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Crop Protection 27 (2008) 101–103

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Managing weeds with drip-applied herbicides in tomato

Bielinski M. Santosa,�, James P. Gilreatha, Marıa de L. Lugob, Luıs E. Riverab

aGulf Coast Research and Education Center, IFAS, University of Florida, 14625 County Road 672, Wimauma, FL 33598, USAbCrop Protection Department, University of Puerto Rico at Mayaguez, Mayaguez, Puerto Rico

Received 4 April 2007; accepted 5 April 2007

Abstract

Field trials were conducted on heavy soils in Puerto Rico and the Dominican Republic to compare the efficacy of herbicide delivery

methods, and to examine the performance of herbicides on weed control in tomato (Lycopersicon esculentum Mill.). Herbicides were

applied either with a piston-pump backpack sprayer or through drip lines. Herbicide treatments were a non-treated control,

S-metolachlor, napropamide, pebulate, and trifluralin. Effects of the herbicide delivery method were not significant for tomato yield,

which indicated that herbicide application through drip lines performed similar to conventional preplant incorporated application. The

highest extra-large and total tomato fruit weight were obtained in plots treated with S-metolachlor, representing 75% and 57%

increments in yields, respectively. These results suggested that in heavy soils, such as the ones in the two locations in Puerto Rico and the

Dominican Republic, application of S-metolachlor through drip lines appears to be an alternative for weed control in tomato fields.

r 2007 Elsevier Ltd. All rights reserved.

Keywords: Lycopersicon esculentum; S-metolachlor; Napropamide; Pebulate; Trifluralin; Application methods

1. Introduction

In the Dominican Republic and Puerto Rico, approxi-mately 10,000 and 300 ha are planted per year with freshmarket tomatoes and processing tomatoes, respectively(Secretarıa de Estado de Agricultura, 2006; US Depart-ment of Agriculture, 2004). In tropical climates, such asthose found in these Caribbean countries, weed manage-ment is a constant challenge for vegetable crop productionbecause of well-distributed rainfall and high temperaturesthroughout the year, favoring intensive weed pressure. Thisis not an exception in tomato fields, where growers rely ona variety of control means to reduce weed interference.Weed species regularly occurring in vegetable crops inthe Caribbean include grasses of the genera Digitaria,Echinochloa, and Eleusine, and the broadleaved generaAmaranthus and Portulaca. These weeds usually grow inrow-middles and through planting holes on plastic mulch.In contrast, Cyperus rotundus L. and C. esculentus L. have

e front matter r 2007 Elsevier Ltd. All rights reserved.

opro.2007.04.012

ing author. Tel.: +1813 633 4128; fax: +1 813 634 0001.

ess: bmsantos@ufl.edu (B.M. Santos).

the ability to penetrate the polyethylene mulch, makingthese species especially problematic to control (Gilreathand Santos, 2004).Currently, backpack and tractor spraying are the most

common herbicide application methods in the Caribbean,both of which require substantial hand labor, equipment,and time, as well as the risk of worker exposure toherbicides. Therefore, devising alternative herbicide deliv-ery methods might be advantageous to growers to reducecosts and exposure. Drip irrigation lines are commonlyused for water, fertilizer, insecticide, and fungicideapplications, but there is no information available onherbicide efficacy with this application method in vegetablecrops.Particularly for tomato production, bare-ground pro-

duction systems employ a combination of mechanized andchemical weed-control methods to control weed emer-gence, whereas in mulched-beds, soil fumigation controlsweed emergence. Improved technology for weed control isneeded in both scenarios. In the first case, MBr is beingphased out in compliance with the Montreal Protocolbecause it is an ozone-depleting molecule (Hildebrand,

ARTICLE IN PRESSB.M. Santos et al. / Crop Protection 27 (2008) 101–103102

2004), while in the second case, cultivation and herbicideshave serious performance limitations to provide season-long weed control. Although MBr alternatives have beenexplored, the majority have poor herbicidal activity; thus,it has been recommended to combine their use with pre-emergence herbicides (Noling and Gilreath, 2002).

