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The efficacy of the reduced rates of 1,3-D + abamectin for control of Meloidogyne incognita in tomato production in China
Scientia Horticulturae 178 (2014) 248–252
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The efficacy of the reduced rates of 1,3-D + abamectin for control of Meloidogyne incognita in tomato production in China Kang Qiao a,∗ , Haiming Duan b , Hongyan Wang c , Yang Wang a , Kaiyun Wang a , Min Wei d,∗ a
College of Plant Protection, Shandong Agricultural University, Tai’an 271018, Shandong, PR China College of Agriculture, Anhui Science and Technology University, Fengyang 233100, Anhui, PR China Cotton Research Center, Shandong Academy of Agricultural Sciences, Jinan 250100, Shandong, PR China d College of Horticulture Science and Engineering, Shandong Agricultural University, Tai’an 271018, Shandong, PR China b c
a r t i c l e
i n f o
Article history: Received 30 June 2014 Received in revised form 20 August 2014 Accepted 23 August 2014 Available online 26 September 2014 Keywords: Efficacy Integrated Management Meloidogyne incognita Vegetables
a b s t r a c t Tomato growers in China commonly face heavy root-knot nematode (Meloidogyne incognita) infestations. Current methods of control rely mainly on methyl bromide (MB) treatments to the soil. Our previous studies demonstrated that 1,3-dichloropropene (1,3-D) and abamectin were feasible alternatives to MB, and both had been widely used. However, the efficacy of reduced rates of 1,3-D combination with abamectin for their potential to control root-knot nematodes and effect on yield remains unknown. In the present study, the efficacy of such combination was tested in laboratory and field conditions. Laboratory tests showed that 1,3-D + abamectin (1:1, volume) exhibited moderate efficacy to M. incognita, better than abamectin used alone, with LC50 and LC90 2.28 and 10.40 mg a.i. L−1 , respectively. In field trials, reduced rates of 1,3-D + abamectin exhibited high control effect on M. incognita and were also associated to higher tomato growth and yield, compared with 1,3-D dose used alone. 1,3-D + abamectin treatment exhibited a better performance than both 1,3-D doses used alone, demonstrating its superiority of combining use. There was a 17.7% to 60.9% and 11.4% and 67.8% yield increase from the various treatments compared with the control in the both seasons. The results of this study demonstrated that reduced rates of 1,3D + abamectin had the potential to be used as an effective alternative to MB for M. incognita control and tomato production in Shandong province, China. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Tomato (Solanum lycopersicum L.) is a major vegetable crop worldwide. In China, more than 1500,000 hectare (ha) of tomato were planted in 2009 and the production reached 34,000,000 tonnes (t), placing China as the world’s largest country both in cultivated area and production (Gao et al., 2011). In recent years, tomato yield losses have been strongly associated with root-knot nematodes of Meloidogyne spp., which cause increased damage in crops grown under intensive regimens (Collange et al., 2011). Root-knot nematodes are globally distributed, attacking over 2000 different plant species and causing high yield losses, particularly in agricultural, silvicultural and horticultural crops (Hanson et al., 2010; Hashem and Abo-Elyousr, 2011). Root-knot nematodes complete part of their life in soil either as eggs or as second-stage juveniles (J2). The latter enter the roots and establish feeding sites
∗ Corresponding author. Tel.: +86 0538 8248596; fax: +86 05388242345. E-mail addresses: [email protected] (K. Qiao), [email protected] (M. Wei). http://dx.doi.org/10.1016/j.scienta.2014.08.018 0304-4238/© 2014 Elsevier B.V. All rights reserved.
in susceptible hosts, inducing root to swell and form root galling. This can drastically limit water and nutrient uptake, leading to severe damage that ultimately is reflected in a significant decline of yield and produce quality (Echeverrigaray et al., 2010). In Shandong province, China, the most common species of root-knot nematodes in greenhouse is Meloidogyne incognita (Kofoid & White) Chitwood (southern root-knot nematode) (Zhao et al., 2003). At present, the standard nematode management practice in many high-value crop production systems is pre-plant soil fumigation with methyl bromide (MB). However, due to its detrimental effects on stratospheric ozone, production and use of MB in developing countries is expected to be totally phased out by 2015 (UNEP, 2006). Because MB is an effective method for pest control, its withdrawal from use as an agricultural fumigant has raised concerns and prompted a great amount of research aimed at finding environmentally acceptable alternatives. As a well-known nematicide, 1,3-dichloropropene (1,3-D) has been registered in many countries and is to be registered in China. Most research about 1,3-D discuss its excellent control of nematodes on different crops (Covarellia et al., 2010; Haydock et al., 2010). Abamectin, a macrocyclic lactone derived from the soil
K. Qiao et al. / Scientia Horticulturae 178 (2014) 248–252
bacterium Streptomyces avermitilis, is another product that is attracting wide interest because of its observed nematicide activity (Faske and Starr, 2006; Monfort et al., 2006). Our previous studies documented the high efficacy of 1,3-D and abamectin to control root-knot nematodes in tomato when applied singly (Qiao et al., 2010, 2012a). However, little is known about the combined effects of both pesticides on the nematodes control and their effect on tomato yield. Moreover, the combination use of 1,3-D + abamectin might be a good practice to reduce application rate of 1,3-D in the field, which would also reduce environmental pollution. Therefore, the aims of the present study were: (a) to determine the efficacy of 1,3-D in combination with abamectin for the control of M. incognita in laboratory tests, and (b) to evaluate M. incognita control and tomato crop productivity with reduced rates of 1,3-D applications with combination of abamectin compared with conventional MB and 1,3-D applied alone at conventional rates in the field. 2. Materials and methods 2.1. Chemicals and nematode inoculum 1,3-D (>98% a.i., Shengpeng Bio-Tech Co., Ltd., Shandong, China) and abamectin (>99% a.i., Chem Service, West Chester, PA) were dissolved in acetone to various concentrations (1.0–200 mg L−1 ). 