Journal of Crop Improvement Brassicaceae Cover ...

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Brassicaceae Cover-Crop Effects on Weed Management in Plasticulture Tomato a

Sanjeev K. Bangarwa & Jason K. Norsworthy

a

a

Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, Arkansas, USA Published online: 28 Mar 2014.

To cite this article: Sanjeev K. Bangarwa & Jason K. Norsworthy (2014) Brassicaceae Cover-Crop Effects on Weed Management in Plasticulture Tomato, Journal of Crop Improvement, 28:2, 145-158, DOI: 10.1080/15427528.2013.858381 To link to this article: http://dx.doi.org/10.1080/15427528.2013.858381

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Journal of Crop Improvement, 28:145–158, 2014 Copyright © Taylor & Francis Group, LLC ISSN: 1542-7528 print/1542-7536 online DOI: 10.1080/15427528.2013.858381

Brassicaceae Cover-Crop Effects on Weed Management in Plasticulture Tomato

Downloaded by [University of Tennessee, Knoxville] at 23:13 07 May 2014

SANJEEV K. BANGARWA and JASON K. NORSWORTHY Department of Crop, Soil, and Environmental Sciences, University of Arkansas, Fayetteville, Arkansas, USA

Weed control options are limited in plasticulture vegetables in the absence of methyl bromide. Field and laboratory studies were conducted to test the efficacy of soil amendment with Brassicaceae cover crops in combination with low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulches for weed control in fresh-market tomato ( Solanum lycopersicum). Three Brassicaceae cover crops, ‘Seventop’ turnip ( Brassica rapa), ‘Pacific Gold’ oriental mustard ( Brassica juncea), and ‘Caliente’, a blend of brown mustard ( Brassica juncea) and white mustard ( Sinapis alba), were tested along with methyl bromide for yellow nutsedge ( Cyperus esculentus) and johnsongrass ( Sorghum halepense) control in tomato. Glucosinoate (GSL) analysis indicated that ‘Caliente’ mustard, ‘Pacific Gold’ oriental mustard, and ‘Seventop’ turnip produced GSLs totaling 26,399, 16,798, and 18,847 µmol m−2 , respectively, prior to termination. The VIF mulch was neither effective in increasing weed control nor in improving tomato yield over LDPE mulch. Regardless of mulch type, Brassicaceae cover crops provided marginal control of yellow nutsedge (≤39%) and johnsongrass (≤46%) at 2 weeks after transplanting (WATP). Moreover, weed control in cover-crop plots declined to ≤20% at ≥4 WATP. Soil amendment with Brassicaceae cover crops did not injure tomato plants. Although soil amendment improved weed control and marketable yield over fallow plots, none of the amended plots produced marketable yield equivalent of methyl bromide (59 t ha−1 ). Therefore, soil amendment with Brassicaceae cover crops cannot be used as a practical alternative to methyl bromide, but it can be Received 18 June 2013; accepted 19 October 2013. Address correspondence to Sanjeev K. Bangarwa, Department of Crop, Soil, and Environmental Sciences, University of Arkansas, 1366 W. Altheimer Dr., Fayetteville, Arkansas 72704, USA. E-mail: [email protected] 145

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S. K. Bangarwa and J. K. Norsworthy

combined with other strategies in an integrated pest management program. KEYWORDS allelopathy, biofumigation, biological weed control, integrated weed management, methyl bromide alternative


