards species richness (Figure richness than 4). Mechanicalthan the soil the incorporated soil weed incorporated control cover or glyphosate crops cover i.e., crops applicationP. tanacetifolia i.e., P. had tanacetifolia, V.a lower villosa ,effectiveness,V. V. pannonica villosa , ,V. andpannonicaTriticaleagainst, +andV. species pannonicaTriticale richness +. V.F. esculentumpannonica than the. soilwasF. esculentum incorporated least effective was cover least among cropseffective the i.e., cover amongP. tanacetifolia crops. the cover, V. crops. villosa, V. pannonica, and Triticale + V. pannonica. F. esculentum was least effective among the cover crops. V. villosa V. pannonica Triticale + V. pannonica P. tanacetifolia V. villosa V. pannonica Triticale + V. pannonica P. tanacetifolia F. esculentum Mechanical control Herbicide Control 14 F. esculentum Mechanical control Herbicide Control 14 a a 12 12 aa 10 10 a a 8 8 b b 6 b bb b b bb b 6 bcbc 4 c c bcbc bc 4 bcbc bc bc c c c c c bc 2 d d cc c c c c 2 d dd d c 0d d 0

Speciesrichness (number) 7 14 28

Speciesrichness (number) 7 14 28 Days after soil incorporation of the cover crops Days after soil incorporation of the cover crops

Figure 4. Effect of soil incorporated cover crops, mechanical control, and herbicide application on weed richness (numberFigure 4. ofEffect species) of soil in incorporated apricot orchard. cover For crops, each mechanical data recording control (7,, and 14, herbicide or 28 days), application the column on weed richness (number of species) in apricot orchard. For each data recording (7, 14, or 28 days), the notFigure sharing 4. aEffect letter of in soil common incorporated differ significantly cover crops, at p mechanical< 0.05. Data control is an average, and herbicide of two years. application on column not sharing a letter in common differ significantly at p < 0.05. Data is an average of two years. weed richness (number of species) in apricot orchard. For each data recording (7, 14, or 28 days), the Bothcolumn theBoth covernot thesharing mowingcover a mowingletter and in common soiland soil incorporation incorporationdiffer significantly had had significantly significantlyat p < 0.05. Data decreased decreased is an average the the weed weedof two density years. density in in apricotapricot orchard orchard (Figures (Figure5 ands 5 6and). Among 6). Among the thecover cover crops, crops,F. F. esculentum esculentum (either(either mowed or or soil soil incorporated)Bothincorporated) the had cover the had mowing lowest the lowest effectiveness and soileffectiveness incorporation to decrease to decrease had weed significantlyweed density density in decreased in apricot. apricot. MechanicaltheMechanical weed density weed weed in controlapricot hadcontrol orchard a weed had density (Figurea weed sdensity close 5 and to close control6). toAmong control (weedy) the (weedy) treatment cover treatment cr followedops, F.followed esculentum by glyphosate by glyphosate (either application. mowedapplication. or The soil mostincorporated) effectiveThe most cover hadeffective cropsthe colowest (bothver crops foreffectiveness (both mowing for mowing and to decrease soil and incorporation) soil weed incorporation) density for decreasing infor apricot.decreasingweed Mechanical weed density density weed in in apricot were V. villosa, V. pannonica, P. tanacetifolia, and Tritical + V. pannonica (Figures 5 and 6). apricotcontrol were hadV. a villosa weed, V.density pannonica close, P. to tanacetifolia control (weedy), and Tritical treatment+ V. pannonicafollowed by(Figures glyphosate5 and6 application.). The most effective cover crops (both for mowing and soil incorporation) for decreasing weed density in apricot were V. villosaV. villosa, V. pannonica, P.V. pannonicatanacetifolia, andTriticale Tritical + V. pannonica+ V. pannonicaP. tanacetifolia (Figures 5 and 6).

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Weed density (plantWeed 0 Figure 5. Effect of mowing of cover crops, mechanical control, and herbicide application on weed 7 14 28 density in apricot orchard. For each data recording (7, 14, or 28 days), the columns not sharing a letter

in common differ significantlyDays atafterp < 0.05. mowing Data is o anf the average cover of two crops years.