1,3-D, 92% emulsifiable concentrate, a.i., Shengpeng Bio-Tech Co., Ltd., Shandong, China. Abamectin, 0.5% granules, a.i., Chinese Academy of Agricultural Sciences, Beijing, China. MB, 98% gas, a.i., Lianyungang Dead Sea Bromine compounds Co., Ltd., Jiangsu, China. The M. incognita inoculum was originally isolated from tomato in central Shandong province and maintained in tomato plants in the greenhouse. The classification of this isolate was performed by perineal configuration, esterase electrophoretic pattern, and host range analyses. Eggs were collected from ten-week-old plants with sodium hypochlorite (NaClO) (Hussey and Barker, 1973). Briefly, infected tomato plants were uprooted from soil and the entire root system was dipped in water and washed gently to remove adhering soil. Egg masses of M. incognita were picked with forceps. Egg masses were rinsed with sterile water then placed in 0.5% NaClO solution agitated for 4 minutes and rinsed with sterile water on a 26 m sieve. Second-stage juveniles (J2) were collected in hatching boxes, similar to the modified Jenkins method (Jenkins, 1964). Population density of J2 was determined from 5 replications of 1 mL aliquots of an inoculum suspension for in vitro experiments. Only freshly hatched J2 (24 h old) were used in the experiments. 2.2. Laboratory test The effect of 1,3-D, abamectin and their combination (1:1, volume) on juveniles of M. incognita was determined in aqueous tests. 1,3-D, abamectin and 1,3-D + abamectin treatments were prepared in acetone + distilled water (10:90% volume) at concentrations of 1.0, 5.0, 10, 25, 50, 100 and 200 mg a.i. L−1 . 1 mL from each treatment aqueous solution was added to individual wells of a 24-well plate and another 1 mL containing between 100 and 200 (150 ± 10.6) J2 of M. incognita was added to each well. Each treatment was replicated six times. Plates were wrapped with virtually impermeable film (VIF), placed in plastic bags and stored in aluminum foil pans covered with another pan to keep them under dark. The plates were kept at 25 ◦ C, and nematode activity was evaluated after 48 h of incubation. The inactive nematodes were carefully washed with fresh tap water, collected in a container and evaluated for movement. Nematodes were considered dead when no movement was observed at 40× magnification. To confirm the nematicidal activity of 1,3-D and abamectin, immobile J2 larvae (20 to 30 larvae)
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were collected from the above experiments, transferred to other tissue culture plates filled with water, and monitored for 12 h. The experiments were repeated twice in the laboratory. 2.3. Field trials With the authorization of the institute of Fang country, Tai’an city, Shandong province, China, field trials were established in August of the 2010–2011 and January of the 2011–2012 cropping seasons, respectively, in a commercial greenhouse near Fang country. The soil at the experimental site was a silt loam, composed of 27.3% sand, 69.8% silt and 2.9% clay, with organic matter content 18.5 g kg−1 soil, pH 7.2 and soil bulk density 1.23 g cm−3 . The selected experimental site was planted with tomatoes for the previous 11 years and seriously infested with M. incognita (48 juveniles/10 mL of soil) as determined by the Jenkins method (Jenkins, 1964). Based on previous soil analysis and crop nutritional requirements, the field received a broadcast application of 245 kg ha−1 of 15N-0P-25K as starter fertilizer. Prior to treatment application, the plots were disked twice before bed formation for planting. A randomized complete block design with five replications was used. The treatments were applied once two weeks before planting: (a) MB (98% Gas) as a reference treatment, furrow applied at a dose of 400 kg ha−1 ; (b) 1,3-D (92% EC) furrow applied at a dose of 225 kg ha−1 in combination with abamectin (0.5% Granules) furrow applied at a dose of 225 g ha−1 ; (c) 1,3-D furrow applied at a dose of 150 kg ha−1 combined with abamectin furrow applied at a dose of 225 g ha−1 ; (d) 1,3-D furrow applied at a dose of 225 kg ha−1 ; (e) 1,3-D furrow applied at a dose of 150 kg ha−1 ; (f) abamectin furrow applied at a dose of 225 g ha−1 , and an untreated control. Chemical application rates were based on previous studies and label application directions for field use. Individual plots were 25 m2 in size and consisted of five tomato rows and about 100 tomato plants. Each plot was irrigated separately with 1.3 cm water block to avoid cross contamination the day before fumigation and allow better bedding. In the first season, on the day of fumigation (August 12, 2010), chemicals were furrow applied to the soil 0.25 m deep and 0.50 m apart just on the planting rows, and then the planting rows were bedded and pressed 0.80 m wide at the base, 0.70 m wide at the top, 0.20 m high and spaced 0.75 m apart on centers. Immediately after fumigant application, the beds were pressed and covered with 0.038 mm high-density polyethylene mulch film. Six-week-old ‘Holland No. 6’ tomato seedlings were transplanted into the top of the beds two weeks after treatment (WAT) on September 1, 2010 and on January 30, 2011. Raised beds were 1.5 m apart and each plot contained 20 tomato plants spaced at 0.50 m in the row. Plants were staked and tied as needed during the season. Ordinary flood irrigation was provided according to the water requirements of the crop. 2.4. Data analysis Data from the laboratory tests were analyzed with probit dose response/mortality regression calculated using SPSS probit procedure (SPSS, version 13.0 for Windows, IBM, Chicago, IL). The observed mortality of the J2s was adjusted using Schneider-Orelli’s formula, whereby mortality was calculated as a percentage and adjusted by mortality in the control (solvent only) (SchneiderOrelli, 1947). The equation is: % adjusted mortality = 100 × [(% mortality treated − mortality control)/(100 − mortality control)] (Schneider-Orelli, 1947). Adjusted mortality was used to calculate lethal concentrations required to kill 50% (LC50 ) and 90% (LC90 ) second-stage juveniles. For the field trials, in both tomato growing seasons, plant height was measured from ten plants per plot at 30 and 50 days after
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Fig. 1. Percent mortality of Meloidogyne incognita juveniles (J2) in response to 1,3-D, abamectin, and 1,3-D + abamectin treatments, and lethal concentrations (LC50 and LC90 ; mg L−1 ) of these treatments after 48 h of exposure.
