Evaluation of the Combination of Dimethyl Disulfide and Dazomet as

Article pubs.acs.org/JAFC

Evaluation of the Combination of Dimethyl Disulfide and Dazomet as an Efficient Methyl Bromide Alternative for Cucumber Production in China Liangang Mao,† Dongdong Yan,†,‡ Qiuxia Wang,†,‡ Yuan Li,†,‡ Canbin Ouyang,†,‡ Pengfei Liu,† Jin Shen,† Meixia Guo,†,‡ and Aocheng Cao*,†,‡ †

Department of Pesticides, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Ministry of Agriculture, Beijing 100193, People’s Republic of China ‡ State Key Laboratory for Biology of Plant Disease and Insect Pests, Beijing 100193, People’s Republic of China ABSTRACT: The combination of dimethyl disulfide (DMDS) and dazomet (DZ) is a potential alternative to methyl bromide (MB) for soil disinfestation. The efficacy of DMDS plus DZ in controlling key soilborne pests was evaluated in a laboratory study and in two commercial cucumber greenhouses. Laboratory studies found that all of the combinations had positive synergistic effects on root-knot nematodes, two key soilborne fungi, and two major weed seeds. Greenhouse trials revealed that the combination of DMDS and DZ (30 + 25 g m−2) successfully suppressed Meloidogyne spp. root galling, sharply reduced the colony-forming units of Fusarium spp. and Phytophthora spp. on media, maintained high cucumber yields, and was not significantly different from MB or DMDS alone, but better than DZ alone. All of the chemical treatments provided significantly better results than the nontreated control. The results indicate that the combination of DMDS and DZ is an efficient MB alternative for cucumber production. KEYWORDS: soil fumigation, dimethyl disulfide, dazomet, root-knot nematode, soilborne fungi, weed control

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INTRODUCTION Together with tomato (Lycopersicon esculentum Mill.) and pepper (Capsicum annuum Linn.), cucumber (Cucumis sativus L.) is one of the most important greenhouse crops in northern China. In the protected cultivation of cucumber, soilborne nematodes, fungi, and weeds exhibit a very strong yield-depressing potential. The main factors leading to high pest populations and crop losses are continuous cucumber−tomato rotations or the monocropping of cucumber and two cropping seasons per calendar year.1,2 Methyl bromide (MB) has been widely used for preplant soil fumigation against soilborne nematodes, pathogens, and weeds in northern China. However, MB has to be totally phased out in China by January 1, 2015, due to the detrimental effects on stratospheric ozone.3 The withdrawal of MB from use as an agricultural fumigant has prompted a good deal of research to find effective and economically acceptable alternatives.4 The current registered chemical MB alternatives for cucumber production in China are metham sodium (MNa), fosthiazate, abamectin, and calcium cyanamide (CC). 1,3-Dichloropropene (1,3-D),5−8 dazomet (DZ),7 MNa,5,9 chloropicrin (Pic),9 1,3-D/ DZ,7 1,3-D/Pic,9 and others have also been tested as chemical alternatives to MB for cucumber production in China and other countries in the world. Dimethyl disulfide (DMDS), which has been registered in the United States and other countries, appears to be highly efficient against various nematodes, including Meloidogyne spp., but is less effective on fungal pathogens.10,11 DZ, a methyl isothiocyanate (MITC) generator, is highly effective at controlling a wide range of arthropods, soilborne fungi, nematodes, and weeds, but is less effective against bacteria and root-knot nematodes.11 Therefore, the combination of DMDS and DZ could be useful as a broad© 2014 American Chemical Society

spectrum soil fumigant. There has been much information in the literature on combinations of 1,3-D and Pic,9,10,12−15 MNa and Pic,15 1,3-D and DZ, 7,16 DMDS and Pic,14 and other combinations as MB chemical alternatives. Little information, however, has been reported to date on the combination of DMDS and DZ. Previously, Van Wambeke et al. reported the synergistic activity of combinations of DMDS and Basamid (98% DZ) at reduced dose rates for broad-spectrum soil disinfestation in soil column experiments.17 The following work was initiated to determine and confirm the effects of the combination of DMDS and DZ on nematodes (Meloidogyne spp.), key soilborne fungi (Fusarium spp. and Phytophthora spp.), and weed seeds (Abutilon theophrasti and Digitaria sanguinalis) in laboratory studies. Two greenhouse trials were also designed to evaluate DMDS and DZ combinations as an MB alternative for cucumber production in China.