INTRODUCTION Soil fumigation with methyl bromide has been a common practice for controlling a wide array of soil-borne pests, including weeds, in plasticulture vegetable production (Duniway 2002). In a commercial production system, methyl bromide is injected pre-plant into the soil and covered with a low-density polyethylene (LDPE) mulch. Plastic mulch is used to minimize gaseous losses of methyl bromide and thereby maximize efficacy against pests. However, LDPE mulch is not completely impermeable and gaseous losses of methyl bromide escape into the atmosphere. As a result, methyl bromide causes stratospheric ozone-depletion and therefore is being phased out of U.S. agriculture and is only available in limited quantity under critical use exemption (U.S. Environmental Protection Agency 2008). Weed management will be challenging for tomato producers in the absence of methyl bromide. Plastic mulches suppress some weeds by providing a physical barrier and by altering light quantity and quality as well as increasing the heat beneath the mulch. However, purple nutsedge (Cyperus rotundus) and yellow nutsedge (Cyperus esculentus) species can readily puncture the plastic mulches (Patterson 1998). In addition, an underground network of tubers and rhizomes makes nutsedge species the most difficult-to-control weeds and a major cause of significant yield reduction in vegetable crops (Morales-Payan et al. 1996, 1997a, 1997b, 1998; Santos et al. 1998; Webster 2005a, b; Bangarwa et al. 2008). Therefore, methyl bromide alternatives are urgently needed. One cultural alternative is biofumigation, which is basically suppression of soil-borne pests by naturally produced allelopathic volatile compounds (Gimsing and Kirkegaard 2009). Examples of such volatile compounds are isothiocyanates (ITCs) produced by Brassicaceae plants. Plants belonging to the Brassicaceae family contain a variety of glucosinolates (GSLs) in their cell vacuoles, which on enzymatic hydrolysis are converted into ITCs (Brown and Morra 1995). The ITCs are biocidal compounds that are inherently volatile and therefore can serve as a fumigant (Brown and Morra 1995, 1996). The simplest form of ITC is methyl ITC, which is the active ingredient in the commercial fumigant Vapam (AMVAC 2011). The ITCs reportedly reduce yellow nutsedge emergence and shoot growth in purple and yellow nutsedge (Norsworthy and Meehan 2005b; Norsworthy et al. 2006).


Brassica Covers crops for weed control in tomato

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In another study, soil amendment with wild radish (Raphanus raphistrum), a Brassicaceae weed, reduced yellow nutsedge tuber production in amended soil (Norsworthy and Meehan 2005a). In the Pacific Northwest, soil amended with rapeseed (Brassica napus) successfully reduced weed biomass up to 96% in the following potato (Solanum tuberosum) crop (Boydston and Hang 1995). Malik et al. (2008) reported that soil amendment with wild radish combined with half the label rates of herbicides could provide optimum large crabgrass (Digitaria sanguinalis) control in sweet corn (Zea mays). Similarly, incorporation of Brassicaceae green manure into soil before planting a commercial crop supplemented herbicidal control of johnsongrass (Uremis et al. 2009). Therefore, soil amendment with Brassicaceae crops can provide a competitive advantage to the preceding crop by suppressing weeds early in the season. The magnitude of weed suppression from soil amendment is dependent upon the concentration and toxicity of ITCs released in treated soil and the length of exposure of ITCs to target weed species (Teasdale and Taylorson 1986). However, the high volatility of ITCs makes them vulnerable to gaseous losses from amended soils under field conditions (Brown and Morra 1996; Peterson et al. 2001; Morra and Kirkegaard 2002). Volatilization losses of ITCs in the field can be minimized by covering the amended soil with lowpermeability plastic mulches immediately after tissue incorporation (Price et al. 2005). Under laboratory experiments, virtually impermeable film (VIF) mulch was more effective than LDPE mulch in reducing methyl ITC losses from the treated soil (Austerweil et al. 2006). Therefore, VIF mulch may provide higher retention of ITCs and in turn improve weed control over LDPE mulch. The objective of this research was to evaluate the weed control in plasticulture tomato using biofumigation from Brassicaceae cover crops under LDPE or VIF mulches and compare it with a standard methyl bromide program.