transplanting (DAT). Nematode populations were determined at 20, 40, and 60 DAT by extracting soil samples from the rhizosphere of ten tomato plants per plot and the nematodes were separated by genera and counted from 100 cm3 of soil using a standard sieving and centrifugation procedure (Jenkins, 1964). M. incognita root galling index was determined at 14 WAT by digging the roots of six plants per plot and evaluating root damage using a 0–10 scale, where 0 = no galls, 1 = 0–10% of roots galled,. . . up to 10 = 90–100% of roots galled (Barker et al., 1986). All marketable tomato fruits in each plot were harvested at 12 and 14 WAT (a typical practice in greenhouse production in north China), and graded according to current market standards into the extra-large, large and medium categories. Prior to analysis, data expressed as percentages were arcsine transformed to homogenize variances. The significance of differences between mean values was determined. Analysis of variance (ANOVA) was carried out, and the significance of differences among the treatments was determined according to Fisher’s protected least significant difference (LSD) test (P ≤ 0.05). The field data was analyzed for homogeneity of variances. When the variance was equal, the pooled data of both tests were combined. 3. Results In the laboratory test, 1,3-D, abamectin and their combination (1,3-D + abamectin) caused a high mortality (>90%) of nematode J2 at 25 mg L−1 (Fig. 1). The calculated lethal concentrations required to kill 50% (LC50 ) and 90% (LC90 ) (after 48 h) for J2 were respectively 1.20 and 3.74 mg L−1 for 1,3-D as contrasting to 7.06 and
21.81 mg L−1 for abamectin (Fig. 1). 1,3-D + abamectin exhibited moderate efficacy, better than abamectin used alone, with LC50 and LC90 2.28 and 10.40 mg L−1 , respectively. Furthermore, none of the immobile larvae recuperated their mobility after transfer to water, indicating all treatments had a strong nematicidal activity. In the field trials, almost all treatments significantly improved tomato plant height compared to the untreated controls (Table 1). In the 2010–2011 experiment, the greatest tomato plant heights were observed in plots treated with MB (75.3 cm, 30 DAT and 132.6 cm, 50 DAT, respectively). Other treatments had intermediate height, but were still significantly better than the untreated control. For the 2011–2012 experiment, the MB treatment also resulted in maximum plant height. However, the height of plants treated with 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ) matched those from MB on both sampling dates, better than 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) and both 1,3-D used alone. Moreover, 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) exhibited a better performance than 1,3-D at 225 kg ha−1 , which indicated an advantage of the additional application of abamectin. M. incognita was isolated but other kinds of nematodes were below detectable level. The results confirmed the excellent nematicide activity of 1,3-D. Effects of fumigation programs on plant-parasitic nematode exhibited a similar trend in both seasons. All treatments were effective against M. incognita population levels and root galling index (Table 2). The best results were obtained with the MB and 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ). Tomatoes grown in the untreated plots had the greatest number of nematodes and the highest root galling index. Interesting, the same situation happened again that 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ) matched all those from MB, better than 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) and both 1,3-D used alone. Moreover, 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) exhibited a better performance than 1,3-D at 225 kg ha−1 , which conformed the advantage of additional application of abamectin. All of the treatments increased the marketable tomato yield compared to the untreated control for both seasons. In the first season, there was a 17.7% to 60.9% yield increase from the various treatments compared with the control. In the second season, the yield increase was between 11.4% and 67.8% (Table 3). As in the 2010-2011 experiment, the highest yields of all three categories of fruit were obtained in the MB treatment, while the lowest was achieved in the untreated control. A similar trend was observed for total marketable fruit yield, where the highest yield (128.4 t ha−1 ) was produced in the MB treatment plots, however, the 1,3-D at the dose of 225 kg ha−1 could match those from MB. Yields in 2011–2012 had similar trends as in 2010–2011, with maximum weight of extra-large, large, and medium categories produced in plots treated with MB (Table 3). However, in this growing season, performance of the 1,3-D (225 kg ha−1 ) + abamectin
Table 1 Effect of treatments on height of tomato plants at 30 and 50 days after transplanting in the two growing seasons. Treatment and application ratea
Plant height (cm) 2010–2011 growing season 30 DAT
−1
MB (400 kg ha ) 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (225 kg ha−1 ) 1,3-D (150 kg ha−1 ) Abamectin (225 g ha−1 ) Untreated control a b
b
75.3 a 74.8a 73.9a 67.8b 70.9ab 67.8b 62.5c
2011–2012 growing season 50 DAT
30 DAT
50 DAT
132.6a 131.9a 128.1ab 129.9ab 126.1b 124.5b 120.3c
32.1a 31.9a 31.5a 27.3b 29.9ab 26.4bc 24.0c
82.8a 82.6a 80.4ab 77.6b 78.7b 76.4b 70.4c
Abbreviations: MB = methyl bromide; 1,3-D = 1,3-dichloropropene; DAT = days after transplanting. Values of height in each cell are the arithmetic means of five replications and means separated with LSD test (P = 0.05).