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MATERIALS AND METHODS

Laboratory Studies. The efficacy of DMDS and DZ, singly and in combination, was studied in the laboratory. At the end of the cucumber crop growth period, soil samples were collected from the top 20 cm of a cucumber greenhouse in Tongzhou, Beijing, where the occurrence of nematodes and soilborne pathogens was severe. The soil was composed of 57.58% sand, 39.02% silt, and 3.40% clay, with an organic matter content of 32.20 g kg−1 soil and pH 7.26. The soil was sieved through a 2 mm mesh and then mixed together thoroughly. The soil moisture was 19.84% (w/w). Particle size analyses were performed using the pipet Received: Revised: Accepted: Published: 4864

March 13, 2014 May 11, 2014 May 12, 2014 May 12, 2014 dx.doi.org/10.1021/jf501255w | J. Agric. Food Chem. 2014, 62, 4864−4869

Journal of Agricultural and Food Chemistry

Article

Table 1. Soil Characteristics at the Experimental Sites site, year

soil moisture (%)

pH (1:2.5)

organic matter (g kg−1)

N/NH4+ (mg kg−1)

N/NO3− (mg kg−1)

available K (mg kg−1)

available P (mg kg−1)

bulk density (g cm−3)

trial I, 2010 trial II, 2012

28.5 31.7

7.87 7.07

27.1 33

29.9 37.2

285.7 388.1

273.8 875.4

438.3 327.7

0.86 0.95

Table 2. Relevant Trial Dates and Some Other Details site

cucumber cultivar

block area (m2)

fumigant application

tarp removal

cucumber transplant

end of trial

preceding crop

trial I, 2010 trial II, 2012

No. 16 Zhongnong No. 16 Zhongnong

3.2 × 5.7 = 18.24 3.2 × 5.6 = 17.92

Aug 5, 2010 July 27, 2012

Aug 27, 2010 Aug 17, 2012

Sept 5, 2010 Aug 28, 2012

Nov 25, 2010 Dec 3, 2012

tomato tomato

were applied as follows: DZ was applied first by mixing with soil at a rate of 25 g m−2, and then DMDS was applied by chemigation at a rate of 30 g m−2. All of the above treatments were covered with PE film. MB was applied between a PE sheet and soil by the hot gas method at a rate of 40 g m−2, and the PE sheet was left on the soil during the fumigation period. Soil temperatures (at 15 cm depth) were monitored only in the plots of DMDS plus DZ treatments using a data logger (XR440 Pocket Data logger, Pace Scientific, America) for the period from fumigant application to tarp removal. Soil fungus populations [colony-forming units (cfu) g−1 soil] were determined after fumigation from soil samples at the depth of 0−20 cm from the soil surface. Soil from each plot was sampled from three spots along the diagonal line in a plot. Root-knot nematode population densities in the soil were determined after fumigation from the depth of 0−20 cm. Soil from each plot was taken from three spots as above. Soil fungi and root-knot nematode populations were determined using the same methods as in the laboratory studies. Cucumber plant height was evaluated at 4 weeks after transplant (WAT) (20 plants per plot). Root galls were assessed at the end of the trials (20 plants per plot). Plants were rated on a 0−4 scale: 0 = 0%, 1 = 1−25%, 2 = 26−50%, 3 = 51−75%, 4 = 76−100% roots galled.4 Cucumber fruit yields were determined after each harvest and summed together at the end of the trials, and the farmer’s income was calculated. Statistical Analyses.7 Laboratory Studies. Nematode mortality was calculated according to the equation