Agronomy 2018, 8, x FOR PEER REVIEW 7 of 10

Figure 5. Effect of mowing of cover crops, mechanical control, and herbicide application on weed density in apricot orchard. For each data recording (7, 14, or 28 days), the columns not sharing a letter Agronomy 2018, 8, 150 7 of 10 in common differ significantly at p < 0.05. Data is an average of two years.

V. villosa V. pannonica Triticale + V. pannonica P. tanacetifolia

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Figure 6. Effect of soil incorporation of cover crops, mechanical control, and herbicide application on weedFigure density 6. Effect in apricot of soil incorporation orchard. For each of cover data recordingcrops, mechanical (7, 14, or control 28 days),, and the herbicide columns notapplication sharing on a letterweed in density common in differapricot significantly orchard. For at eachp < 0.05. data Data recording is an average (7, 14, or of 28 two days) years., the columns not sharing a letter in common differ significantly at p < 0.05. Data is an average of two years. 4. Discussion 4. Discussion The results of this research work highlighted that cover crops can be effective in reducing the weed The results of this research work highlighted that cover crops can be effective in reducing the density, dry weight, and infestation in apricot orchards. Cover crop plants reduce the development of weed density, dry weight, and infestation in apricot orchards. Cover crop plants reduce the weeds and production by directly competing with weeds for light and nutrients [23–25]. The role development of weeds and seed production by directly competing with weeds for light and nutrients of cover crop plants in decreasing weed density and biomass is due to their physical effects, reduction [23–25]. The role of cover crop plants in decreasing weed density and biomass is due to their physical of light permeability, changes in soil temperature, increase in soil moisture, and allelochemical effects, reduction of light permeability, changes in soil temperature, increase in soil m oisture, and interactions [12,26–29]. The suppressive effects of hairy vetch on weeds have been well-reported allelochemical interactions [12,26–29]. The suppressive effects of hairy vetch on weeds have been previously, and this could suppress the weeds by more than 60% [30,31]. This cover crop (hairy vetch) well-reported previously, and this could suppress the weeds by more than 60% [30,31]. This cover was also effective in suppressing weeds in organically grown lettuce and pepper [32,33]. Cover crops’ crop (hairy vetch) was also effective in suppressing weeds in organically grown lettuce and pepper biomasses were reasonably good to suppress the weeds. Higher cover crop biomass was obtained [32,33]. Cover crops’ biomasses were reasonably good to suppress the weeds. Higher cover crop in the second year of study than the first year. Particularly, during the spring season of the first biomass was obtained in the second year of study than the first year. Particularly, during the spring year of study, there were high rains that supposedly influenced the weeds positively and the cover season of the first year of study, there were high rains that supposedly influenced the weeds crops negatively. positively and the cover crops negatively. In our findings, lacy phacelia was the most effective cover crop that suppressed the weeds by In our findings, lacy phacelia was the most effective cover crop that suppressed the weeds by almost 75%, followed by buckwheat that registered a 73% weed suppression, and hairy vetch with almost 75%, followed by buckwheat that registered a 73% weed suppression, and hairy vetch with a a 63% suppression of weeds. The lowest weed suppression was obtained from the Hungarian vetch 63% suppression of weeds. The lowest weed suppression was obtained from the Hungarian vetch cover crop plants (33%), whereas this effect was over 50% in Hungarian vetch + Triticale mixture. These cover crop plants (33%), whereas this effect was over 50% in Hungarian vetch + Triticale mixture. results are supported by previously reported research work. Previously, lacy phacelia cover crop was These results are supported by previously reported research work. Previously, lacy phacelia cover reported to suppress Echinochloa crus-galli (L.) P.Beauv., C. album, and Portulaca oleracea L. in maize crop was reported to suppress Echinochloa crus-galli (L.) P.Beauv., C. album, and Portulaca oleracea L. plantings [34]. in maize plantings [34]. Efficacy of cover crops against weeds has been reported in the previous literature. For example, Efficacy of cover crops against weeds has been reported in the previous literature. For example, Melilotus officinalis (L.) Pall. as a cover crop in the fallow systems could reduce weed biomass Melilotus officinalis (L.) Pall. as a cover crop in the fallow systems could reduce weed biomass over over 95% and could also suppress the weeds when residues of this cover crop were mixed in the 95% and could also suppress the weeds when residues of this cover crop were mixed in the soil [35]. soil [35]. Although, this much high weed suppression was not obtained in our research, we can safely Although, this much high weed suppression was not obtained in our research, we can safely recommend that cover crop can suppress weeds, particularly in the fruit . Legume cover recommend that cover crop can suppress weeds, particularly in the fruit gardens. Legume cover crops could also add nutrients to soil along with suppressing weeds, and this may play an important crops could also add nutrients to soil along with suppressing weeds, and this may play an important role in conserving the soil and sustaining the agricultural production [36]. We supposed that weed role in conserving the soil and sustaining the agricultural production [36]. We supposed that weed suppression obtained in our studies was a result of both a physical and chemical interference of cover suppression obtained in our studies was a result of both a physical and chemical inter ference of cover crops with weeds. Recent literature establishes that cover crops suppress weeds both by their physical pressure and chemical interactions [11,12,29,37]. Agronomy 2018, 8, 150 8 of 10