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Table 2 Number of juveniles (J2) of Meloidogyne incognita in the soil at 20, 40 and 60 days after transplanting and root galling in tomato plants in the two growing seasons. Treatmenta
Number of juveniles (J2) 100 cm3 soilb 2010–2011
MB (400 kg ha−1 ) 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (225 kg ha−1 ) 1,3-D (150 kg ha−1 ) Abamectin (225 g ha−1 ) Untreated control
Root galling indexc 2011–2012
20DAT
40DAT
60DAT
20DAT
40DAT
60DAT
0.5d 0.7d 0.9cd 1.2c 1.0c 4.2b 18.3a
1.4c 1.2c 1.1c 1.1c 1.6c 9.5b 25.4a
2.8d 2.5d 2.9cd 3.5c 4.8c 12.8b 35.9a
2.8d 2.4d 3.1cd 3.5cd 6.0 c 15.5b 32.5a
5.3c 4.6c 6.1bc 6.7bc 11.3b 34.5a 41.5a
16.4c 14.3d 17.7bc 19.7bc 26.3b 41.8a 45.4a
2010–2011
2011–2012
0.78d 0.64d 1.05c 1.04c 1.26c 3.52b 4.32a
1.24d 1.02d 1.41c 1.51c 2.82b 7.23a 7.56a
a
Abbreviations: MB = methyl bromide; 1,3-D = 1,3-dichloropropene; DAT = days after transplanting. Number of juveniles (J2) in 100 cm3 soil were determined at 20, 40 and 60DAT in two growing seasons. Data are arithmetic means of five replications and means separated with LSD test (P = 0.05). Values followed by the same letter did not differ at the 5% significance level. c Nematode root galling index collected at 14 weeks after treatment application obtained with a 0–10 scale where 0 = no galls and 10 = 100% of roots galled. Data are arithmetic means of five replications and means separated with LSD test (P = 0.05). b
Table 3 Effect of treatments on tomato marketable yields. Treatmenta 2010-2011 experiment MB (400 kg ha−1 ) 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (225 kg ha−1 ) 1,3-D (150 kg ha−1 ) Abamectin (225 g ha−1 ) Untreated control 2011–2012 experiment MB (400 kg ha−1 ) 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (225 kg ha−1 ) 1,3-D (150 kg ha−1 ) Abamectin (225 g ha−1 ) Untreated control a b
Extra-large (t ha−1 )
Large (t ha−1 )
Medium (t ha−1 )
Marketable (t ha−1 )
15.1ab 14.1a 12.8ab 10.6b 9.5c 9.4c 7.2d
41.2a 38.7ab 35.4b 34.1b 27.0c 26.1d 22.4e
72.1a 69.1a 67.5b 67.2b 58.1c 58.4c 50.2d
128.4a 121.9a 115.7ab 111.9ab 94.6b 93.9b 79.8c
14.3a 13.1ab 11.8b 11.5b 10.7bc 7.9c 6.2d
35.3a 32.7ab 27.8b 26.9b 24.6bc 22.3c 15.2d
63.8a 63.2a 52.5b 49.4b 47b 45.1b 46.2b
113.4a 109.0ab 92.1b 87.8bc 82.3c 75.3cd 67.6d
Abbreviations: MB = methyl bromide; 1,3-D = 1,3-dichloropropene. Numbers in the same column followed by the same letter are not significantly different according to LSD test (P = 0.05).
(225 g ha−1 ) and the MB treatments was similar in all terms. On the other hand, 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) showed good performance on all three categories and total yields, better than the 1,3-D or abamectin used alone. 4. Discussion Efficient and reliable control measures are needed to limit reduction in tomato yields to avoid valuable economic losses for producers. In particular, in modern agriculture, often based on the use of monoculture, the simultaneous control of different plant adversities assumes particular importance. Overall, our results indicated that all treatments had a positive effect on tomato yield, and higher 1,3-D + abamectin dose could reach the same marketable yield level as MB. The results obtained in the present study revealed that 1,3-D + abamectin was effective in suppression of M. incognita while promoting tomato marketable yields. Laboratory test results confirmed that 1,3-D was a feasible alternatives to MB. A wide range of studies that conducted in laboratory and field in various cropping systems had similar results (Covarellia et al., 2010; Qiao et al., 2012b). The observed nematicidal effect of abamectin in this study is in agreement with that of previous studies (Faske and Starr, 2006; Cabrera et al., 2009). The combination of 1,3-D + abamectin might be a choice to reduce application amount of 1,3-D in the field. As is well known, nematicides like 1,3-D are highly toxic to both human health and the environment (Abawi and Widmer, 2000). Many nematicides are
being progressively banned or highly restricted for protecting vegetable production. Thus, the development of alternative control strategies and long-term integrative approaches is urgently needed in order to replace chemical nematicides (Martin, 2003). As a kind of bio-pesticide, abamectin has been evaluated in soil applications, stem injections, root dips, bulb dips and foliar sprays for potential control of plant-parasitic nematodes in several crops (Garabedian and Van Gundy, 1983; Cayrol et al., 1993; Jansson and Rabatin, 1998). Compared with fumigants that are frequently toxic, expensive, and pose considerable environmental risk, abamectin applied as an added measure is an attractive approach to nematode management in tomato due to its convenience and relatively low risk. Based on the field results, 1,3-D treatments were very effective in enhancing plant height in the first growth season, and an additional application of abamectin would enhance its efficacy. In addition, in both seasons, there was no significant phytotoxicity existed in all the tests which confirmed that soil application of these treatments were safe to tomato crop. Interestingly, lower 1,3D + abamectin treatment exhibited a better performance than the higher 1,3-D dose used alone, which demonstrated its great superiority of combining use. Moreover, in terms of the cost, additional application of abamectin, compared with reduced 1,3-D dose, could not only save cost and increase profits, but also reduce environmental risk. Considering the final increasing yields and the cost savings from reducing amount of 1,3-D, using this reduced dosages of 1,3-D + abamectin would improve profits.