method.18 Organic carbon contents were determined by wet oxidation using the method of Walkley and Black.19 The pH was measured in a 1:2.5 soil to H2O extract. Soil moisture contents were measured by heating in a drying oven at 105 ± 5 °C until mass constancy was reached.20 Six hundred grams of soil was placed into 2.5 L desiccators. Ten Abutilon theophrasti seeds and 15 Digitaria sanguinalis seeds were buried at the depth of about 2 cm in each desiccator.21 The following treatments were applied with three replicates: DMDS alone (20 or 40 mg active ingredient (ai) kg−1 soil), DZ alone (50 or 100 mg ai kg−1 soil), DMDS plus DZ (20 + 50, 20 + 100, 40 + 50, or 40 + 100 mg ai kg−1 soil), and nontreated control. DMDS was injected into the soil by pipet (Eppendorf, Germany) after sowing the weed seeds, and then the desiccators were immediately sealed with a cover. DZ was applied by mixing with soil, then the seeds were sown, and the vacuum dryer was immediately sealed with a cover. The desiccators were placed in incubators at 28 °C for 5 days. The desiccators were opened to release the residual fumigant for a day, and the weed height was then measured with a caliper. Fusarium spp. and Phytophthora spp. were isolated from the soil quantitatively according to methods described by Komada22 and Masago et al.,23 respectively. Root-knot nematodes (Meloidogyne spp.) were extracted from a 100 g subsample on the basis of methods described by Liu.24 Greenhouse Trials. In 2010 and 2012, two demonstration experiments were carried out in greenhouses growing cucumber on a commercial farm in Tongzhou, Beijing, which is an important production area for this vegetable. The farm has grown tomato and cucumber for more than 5 years and is facing problems caused by heavy infestations of root-knot nematode, soilborne fungi, and other pests. Details relevant to the experiments are given in Tables 1 and 2. DMDS 99 TC (Shanghai Yuanji Chemical Co., Ltd., China, containing 99% DMDS), DZ 98 MG (Nantong Shizhuang Chemical Co., Ltd., China, a commercial product containing 98% DZ), and MB 98 TC (Changyi Chemical Plant, China, containing 98% MB and 2% chloropicrin) were used in this study. Polyethylene film (PE) (0.04 mm thick, from Baoding Baoshuo Plastic Co., Ltd., Hebei Province, China) was used as the soil mulch. The treatments were designed as randomized blocks with three replicates (Table 3). MB as a reference treatment, DMDS alone, DZ alone, DMDS plus DZ, and nontreated control were tested. DMDS was applied by chisel injection at a rate of 60 g m−2. DZ was applied by mixing with soil at a rate of 50 g m−2. The DMDS plus DZ treatments

X=

DMDS 99 TC DZ 98 MG DMDS 99 TC + DZ 98 MG MB 98 TC control

rate (g ai m−2)

tarp typeb

60 50 30 + 25

PE PE PE

40 −

PE −

(1)

where X is nematode mortality (%), N1 is the number of dead nematodes, and N2 is the number of live nematodes. The numbers of dead and live nematodes were counted under a dissecting microscope. When nematodes were found to be still, they were touched with a dissecting needle lightly. If they did not move, we considered them dead. Otherwise, we considered them to be living. Corrected nematode mortality was calculated according to the equation Y=

X1 − X 2 × 100 100 − X 2

(2)

where Y is the corrected nematode mortality (%), X1 is the nematode mortality of treatments (%), and X2 is the nematode mortality of the control (%). The efficacy of controlling fungi or weed seeds was calculated according to the equation

Table 3. Experimental Program of the Greenhouse Trials treatmenta

N1 × 100 N1 + N2

application method

Y=

chisel injection soil mixture chemigation + soil mixture gas distribution −

X1 − X 2 × 100 X1

(3)

where Y is the control efficacy on fungi or weed seeds, X1 is the fungal population or weed height in the control, and X2 is the fungal population or weed height in treated plots. The control efficacy of the combination of DMDS and DZ was calculated according to the following equation based on the method described by Colby:25

a

DMDS, dimethyl disulfide; DZ, dazomet; MB, methyl bromide; TC, technical; MG, microgranule. bPE, polyethylene film.