The herbicides flazasulfuron, lactofen, halosulfuron,S-metolachlor, metribuzin, napropamide, and pebulatehave been the focus of previous studies. However, variablesuccess has been found with these herbicides. Some of theseherbicides have been tested in diverse vegetable crops. Inbell pepper (Capsicum annuum L.)–cucumber (Cucumis

sativus L.) rotations, the application of the herbicidesnapropamide and S-metolachlor in addition to in-rowinjections of 1,3-D+Pic during the bell pepper seasonprovided excellent control of Eleusine indica (L.) Gaertn.,Digitaria ciliaris (Retz.) Koel., and Amaranthus hybridus

L., but only poor to fair control of Cyperus, during thefollowing cucumber season (Gilreath et al. 2004). In allthese cases, the herbicides were applied either with back-pack or tractor sprayers. The effect of pre-emergenceherbicides on weed populations in tomato must be testedusing drip delivery to assess the potential of this applica-tion method. The objectives of this study were: (a) tocompare the efficacy of herbicide delivery methods and(b) to examine the performance of different herbicides onweed control in tomato.

2. Materials and methods

Two field trials were conducted in a grower’s field inMao, Dominican Republic, and at the Gurabo Experi-mental Station of the University of Puerto Rico atMayaguez, Puerto Rico, during spring 2004. The typicalsoils in both locations are moderate to heavy loamy clays,with organic matter content between 2% and 3%, pHbetween 6.1 and 6.7, and slow infiltration. Herbicides wereapplied either with a piston backpack sprayer (Solo,Newport News, VA) or through drip lines (3.35L/m/hand emitters every 30 cm; T-Tape, T-Systems International,San Diego, CA, USA). Herbicide treatments were a non-treated control, S-metolachlor at a dose of 1.14 kg/ha,napropamide at 2.28 kg/ha, pebulate at 4.56 kg/ha, andtrifluralin at 0.80 kg/ha. Between 3 and 4 weeks beforetransplanting, the backpack-sprayed herbicides were ap-plied with 11,004 flat-fan nozzles and a water volume of520L/ha, and rototilled 10 cm into the soil between,whereas the drip-applied herbicides were delivered with aconventional fertilizer injector (Dosatron Intl., Clearwater,FL, USA) in a volume of approximately 13 L/m2 ofmulched beds. The soil in both locations was not fumigatedto preserve the natural weed populations.

Ten treatments were organized in a split-plot design withsix and four replications in Puerto Rico and the DominicanRepublic, respectively, where herbicide application meth-ods were the main plots and herbicides were distributed inthe subplots. Planting beds were 71 cm on top by 81 cm on

base by 10 cm high and were covered with white on blacklow-density polyethylene mulch (white layer on top).A single drip line was buried on the bed centers beforemulching. ‘Sunny’ tomato plants were transplanted 60 cmapart in single rows and experimental units consisted of 10plants. Other production practices followed local recom-mendations for each location.Weed densities at 7 and 12 weeks after treatment (WAT)

were obtained by counting all emerged species over thearea of each experimental unit and grouped into threeclasses: broadleaved, grasses, and Cyperus. Tomato yieldwas obtained from adding two harvests in each locationand separating in extra-large and total marketable fruitnumber and weight. Resulting data were examined formain effects and interactions between factors with analysisof variance (P ¼ 0.05) and treatment means were separatedwith the Waller–Duncan multiple comparison procedure(SAS Institute, 2000).

3. Results and discussion

The treatment by location interaction was not signifi-cant. There was significant herbicide effect on weeddensities and fruit number and weight, but the effect ofherbicide delivery methods and the herbicide by deliverymethod interaction were not significant, which indicatedthat herbicide application through drip lines performedsimilar to that with the conventional preplant incorporatedapplication method.At 7 WAT, all herbicides were ineffective against