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On the issue of the possible underlying mechanisms of combination use of 1,3-D and abamectin, our pyrosequencing results demonstrated that 1,3-D had only a short-term impact on the indigenous soil microbial community and in the later of the treatment, fumigation soils had a richer diversity than that of non-treatment soils (data not show). And abamectin is a natural fermentation product of the soil bacterium S. avermitilis that will also increase the bacteria diversity (Lankas and Gordon, 1989). A more bacteria diversity may be one of the reasons why 1,3-D + abamectin treatment plots had a higher yield. However, in the laboratory test (Fig. 1), which was shown that 1,3-D + abamectin was less effective than 1,3-D alone, contradicting the field experiments. This contradiction could be explained due to the fact that in the laboratory test a fumigant pesticide was mixed with a non-fumigant nematicide, which had totally different properties and could have led to a negative interaction. Moreover, it is just the laboratory results that cannot perfectly represent the results under the field conditions. It is necessary to conduct field trials to evaluate application prospects of 1,3-D + abamectin in China. Currently no single chemical or non-chemical method exhibits the efficacy of MB (Samtani et al., 2011). Although registered and available abroad, some of the regulations to mitigate risks of human exposure are cumbersome and actually limit the utility of 1,3D products. These include extensive buffer zone requirements, personal protective equipment to limit worker exposure, and in California, a cap on the amount of 1,3-D that can be applied in 1 year per township (93 km2 ) to mitigate the potential for chronic exposure. The township cap in California, which varies with the season and method of application, will restrict the availability of 1,3-D as a full replacement for MB (Duniway, 2002). In European, 1,3-D was currently undergoing a resubmission under Annex 1 listing of Directive 91/414/EEC. Furthermore, our results also showed that 1,3-D alone exhibited more excellent performance in the first season. This point was also agreed with previous study (Giannakou and Anastasiadis, 2005). Moreover, in terms of the cost, application of abamectin was lower than MB and 1,3-D. It is in this context that additional abamectin applications were added to evaluate for their potential to control soil nematodes. Research indicates that the future of nematode control will depend more upon integrated techniques that incorporate cultural practices, genetic resistance, and alternative nematicides to keep populations below damaging levels (Zasada et al., 2010). Therefore, it is necessary to combine 1,3-D + abamectin to reach an integrated control and match MB’s efficacy and cost. 5. Conclusion In conclusion, the results of this study suggested that 1,3-D + abamectin was a feasible MB alternative, as well as economically viable and technically feasible. Based on our results, additional application of abamectin with reduced rate of 1,3D treatment would improve the nematode control efficacy and tomato yield. However, our research can be considered as a preliminary study and more detailed studies on its application rate, combination application and planting under field conditions are necessary before it could be recommended as a routine practice for agricultural production in China. Acknowledgements This work was supported by the National Key Technology R&D Program of China (2014BAD05B03).
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Development and reproduction of Bemisia tabaci biotype B on wild and cultivated tomato accessions. Acta Ecol. Sin. 23, 7211–7217 (in Chinese). Garabedian, S., Van Gundy, S.D., 1983. Use of avermectins for the control of Meloidogyne incognita on tomatoes. J. Nematol. 15, 503–519. Giannakou, I.O., Anastasiadis, I., 2005. Evaluation of chemical strategies as alternatives to methyl bromide for the control of root-knot nematodes in greenhouse cultivated crops. Crop Prot. 24, 499–506. Hanson, B.D., Gerik, J.S., Schneider, S.M., 2010. Effects of reduced-rate methyl bromide applications under conventional and virtually impermeable plastic film in perennial crop field nurseries. Pest Manage. Sci. 66, 892–899. Hashem, M., Abo-Elyousr, K.A., 2011. Management of the root-knot nematode Meloidogyne incognita on tomato with combinations of different biocontrol organisms. Crop Prot. 30, 285–292. Haydock, P.P.J., Deliopoulos, T., Evans, K., Minnis, S.T., 2010. Effects of the nematicide 1,3-dichloropropene on weed populations and stem canker disease severity in potatoes. Crop Prot. 29, 1084–1090. Hussey, R.S., Barker, K.R., 1973. A comparison of methods of collecting inocula for Meloidogyne spp., including a new technique. Plant Dis. Rep. 57, 1025–1028. Jansson, R.K., Rabatin, S., 1998. Potential of foliar, dip, and injection applications of avermectins for control of plant-parasitic nematodes. J. Nematol. 