Allelopathic potential is one of the factors that help the cover crops to suppress weeds [12,26,38]. Previous literature reports the allelopathic potential of cover crops that have been found effective against weeds [39–42]. For example, Sturm et al. [39] reported that buckwheat caused an allelopathic suppression of Stellaria media (L.) Vill., while palmitic acid gallic acid were described as potent allelochemicals of buckwheat [43]. Allelopathic potential of hairy vetch has also been reported by several researchers [40,41]. Cyanamide was reported as an allelochemical from hairy vetch, which could inhibit the growth of other plants [41,42]. The treatments were maintained in the same fields in the first and the second year of study. Hence, this may had provided time and opportunity to the perennial weeds to get established in the fields, and ultimately the efficacy of mechanical weed control was decreased in the second year of the study. It was observed that perennial weeds such as S. halepense and Cirsium arvense (L.) Scop. had high infestation in the mechanical weed control parcels. The results of this study are important in the wake of problems associated with application of herbicides (such as herbicide resistance evolution in weeds or environmental pollution) and provide an alternative for sustainably controlling weeds in apricot orchards [27,28]. Cover crops tested in this work were generally effective in suppressing weeds in either living, mowed, or soil-incorporated forms. The living form of cover crops had an efficacy lower than glyphosate or mechanical weed control (Figure2). However, these were more effective than glyphosate or mechanical control after mowing or soil incorporation (Figures3–6). From this, we can safely suggest mowing or soil incorporation of living cover crops for increasing their weed suppression efficacy. Nevertheless, along with weed control, the cover crops also play a role in sustaining soil resources (reducing soil erosion, improving soil moisture and organic matter status, etc.) [7]. The results also provide an opportunity for effective non-chemical weed control, and this in turn is important for organic fruit production.

5. Conclusions The results of this study are important in the perspective of organic fruit production. The most important weeds in the experimental area were A. retroflexus, C. arvensis, T. terrestris, S. officinale, and S. halepense. Non-chemical methods such as cover crops could effectively control weeds in the apricot orchard. Among the weed control treatments, the highest weed suppression was obtained with the cover crops including lacy phacelia, buckwheat, hairy vetch and Triticale + Hungarian vetch. Mowing or soil-incorporation of the cover crops were also helpful in suppressing the weeds, and could provide weed control better than the glyphosate application or mechanical weed control.

Author Contributions: Conceptualization, Funding Acquisition, and Methodology: N.T., D.I., and Z.D.; Statistical analysis and Writing: N.T. and K.J. Funding: This research was funded by the Scientific and Technological Research Council of Turkey grant number (Project No. 213 O 109). Acknowledgments: The authors thank the Scientific and Technological Research Council of Turkey (TUBITAK)˙ for the financial support for this project (Project No. 213 O 109). Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

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