MATERIALS AND METHODS Location and Soil Type Weed control potential of Brassicaceae cover crops was evaluated in field and laboratory experiments conducted in 2007 at the Arkansas Agricultural Research and Extension Center at Fayetteville, Arkansas. The soil at the field test site was a silt loam (fine-loamy, mixed, active, non-acid) with 1.7% organic matter content and a pH of 6.1. The test site was fallow in 2006 but was tilled twice in spring and fall. The test site contained a natural population of yellow nutsedge and johnsongrass. It was thoroughly tilled in mid-March to remove any vegetation and prepare a smooth seedbed for cover crop planting.

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Experimental Design The experiment was organized in a split-plot design with four replications. Main plots consisted of two mulch types, LDPE and VIF, and the subplot consisted of fallow (nontreated), methyl bromide, and three cover crops: ‘Seventop’ turnip, ‘Pacific Gold’ oriental mustard, and ‘Caliente’ mustard. A standard treatment of methyl bromide included a mixture of methyl bromide (67%) and chloropicrin (33%) applied at 390 kg ha−1 .


Trial Procedure All cover crops were drill-seeded in 7.6-m-long plots with an 18-cm-row spacing. Seeding rate varied with individual cover crop: 5.6 kg ha−1 for ‘Seventop’ turnip and 9 kg ha−1 for ‘Pacific Gold’ oriental mustard and ‘Caliente’ mustard. The fertilization program included pre-plant incorporation of 40 kg ha−1 of nitrogen (N) followed by a top dressing of 40 kg ha−1 N and 30 kg ha−1 sulfur (S) at 5 weeks after planting (WAP). Cover crops received no additional irrigation other than rainfall (total monthly precipitation was: March, 102 mm; April, 130 mm; and May, 100 mm). No pest management practices were followed in cover crops. At 50%–80% pod-fill stage, all the cover crops were flail mowed and incorporated into the top 7.5 cm of the soil using a roto-tiller. Prior to mowing, cover crop densities were recorded by randomly placing 0.5-m2 quadrat in each cover-crop plot. Subsequently, cover-crop shoots and roots were harvested from this 0.5-m2 area and freeze-dried for biomass and GSL quantification. Immediately after incorporation, 70-cm wide raised beds were formed on 1.8-m centers and covered with a black LDPE mulch or black/white VIF mulch using a tractor-mounted plastic layer. Simultaneously, a single row of drip tape was placed in the bed center under the plastic mulch. Treatments were separated by cutting the plastic and covering with soil to avoid volatile ITC movement across the treatments. Similarly, raised beds were formed and covered with plastic mulch in fallow plots. Weed densities were taken in fallow (untreated) plots before forming beds. Averaged across eight plots, the untreated checks had 68 shoots/m2 of yellow nutsedge and 3 plants/m2 of johnsongrass. Transplant holes were punched in the plastic 1 wk following incorporation of cover crops and laying of plastic mulch. A single row of seven ‘Amelia’ tomato transplants (5 wk old) was planted into beds at 60-cm spacing. Additional methyl bromide treatments were applied under LDPE and VIF mulches at 3 weeks prior to transplanting. Standard production and management practices were followed as recommended for drip-irrigated fresh-market plasticulture tomatoes (Holmes and Kemble, 2010). Bare-ground row-middles between the beds were kept clean by directed application of S-metolachlor (Dual Magnum 7.62 EC) and paraquat (Gramoxone Inteon 2 EC).

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Data Collection Weed control and crop injury were visually rated at 2, 4, and 6 WATP on a 0 to 100 scale, where 0 = no injury to crop or no weed control and 100 = crop death or complete weed control. Visual injury rating was taken by evaluating all tomato plants in each plot or bed. Visual weed control rating was taken from central 7-m length of the plot or bed (70-cm wide bed). Visual ratings were based on symptoms, such as chlorosis, necrosis, and stand loss and stunting of tomato or weeds. In addition, tomato fruit-yield data were recorded based on seven tomato harvests from whole plot during the season. Tomato fruits were harvested and graded into six categories (jumbo, extralarge, large, medium, small, and culls) based on USDA standards for fresh market tomato (U.S. Department of Agriculture 1997). For GSLs analysis in shoots and roots of each cover crop, freeze-dried cover crop tissues were ground to powder and passed through a 1-mm screen. In laboratory experiment, GSLs from 0.3-g freeze-dried tissue were extracted and analyzed by high-performance liquid chromatography according to published procedures (Gardiner et al. 1999, Norsworthy et al. 2007).