30, 65–75. Jenkins, W.R., 1964. A rapid centrifugal-flotation technique for separating nematodes from soil. Plant Dis. Rep. 48, 692. Lankas, G.R., Gordon, L.R., 1989. Toxicology. In: Campbell, W.C. (Ed.), Ivermectin and Abamectin. Springer-Verlag, New York, NY. Martin, F.N., 2003. Development of alternative strategies for management of soilborne pathogens currently controlled with methyl bromide. Annu. Rev. Phytopathol. 41, 325–350. Monfort, W.S., Kirkpatrick, T.L., Long, D.L., Rideout, S., 2006. Efficacy of a novel nematicidal seed treatment against Meloidogyne incognita on cotton. J. Nematol. 38, 245–249. Qiao, K., Jiang, L.L., Wang, H.Y., Ji, X.X., Wang, K.Y., 2010. Evaluation of 1,3dichloropropene as a methyl bromide alternative in tomato crops in China. J. Agric. Food Chem. 58, 11395–11399. Qiao, K., Liu, X., Wang, H.Y., Xia, X.M., Ji, X.X., Wang, K.Y., 2012a. Effect of abamectin on root-knot nematodes and tomato yield. Pest Manage. Sci. 68, 853–857. Qiao, K., Zhu, Y.K., Wang, H.Y., Xia, X.M., Ji, X.X., Wang, K.Y., 2012b. Effects of 1,3dichloropropene as a methyl bromide alternative for management of nematode, soil-borne disease, and weed in ginger (Zingiber officinale) crops in China. Crop Prot. 32, 71–75. Samtani, J.B., Ajwa, H.A., Weber, J.B., Browne, G.T., Klose, S., Hunzie, J., Fennimore, S.A., 2011. Evaluation of non-fumigant alternatives to methyl bromide for weed control and crop yield in California strawberries (Fragaria ananassa L.). Crop Prot. 30, 45–51. 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The efficacy of the reduced rates of 1,3-D + abamectin for control of Meloidogyne incognita in tomato production in China Kang Qiao a,∗ , Haiming Duan b , Hongyan Wang c , Yang Wang a , Kaiyun Wang a , Min Wei d,∗ a
College of Plant Protection, Shandong Agricultural University, Tai’an 271018, Shandong, PR China College of Agriculture, Anhui Science and Technology University, Fengyang 233100, Anhui, PR China Cotton Research Center, Shandong Academy of Agricultural Sciences, Jinan 250100, Shandong, PR China d College of Horticulture Science and Engineering, Shandong Agricultural University, Tai’an 271018, Shandong, PR China b c
a r t i c l e
i n f o
Article history: Received 30 June 2014 Received in revised form 20 August 2014 Accepted 23 August 2014 Available online 26 September 2014 Keywords: Efficacy Integrated Management Meloidogyne incognita Vegetables
a b s t r a c t Tomato growers in China commonly face heavy root-knot nematode (Meloidogyne incognita) infestations. Current methods of control rely mainly on methyl bromide (MB) treatments to the soil. Our previous studies demonstrated that 1,3-dichloropropene (1,3-D) and abamectin were feasible alternatives to MB, and both had been widely used. However, the efficacy of reduced rates of 1,3-D combination with abamectin for their potential to control root-knot nematodes and effect on yield remains unknown. In the present study, the efficacy of such combination was tested in laboratory and field conditions. Laboratory tests showed that 1,3-D + abamectin (1:1, volume) exhibited moderate efficacy to M. incognita, better than abamectin used alone, with LC50 and LC90 2.28 and 10.40 mg a.i. L−1 , respectively. In field trials, reduced rates of 1,3-D + abamectin exhibited high control effect on M. incognita and were also associated to higher tomato growth and yield, compared with 1,3-D dose used alone. 1,3-D + abamectin treatment exhibited a better performance than both 1,3-D doses used alone, demonstrating its superiority of combining use. There was a 17.7% to 60.9% and 11.4% and 67.8% yield increase from the various treatments compared with the control in the both seasons. The results of this study demonstrated that reduced rates of 1,3D + abamectin had the potential to be used as an effective alternative to MB for M. incognita control and tomato production in Shandong province, China. © 2014 Elsevier B.V. All rights reserved.
1. Introduction Tomato (Solanum lycopersicum L.) is a major vegetable crop worldwide. In China, more than 1500,000 hectare (ha) of tomato were planted in 2009 and the production reached 34,000,000 tonnes (t), placing China as the world’s largest country both in cultivated area and production (Gao et al., 2011). In recent years, tomato yield losses have been strongly associated with root-knot nematodes of Meloidogyne spp., which cause increased damage in crops grown under intensive regimens (Collange et al., 2011). Root-knot nematodes are globally distributed, attacking over 2000 different plant species and causing high yield losses, particularly in agricultural, silvicultural and horticultural crops (Hanson et al., 2010; Hashem and Abo-Elyousr, 2011). Root-knot nematodes complete part of their life in soil either as eggs or as second-stage juveniles (J2). The latter enter the roots and establish feeding sites
∗ Corresponding author. Tel.: +86 0538 8248596; fax: +86 05388242345. E-mail addresses: [email protected] (K. Qiao), [email protected] (M. Wei). http://dx.doi.org/10.1016/j.scienta.2014.08.018 0304-4238/© 2014 Elsevier B.V. All rights reserved.