E0 = X1X 2 /100 4865

(4)

dx.doi.org/10.1021/jf501255w | J. Agric. Food Chem. 2014, 62, 4864−4869


4866

a

DMDS, dimethyl disulfide; DZ, dazomet. bE = actual measured control efficacy of the combination. cE0 = expected control efficacy of the combination dCE, combined efficacy; if E − E0 > 0, CE was expressed as +; if E − E0 < 0, CE was expressed as −; if E − E0 = 0, CE was expressed as ±.

+ + + + 50.85 30.19 35.74 8.04 + + + + 54.07 47.03 50.53 42.11 34.22 43.67 42.76 54.58 + + + + 52.79 47.20 45.11 36.79 37.22 48.02 48.56 62.65 + + + + 53.15 45.49 46.35 35.68 30.03 42.65 40.96 58.17

E − E0 E0

48.79 69.81 64.26 91.96 75.64 76.14 94.13 94.76

20.34 23.86 5.87 5.24

+ + + +

75.65 99.65 64.49 92.28 99.64 100.00 100.00 100.00

E CE E − E0 E0 E CE E − E0 E0

76.14 94.76 99.34 100.00 95.98 100.00 100.00 100.00 54.68 68.33 62.58 79.87 88.29 90.70 93.29 96.69

E CE E − E0 E0 E

58.65 98.80 47.60 80.05 91.67 95.46 100.00 100.00 57.13 77.91 52.57 74.66 83.18 88.14 87.31 93.85 20 40 50 100 20 + 50 20 + 100 40 + 50 40 + 100 DMDS DMDS DZ DZ DMDS + DZ DMDS + DZ DMDS + DZ DMDS + DZ control

CEd E − E0 E0c Eb rate (mg ai kg−1 soil)

RESULTS Laboratory Studies. Root-Knot Nematodes. All four tested rates of DMDS plus DZ combination treatments exhibited a positive synergistic efficacy on root-knot nematodes (Table 4), reducing the numbers of Meloidogyne spp. by at least 83.18%. The highest dose tested in our study (40 + 100 mg kg−1) reduced Meloidogyne spp. by 93.85%. Soilborne Fungi. The four tested rates of DMDS plus DZ also showed positive synergistic efficacy on Fusarium spp. and Phytophthora spp. (Table 4). The levels of Fusarium spp. and Phytophthora spp. were reduced by at least 91.67 and 88.29%, respectively. Weed. The four rates of DMDS plus DZ were all synergistic on Abutilon theophrasti and Digitaria sanguinalis (Table 4), reducing the weed levels by at least 95.98 and 99.64%, respectively. Greenhouse Trials. Soil Temperature. Soil temperatures (at 15 cm depth) during fumigation were similar during trial I (in 2010) and trial II (in 2012) (31.1−37.8 and 31.2−39.4 °C, respectively) in the DMDS plus DZ plots. Root-Knot Nematodes. The untreated controls in trial I (in 2010) and trial II (in 2012) were heavily infested by Meloidogyne spp. (Table 5). Meloidogyne spp. levels were significantly higher in the untreated control compared to all fumigant treatments. However, the results of almost all of the fumigant treatments were not significantly different from each other. Nematode levels in all chemical treatments were statistically the same as with MB. The chemical treatments reduced the nematode levels in trials I and II by at least 81.01 and 94.79%, respectively. The DMDS plus DZ combination treatment reduced the nematode levels by 84.46 and 95.83% in trials I and II, respectively; both results were not significantly different from the MB treatment, but significantly different from the untreated control. Soilborne Fungi. The untreated controls were heavily infested by Fusarium spp. and Phytophthora spp. in both trials (Table 5). Fusarium spp. and Phytophthora spp. levels were significantly higher in the untreated control compared to all fumigant treatments (Table 5). All chemical treatments, except for the DZ treatment, reduced Fusarium spp. by at least 90.15 and 95.38% in trials I and II, respectively (Table 5). The DMDS plus DZ treatments reduced Phytophthora spp. by at least 88.66 and 97.61% in trials I and II, respectively (Table 5). The results of the DMDS plus DZ