Statistical Analysis Mean values and associated standard errors of means were calculated for biomass and GSL content for each cover crop. Data on crop injury, weed control, and tomato yield were subjected to analysis of variance with a splitplot structure using PROC GLM in SAS (version 9.2; SAS Institute, Cary, NC). Whole-plot treatment (two mulch type levels) was considered in a randomized complete block, and cover crops/fumigants were the split-plot factor (five levels). Treatment means were separated by Fisher’s protected LSD at α = 0.05.

RESULTS AND DISCUSSION Cover Crop Biomass Prior to terminatin, ‘Caliente’ mustard, ‘Pacific Gold’ oriental mustard, and ‘Seventop’ turnip produced a total dry biomass of 695 (± 59.1), 707 (±71.3), and 584 (±52.1) g m−2 , respectively. Total biomass production in each cover crop was mainly contributed by shoot biomass, which ranged from 88% to 90% of the total biomass (data not shown). In previous cover crop studies, total biomass produced by ‘Caliente’ mustard, ‘Pacific Gold’ oriental mustard, and ‘Seventop’ turnip ranged from 272 to 752 g m−2 , 670 to 920 g m−2 , and 598 to 684 g m−2 , respectively (Hartz et al. 2005; Norsworthy et al. 2005; Bangarwa et al. 2011a). This variation in biomass production in previous trials could be attributed to variation in agronomic and environmental

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conditions, time of establishment (fall vs. spring), and stage of termination of the cover crop.


Glucosinolate Production The type and amount of GSL varied among cover crops as well as between shoots and roots of each cover crop (Table 1). Three types of aliphatic [(2R)-2-hydroxybut-3-enyl, 2-propenyl, and but-3-enyl] and three types of aromatic GSLs (p-hydroxybenzyl, benzyl, and 2-phenylethyl) were detected in either shoots or roots of Brassicaceae cover crops. The major shoot GSL in ‘Caliente’ and ‘Pacific Gold’ mustards was 2-propenyl, whereas benzyl and 2-phenylethyl were dominant shoot GSLs in ‘Seventop’ turnip. In ‘Caliente’ mustard roots, 2-propenyl, p-hydroxybenzyl, and 2-phenylethyl were dominant GSL, whereas 2-propenyl was major root GSL in ‘Pacific Gold’ mustard. ‘Seventop’ turnip roots contained a high amount of 2-phenylethyl GSL. Total GSL concentration in the shoots was 2.8- and 2.6-fold higher than that in roots of ‘Caliente’ mustard and ‘Pacific Gold’ mustard, respectively (Table 1). Conversely, root GSL concentration was 2.8-fold higher than that of the shoot in ‘Seventop’ turnip. However, total GSL production per unit area was mainly contributed by the shoot GSLs because 88 to 90% of total biomass was contributed by shoots (Table 1). Total (shoot plus root) GSL production per unit area for ‘Caliente’ mustard, ‘Pacific Gold’ oriental mustard, and ‘Seventop’ turnip was estimated to be 26,399, 16,798, and 18,847 μmol/m2 , respectively (Table 1). In previous studies, total GSL content in ‘Caliente’ mustard, ‘Pacific Gold’ oriental mustard, and ‘Seventop’ turnip varied from 8,600 to 26,700 μmol m−2 , 9,800 to 11,300 μmol m−2 , and 12,365 to 22,844 μmol m−2 , respectively (Hartz et al. 2005; Norsworthy et al. 2005; Bangarwa et al. 2011b).