Cyperus, with densities ranging between 2 and 6plants/m2,whereas plots applied with S-metolachlor (0plants/m2),napropamide (1 plant/m2), and pebulate (4 plants/m2)showed the lowest grass densities among all treatments(Table 1). Similarly, S-metolachlor (3 plants/m2) andnapropamide (4 plants/m2) were more effective againstbroadleaved weeds than trifluralin (1 plant/m2), pebulate(14 plants/m2), and the non-treated control (9 plants/m2).At this time, the most predominant broadleaved weedswere Portulaca oleracea L., Trianthema spp., Cleome

viscosa L., Boerhavia erecta L., and Amaranthus dubius

Mart. ex Thell, Echinochloa colona (L.) Link, Digitaria

spp., and E. indica were the most frequent species. Weeddensities at 12 WAT revealed no significant differencesamong treatments on grass and Cyperus control (Table 1).However, the herbicides affected broadleaved weed den-sities, and S-metolachlor application decreased weedpressure to 2 plants/m2, whereas the other herbicides werenot different from the non-treated control, with an averagedensity of approximately 8 plants/m2.The herbicides influenced the number of extra-large and

total marketable tomato fruits. The lowest number ofextra-large fruits (21,250 fruits/ha) was obtained in thenon-treated control plots, which was similar to the valuesobtained with napropamide and pebulate (Table 2). Therewas no difference between the extra-large fruit number inplots treated with S-metolachlor (36,000 fruits/ha) and

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Table 1

Efficacy of pre-emergence herbicides on weed densities at 7 and 12 weeks after treatment (WAT) in tomato

Herbicide Dose (kg/ha) 7 WAT 12 WAT

Broadleaved

(plants/m2)

Grasses

(plants/m2)

Cyperus

(plants/m2)

Broadleaved

(plants/m2)

Grasses

(plants/m2)

Cyperus

(plants/m2)

S-metolachlor 1.14 3b 0 b 2 2 b 3 9

Napropamide 2.28 4b 1 b 6 7 a 6 9

Pebulate 4.56 14a 4 b 4 8 a 5 6

Trifluralin 0.80 10a 6 a 5 7 a 5 8

Control – 9a 6 a 3 9 a 8 5

Significance� �� �� NS �� NS NS NS

Dominican Republic and Puerto Rico, spring 2004.

Values followed by the same letter within each weed type do not differ at the 5% significance level.�Non-significant��Significant at the 5% level.

Table 2

Effect of pre-emergence herbicides on extra-large and total marketable fruit number and weight

Herbicide Dose (kg/ha) Fruit number (number� 1000/ha) Fruit weight (t/ha)

Extra-large Total Extra-large Total

S-metolachlor 1.14 35.0a 70.8a 12.7a 21.4a

Napropamide 2.28 26.3bc 58.3ab 9.1b 16.4b

Pebulate 4.56 24.5bc 55.0ab 8.4b 15.3b

Trifluralin 0.80 29.5ab 59.5ab 9.6b 15.9b

Control – 21.3c 49.5b 7.3b 13.7b

Significance� �� �� �� �� ��

Dominican Republic and Puerto Rico, spring 2004.

Values followed by the same letter within each fruit category do not differ at the 5% significance level.�Non-significant.��Non-significant and significant at the 5% level, respectively.

B.M. Santos et al. / Crop Protection 27 (2008) 101–103 103

trifluralin (29,500 fruits/ha). There were no differencesamong the tested herbicides on tomato fruit number, andfruit production in S-metolachlor-applied plots(70,750 fruits/ha) was the only one significantly differentfrom the fruit number in the non-treated control(49,500 fruits/ha). For tomato fruit weight, the plotstreated with S-metolachlor had the highest values forextra-large (12.7 t/ha) and total marketable weight (21.4 t/ha), which were 75% and 57% higher than the fruit weightobtained in the non-treated control, respectively. Tomatoyield in plots applied with the other herbicides was similarto the yield obtained in the non-treated control plots. Theseresults suggested that in heavy soils, such as the ones in thetwo locations in Puerto Rico and the Dominican Republic,application of S-metolachlor through drip lines appears tobe an effective alternative for weed control in tomato fields.

Acknowledgments

This research was partially supported by the Tropicaland Subtropical Agriculture Research Program (USDA,CSREES).

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