in susceptible hosts, inducing root to swell and form root galling. This can drastically limit water and nutrient uptake, leading to severe damage that ultimately is reflected in a significant decline of yield and produce quality (Echeverrigaray et al., 2010). In Shandong province, China, the most common species of root-knot nematodes in greenhouse is Meloidogyne incognita (Kofoid & White) Chitwood (southern root-knot nematode) (Zhao et al., 2003). At present, the standard nematode management practice in many high-value crop production systems is pre-plant soil fumigation with methyl bromide (MB). However, due to its detrimental effects on stratospheric ozone, production and use of MB in developing countries is expected to be totally phased out by 2015 (UNEP, 2006). Because MB is an effective method for pest control, its withdrawal from use as an agricultural fumigant has raised concerns and prompted a great amount of research aimed at finding environmentally acceptable alternatives. As a well-known nematicide, 1,3-dichloropropene (1,3-D) has been registered in many countries and is to be registered in China. Most research about 1,3-D discuss its excellent control of nematodes on different crops (Covarellia et al., 2010; Haydock et al., 2010). Abamectin, a macrocyclic lactone derived from the soil
K. Qiao et al. / Scientia Horticulturae 178 (2014) 248–252
bacterium Streptomyces avermitilis, is another product that is attracting wide interest because of its observed nematicide activity (Faske and Starr, 2006; Monfort et al., 2006). Our previous studies documented the high efficacy of 1,3-D and abamectin to control root-knot nematodes in tomato when applied singly (Qiao et al., 2010, 2012a). However, little is known about the combined effects of both pesticides on the nematodes control and their effect on tomato yield. Moreover, the combination use of 1,3-D + abamectin might be a good practice to reduce application rate of 1,3-D in the field, which would also reduce environmental pollution. Therefore, the aims of the present study were: (a) to determine the efficacy of 1,3-D in combination with abamectin for the control of M. incognita in laboratory tests, and (b) to evaluate M. incognita control and tomato crop productivity with reduced rates of 1,3-D applications with combination of abamectin compared with conventional MB and 1,3-D applied alone at conventional rates in the field. 2. Materials and methods 2.1. Chemicals and nematode inoculum 1,3-D (>98% a.i., Shengpeng Bio-Tech Co., Ltd., Shandong, China) and abamectin (>99% a.i., Chem Service, West Chester, PA) were dissolved in acetone to various concentrations (1.0–200 mg L−1 ). 1,3-D, 92% emulsifiable concentrate, a.i., Shengpeng Bio-Tech Co., Ltd., Shandong, China. Abamectin, 0.5% granules, a.i., Chinese Academy of Agricultural Sciences, Beijing, China. MB, 98% gas, a.i., Lianyungang Dead Sea Bromine compounds Co., Ltd., Jiangsu, China. The M. incognita inoculum was originally isolated from tomato in central Shandong province and maintained in tomato plants in the greenhouse. The classification of this isolate was performed by perineal configuration, esterase electrophoretic pattern, and host range analyses. Eggs were collected from ten-week-old plants with sodium hypochlorite (NaClO) (Hussey and Barker, 1973). Briefly, infected tomato plants were uprooted from soil and the entire root system was dipped in water and washed gently to remove adhering soil. Egg masses of M. incognita were picked with forceps. Egg masses were rinsed with sterile water then placed in 0.5% NaClO solution agitated for 4 minutes and rinsed with sterile water on a 26 m sieve. Second-stage juveniles (J2) were collected in hatching boxes, similar to the modified Jenkins method (Jenkins, 1964). Population density of J2 was determined from 5 replications of 1 mL aliquots of an inoculum suspension for in vitro experiments. Only freshly hatched J2 (24 h old) were used in the experiments. 2.2. Laboratory test The effect of 1,3-D, abamectin and their combination (1:1, volume) on juveniles of M. incognita was determined in aqueous tests. 1,3-D, abamectin and 1,3-D + abamectin treatments were prepared in acetone + distilled water (10:90% volume) at concentrations of 1.0, 5.0, 10, 25, 50, 100 and 200 mg a.i. L−1 . 1 mL from each treatment aqueous solution was added to individual wells of a 24-well plate and another 1 mL containing between 100 and 200 (150 ± 10.6) J2 of M. incognita was added to each well. Each treatment was replicated six times. Plates were wrapped with virtually impermeable film (VIF), placed in plastic bags and stored in aluminum foil pans covered with another pan to keep them under dark. The plates were kept at 25 ◦ C, and nematode activity was evaluated after 48 h of incubation. The inactive nematodes were carefully washed with fresh tap water, collected in a container and evaluated for movement. Nematodes were considered dead when no movement was observed at 40× magnification. To confirm the nematicidal activity of 1,3-D and abamectin, immobile J2 larvae (20 to 30 larvae)
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were collected from the above experiments, transferred to other tissue culture plates filled with water, and monitored for 12 h. The experiments were repeated twice in the laboratory. 2.3. Field trials With the authorization of the institute of Fang country, Tai’an city, Shandong province, China, field trials were established in August of the 2010–2011 and January of the 2011–2012 cropping seasons, respectively, in a commercial greenhouse near Fang country. The soil at the experimental site was a silt loam, composed of 27.3% sand, 69.8% silt and 2.9% clay, with organic matter content 18.5 g kg−1 soil, pH 7.2 and soil bulk density 1.23 g cm−3 . The selected experimental site was planted with tomatoes for the previous 11 years and seriously infested with M. incognita (48 juveniles/10 mL of soil) as determined by the Jenkins method (Jenkins, 1964). Based on previous soil analysis and crop nutritional requirements, the field received a broadcast application of 245 kg ha−1 of 15N-0P-25K as starter fertilizer. Prior to treatment application, the plots were disked twice before bed formation for planting. A randomized complete block design with five replications was used. The treatments were applied once