treatmenta

■

% control efficacy on Abutilon theophrasti

Table 4. Laboratory Studies on the Efficacy of DMDS and DZ Treatments on Root-Knot Nematodes, Soilborne Fungi, and Weed Seeds

where Y is the root galling index, Rx is the root galling scale of the xth plant, r is the highest root galling scale, and x is the total number of plants. Data were analyzed for ANOVA with SAS (SAS, version 8.0 for Windows). Data for soil fungal and nematode populations were transformed as necessary [square root transformations for small numbers (100) for statistical analyses], but all data are reported as nontransformed values. Significant differences among means were determined by Fisher’s LSD test at P = 0.05.26,27

% control efficacy on Phytophthora spp.

(5)

% control efficacy on Fusarium spp.

R1 + R 2 + ... + R x × 100 r×x

% corrected nematode mortality

Y=

% control efficacy on Digitaria sanguinalis

E0 is the expected control efficacy of the combination, X1 is the actual measured control efficacy of the first fumigant, and X2 is the actual measured control efficacy of the second fumigant. E is the actual measured control efficacy of the combination. If E > E0, the combination was synergistic; if E < E0, the combination was antagonistic. Greenhouse Trials. The efficacy of controlling nematode or fungi was calculated according to eq 3. The root galling index was calculated according to the equation

CE

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Article

Table 5. Effects of Soil Fumigation on Numbers of Meloidogyne spp. Recovered from 100 g of Soil and Colony-Forming Units (cfu) of Fusarium spp. and Phytophthora spp. on Selective Media of 1 g from Soil after Fumigation Meloidogyne spp.

Fusarium spp.

Phytophthora spp.

trial

treatmenta

rate (g ai m−2)

tarp typeb

no./100 g

% reduction

cfu/g

% reduction

cfu/g

% reduction

trial I, 2010

DMDS DZ DMDS + DZ MB control

60 50 30 + 25 40 −

PE PE PE PE −

7bc 37b 30b 13b 193a

96.55 81.01 84.46 93.09 −

40bcc 120b 27c 0c 407a

90.15 70.44 93.43 100 −

1380bcc 1847b 573 cd 120d 5053a

72.69 63.45 88.66 97.63 −

trial II, 2012


60 50 30 + 25 40 −

PE PE PE PE −

7b 17b 13b 33b 320a

97.92 94.79 95.83 98.96 −

7c 87b 20bc 0c 433a

98.46 79.98 95.38 100 −

40c 2420b 180c 7c 7540a

99.47 67.91 97.61 99.91 −

a DMDS, dimethyl disulfide; DZ, dazomet; MB, methyl bromide. bPE, polyethylene film. cIn each column, data are means of three replications. Means followed by the same letter are not different (P = 0.05) according to the LSD test.

Table 6. Effect of Fumigation Treatments on the First Yield of Cucumber trial

date

price (¥ kg1−)

treatmenta

rate (g ai m−2)

tarp typeb

yield (kg m−2)

trial I, 2010

Oct 6, 2010

2.2


60 50 30 + 25 40 −

PE PE PE PE −

0.12abc 0.15a 0.08b 0.13ab 0.02c

trial II, 2012

Oct 1, 2012

3.2


60 50 30 + 25 40 −

PE PE PE PE −

0.26a 0.21a 0.20a 0.19a 0.03b

a DMDS, dimethyl disulfide; DZ, dazomet; MB, methyl bromide. bPE, polyethylene film. cIn the column, data are means of three replications. Means followed by the same letter are not different (P = 0.05) according to the LSD test.