Weed Control There was no significant main effect of mulch type or any cover crop by mulch interaction for yellow nutsedge and johnsongrass control at any rating. However, weed control was influenced by the main effect of cover crop/fumigant (Table 2), indicating that VIF mulch did not improve weed control over LDPE mulch in fallow, cover crop, and methyl bromide plots. Thus, VIF mulch was no more effective than LDPE mulch in retaining higher concentration of ITCs in treated soil and providing effective weed control. In previous research, VIF mulch failed to increase methyl ITC retention compared with an LDPE mulch (El Hadiri et al. 2003). Likewise, Haar et al. (2003) tested methyl ITC efficacy against little mallow (Malwa parviflora L.) seeds under VIF and standard mulch and found that viable seed density of little mallow was not statistically different under standard and VIF mulch. In another study, Bangarwa et al. (2011c) reported that herbicidal efficacy of allyl ITC was not improved by replacing LDPE mulch with VIF mulch.

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y

z

8.1 (0.1) 7.6 (0.1) nd 0.6 (0.1) 6.0 (0.1) 22.2 (0.3)

9.2 (0.3) nd nd nd 0.3 (0.1) 9.6 (0.3)

nd

25.1 (1.3) nd 0.2 ( < 0.05) nd 0.3 ( < 0.05) 25.6 (1.4)

25.1 (0.9) 7.3 (2.6) nd 5.8 (0.2) 1.8 (0.8) 40.0 (3.2) nd

nd

nd

μmol g−1

Pacific Gold’ mustard

Standard error of each mean is included in parenthesis. nd = non-detected.

Root (2R)-2-hydroxybut-3enyl 2-propenyl p-hydroxybenzyl But-3-enyl Benzyl 2-phenylethyl Total

Shoot (2R)-2-hydroxybut-3enyl 2-propenyl p-hydroxybenzyl But-3-enyl Benzyl 2-phenylethyl Total

Plant part and glucosinolate type

‘Caliente’ mustard

nd nd nd 10.8 (0.4) 61.1 (2.0) 75.7 (2.6)

3.8 (0.1)

nd nd nd 10.9 (0.7) 13.4 (9.8) 27.2 (9.6)

2.9 (0.2)

‘Seventop’ turnip

622.3 (5.8) 583.3 (7.3) nd 42.6 (4.3) 462.9 (8.4) 1711.0 (25.8)

nd

15484.3 (546.7) 4518.1 (1602.7) nd 3553.7 (120.4) 1131.8 (472.4) 24688.0 (1980.4)

nd

‘Caliente’ mustard

762.3 (27.1) nd 4.0 (3.2) nd 27.1 (6.3) 793.3 (24.8)

nd

15682.1 (818.2) nd 126.6 (10.9) nd 196.2 (23.7) 16004.9 (850.4)

nd

μmol m−2

Pacific Gold’ mustard

nd nd nd 656.1 (23.1) 3726.6 (124.2) 4616.9 (155.8)

234.3 (8.7)

nd nd nd 5695.8 (356.5) 7017.7 (51.7.5) 14230.2 (5018.4)

1516.6 (102.6)

‘Seventop’ turnip

TABLE 1 Type and concentration of glucosinolates detected in the shoot and root tissues of Brassicaceae cover crops and estimated glucosinolates production per unit area prior to termination of cover cropszy .


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df 3 1 4 4 ∗∗∗

NS

NS

∗∗∗

4 WATP NS NS

2 WATP NS NS

Yellow nutsedge (% control)

∗∗∗

NS

6 WATP NS NS ∗∗∗

2 WATP 98 a 38 bc 46 b 34 c 0d

NS

2 WATP NS NS

∗∗∗

4 WATP 96 a 26 b 26 b 22 b 0c

Johnsongrass (% control)

NS

4 WATP NS NS

Johnsongrass (% control)

, ∗∗ , ∗∗∗ denote significance at the 5%, 1%, and 0.1% probability levels, respectively. NS denotes not significant. Treatment means within a column followed by the same letter are not different based on Fisher’s protected LSD at P