Table 7. Effect of Fumigation Treatments on Cucumber Plant Height, Root Galling Index, Yield, and Income trial

treatmenta

rate (g ai m−2)

tarp typeb

plant heightc (cm)

root galling Indexd (%)

g

0.00b 12.50b 0.00b 0.00b 72.50a 0.00b 1.25b 2.50b 0.00b 36.25a

trial I, 2010


60 50 30 + 25 40 −

PE PE PE PE −

152.6b 139.0b 179.5a 170.2a 67.8c

trial II, 2012


60 50 30 + 25 40 −

PE PE PE PE −

168.4bc 157.5c 184.3ab 196.1a 123.6d

g

yielde (kg m−2) g

incomef (¥ m−2)

5.04b 4.52c 5.47b 6.95a 2.63d

11.10bg 9.01c 11.50b 15.68a 5.86d

6.31a 4.94b 6.59a 5.95a 3.48c

19.65a 15.79b 20.52a 18.33ab 11.01c

DMDS, dimethyl disulfide; DZ, dazomet; MB, methyl bromide. bPE, polyethylene film; WAT, weeks after transplant. cCollected at 4 WAT. Collected at the end of the trials. eCollected at each harvest time and summed together at the end of the trials. fCollected at each harvest time and accumulated together at the end of the trials. gIn each column, data are means of three replications. Means followed by the same letter are not different (P = 0.05) according to the LSD test.

a

d

(0.15 kg m−2), although this was not statistically different from most of the other chemical treatments except for the combination, DMDS plus DZ (Table 6). In trial II the highest first cucumber fruit yield was in the DMDS plot (0.26 kg m−2), but this was not statistically different from all of the other chemical treatments (Table 6). Cucumber Plant Height, Root Galling Index, Plant Mortality, Yield, and Income. Fumigation treatments significantly

treatments and MB treatments were not significantly different (Table 5). First Cucumber Fruit Yield. The first cucumber fruit yield varied with fumigation treatment (Table 6). Cucumbers grown in the untreated plots had the lowest first fruit yield (0.02 and 0.03 kg m−2, respectively) in both greenhouse trials (Table 6). This was statistically different from the first yield of all chemical treatments. In trial I, plots treated with DZ had the highest yield 4867



Article

fungi. The combined use of DMDS and DZ for broad-spectrum soil fumigation, therefore, was at least theoretically feasible. Laboratory studies found that the four tested rates of DMDS plus DZ all had positive synergistic effects on root-knot nematodes (Meloidogyne spp.), two key soilborne fungi (Fusarium spp. and Phytophthora spp.), and two major weed seeds (Digitaria sanguinalis and Abutilon theophrasti). The specific synergistic mechanism of DMDS plus DZ was not clear to us; however, the above laboratory results gave a preliminary indication of the feasibility of their combined application and also confirmed the synergistic activity of combinations of DMDS plus DZ reported by Van Wambeke.17 Our greenhouse trials revealed that the combination of DMDS plus DZ applied to the greenhouse at the rate of 30 + 25 g m−2 successfully suppressed Meloidogyne spp. root galling, sharply reduced the colony-forming units (cfu) of Fusarium spp. and Phytophthora spp. on media, maintained high cucumber yields, and was not significantly different from MB at the dose of 40 g m−2. The results of DMDS plus DZ were statistically similar to those of DMDS alone (at the dose of 60 g m−2), but better than those of DZ alone (at the dose of 50 g m−2). The above greenhouse results also confirmed that the combination of DMDS plus DZ is a good alternative to MB. The simultaneous application of MNa and halogenated fumigants (e.g., Pic and 1,3-D) was found to accelerate the degradation of halogenated fumigants, reducing their availability in soil.33,34 However, the combined application of DMDS plus DZ did not exhibit degradation according to the positive synergistic effects observed from the different rates tested in our laboratory. It has been reported that relatively high application rates may possibly mask degradation;4 however, both high and low rates were tested in our laboratory studies. In both trials, DZ alone showed lower efficacy in controlling soilborne fungi (Table 5) and a lower yield and income than the other fumigant treatments (Table 7) and gave significantly lower results than the DMDS plus DZ combination treatment and the MB treatment. However, in both trials DZ provided a high first yield of cucumber (Table 6), although this was not significantly different from other chemical treatments. The reason could be attributed to a stronger initial plant vigor resulting from the DZ treatment, whereas the DMDS plus DZ and MB treatments produced a higher yield by the end of the season because they reduced more soilborne fungi, and this effect could also be seen in the plant height at the end of both trials (Table 7). In summary, the fumigant combination of DMDS plus DZ was generally as effective as MB in terms of controlling the numbers of soilborne fungi and nematodes and increasing cucumber yields and farmers’ income. However, more detailed work on its precise application method (formulations and so on) is necessary before the combination is recommended as an efficient MB alternative for cucumber production in China.

affected cucumber plant height at 4 WAT (Table 7) in the two greenhouse trials. Cucumber height was significantly higher in all chemical treatments compared with the untreated control. In both trials, the highest cucumber height was observed in plots treated with the DMDS plus DZ and MB treatments. Plant heights in all DMDS plus DZ treatments were taller than those in plots where DMDS and DZ were used alone, except for DMDS treatment in trial II (Table 7). Nematode infestation was evaluated at the end of the trials by calculating the root galling index. Cucumbers grown in the untreated plots had the highest root galling indices (72.50 and 36.25% in trials I and II, respectively). The root galling index of each fumigant treatment was significantly different from the untreated control; however, there were no significant differences among the chemical treatments (Table 7). Cucumber yield varied with the fumigation treatment (Table 7). Cucumbers grown in the untreated plots had the lowest yields (2.63 and 3.48 kg m−2, respectively, in trials I and II) compared to the chemical treatments. In trial I, the highest cucumber yield was observed in plots treated with MB (6.95 kg m−2), followed by DMDS plus DZ, DMDS, and DZ. The DMDS plus DZ cucumber yield was statistically the same as that of DMDS alone, but significantly higher than that of DZ. In trial II, plots treated with DMDS plus DZ produced the highest yield (6.59 kg m−2), which was not significantly different from the MB and DMDS treatments, but significantly higher than for DZ alone and the untreated control. Similarly, the farmer’s income from cucumber production differed with fumigation treatment (Table 7). Cucumbers grown in the untreated plots provided the lowest income in both trials (5.86 and 11.01 ¥ m−2, respectively). In trial I, the plots treated with MB gave the highest income (15.68 ¥ m−2), followed by DMDS plus DZ, DMDS, and DZ. The DMDS plus DZ yield was statistically the same as that of DMDS alone, but significantly higher than that of DZ. In trial II, the plots treated with DMDS plus DZ gave the highest income (20.52 ¥ m−2) followed by those of DMDS, MB, DZ, and the untreated control and were statistically the same as that of DMDS and MB treatments, but significantly higher than those of other treatments.

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DISCUSSION It has been reported that no single chemical or nonchemical method can exhibit the efficacy of MB currently.28 However, three major alternatives for preplant soil treatment (1,3-D/Pic, Pic, and MNa) either alone or in combination with other alternatives are proving as effective as MB in many situations and continue to be widely adopted as key alternatives in many applications.14 On the basis of our greenhouse results, the combination of DMDS plus DZ was as effective as MB in terms of increasing cucumber yields and income. Root-knot nematode control with DMDS has been demonstrated to be as good as with MB in China and elsewhere,10,11,29 and our present laboratory studies and greenhouse trials both confirmed this. However, most DMDS formulations have poor activity against soilborne fungi and ordinary activity against weeds, and both factors were also confirmed in our laboratory studies and greenhouse trials. DMDS therefore requires additional herbicidal and fungicidal activity to improve the control of weeds and soilborne fungi. DZ, a granular MITC generator, was reported to effectively control various soilborne pests (fungi, nematodes, soil insects, and weeds).30−32 Through our laboratory studies, we found that DZ had high activity against weeds and ordinary activity against nematodes and soilborne

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AUTHOR INFORMATION

Corresponding Author

*(C.A.) Mail: Department of Pesticides, Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, People’s Republic of China. Phone: +8610-62815940. Fax: +8610-62894863. E-mail: [email protected]. Funding

This research was supported by the Program on Substituted Technology for Methyl Bromide in China (Special Finance of Chinese Ministry of Agriculture, 2110402) and UNDIO Project on Phasing-out of Methyl Bromide in Agriculture Sector in China (TF/CPR-A/08/003). 4868



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Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank Dr. Melanie Miller for editing the manuscript. REFERENCES

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