two weeks before planting: (a) MB (98% Gas) as a reference treatment, furrow applied at a dose of 400 kg ha−1 ; (b) 1,3-D (92% EC) furrow applied at a dose of 225 kg ha−1 in combination with abamectin (0.5% Granules) furrow applied at a dose of 225 g ha−1 ; (c) 1,3-D furrow applied at a dose of 150 kg ha−1 combined with abamectin furrow applied at a dose of 225 g ha−1 ; (d) 1,3-D furrow applied at a dose of 225 kg ha−1 ; (e) 1,3-D furrow applied at a dose of 150 kg ha−1 ; (f) abamectin furrow applied at a dose of 225 g ha−1 , and an untreated control. Chemical application rates were based on previous studies and label application directions for field use. Individual plots were 25 m2 in size and consisted of five tomato rows and about 100 tomato plants. Each plot was irrigated separately with 1.3 cm water block to avoid cross contamination the day before fumigation and allow better bedding. In the first season, on the day of fumigation (August 12, 2010), chemicals were furrow applied to the soil 0.25 m deep and 0.50 m apart just on the planting rows, and then the planting rows were bedded and pressed 0.80 m wide at the base, 0.70 m wide at the top, 0.20 m high and spaced 0.75 m apart on centers. Immediately after fumigant application, the beds were pressed and covered with 0.038 mm high-density polyethylene mulch film. Six-week-old ‘Holland No. 6’ tomato seedlings were transplanted into the top of the beds two weeks after treatment (WAT) on September 1, 2010 and on January 30, 2011. Raised beds were 1.5 m apart and each plot contained 20 tomato plants spaced at 0.50 m in the row. Plants were staked and tied as needed during the season. Ordinary flood irrigation was provided according to the water requirements of the crop. 2.4. Data analysis Data from the laboratory tests were analyzed with probit dose response/mortality regression calculated using SPSS probit procedure (SPSS, version 13.0 for Windows, IBM, Chicago, IL). The observed mortality of the J2s was adjusted using Schneider-Orelli’s formula, whereby mortality was calculated as a percentage and adjusted by mortality in the control (solvent only) (SchneiderOrelli, 1947). The equation is: % adjusted mortality = 100 × [(% mortality treated − mortality control)/(100 − mortality control)] (Schneider-Orelli, 1947). Adjusted mortality was used to calculate lethal concentrations required to kill 50% (LC50 ) and 90% (LC90 ) second-stage juveniles. For the field trials, in both tomato growing seasons, plant height was measured from ten plants per plot at 30 and 50 days after
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K. Qiao et al. / Scientia Horticulturae 178 (2014) 248–252
Fig. 1. Percent mortality of Meloidogyne incognita juveniles (J2) in response to 1,3-D, abamectin, and 1,3-D + abamectin treatments, and lethal concentrations (LC50 and LC90 ; mg L−1 ) of these treatments after 48 h of exposure.
transplanting (DAT). Nematode populations were determined at 20, 40, and 60 DAT by extracting soil samples from the rhizosphere of ten tomato plants per plot and the nematodes were separated by genera and counted from 100 cm3 of soil using a standard sieving and centrifugation procedure (Jenkins, 1964). M. incognita root galling index was determined at 14 WAT by digging the roots of six plants per plot and evaluating root damage using a 0–10 scale, where 0 = no galls, 1 = 0–10% of roots galled,. . . up to 10 = 90–100% of roots galled (Barker et al., 1986). All marketable tomato fruits in each plot were harvested at 12 and 14 WAT (a typical practice in greenhouse production in north China), and graded according to current market standards into the extra-large, large and medium categories. Prior to analysis, data expressed as percentages were arcsine transformed to homogenize variances. The significance of differences between mean values was determined. Analysis of variance (ANOVA) was carried out, and the significance of differences among the treatments was determined according to Fisher’s protected least significant difference (LSD) test (P ≤ 0.05). The field data was analyzed for homogeneity of variances. When the variance was equal, the pooled data of both tests were combined. 3. Results In the laboratory test, 1,3-D, abamectin and their combination (1,3-D + abamectin) caused a high mortality (>90%) of nematode J2 at 25 mg L−1 (Fig. 1). The calculated lethal concentrations required to kill 50% (LC50 ) and 90% (LC90 ) (after 48 h) for J2 were respectively 1.20 and 3.74 mg L−1 for 1,3-D as contrasting to 7.06 and
21.81 mg L−1 for abamectin (Fig. 1). 1,3-D + abamectin exhibited moderate efficacy, better than abamectin used alone, with LC50 and LC90 2.28 and 10.40 mg L−1 , respectively. Furthermore, none of the immobile larvae recuperated their mobility after transfer to water, indicating all treatments had a strong nematicidal activity. In the field trials, almost all treatments significantly improved tomato plant height compared to the untreated controls (Table 1). In the 2010–2011 experiment, the greatest tomato plant heights were observed in plots treated with MB (75.3 cm, 30 DAT and 132.6 cm, 50 DAT, respectively). Other treatments had intermediate height, but were still significantly better than the untreated control. For the 2011–2012 experiment, the MB treatment also resulted in maximum plant height. However, the height of plants treated with 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ) matched those from MB on both sampling dates, better than 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) and both 1,3-D used alone. Moreover, 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) exhibited a better performance than 1,3-D at 225 kg ha−1 , which indicated an advantage of the additional application of abamectin. M. incognita was isolated but other kinds of nematodes were below detectable level. The results confirmed the excellent nematicide activity of 1,3-D. Effects of fumigation programs on plant-parasitic nematode exhibited a similar trend in both seasons. All treatments were effective against M. incognita population levels and root galling index (Table 2). The best results were obtained with the MB and 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ). Tomatoes grown in the untreated plots had the greatest number of nematodes and the highest root galling index. Interesting, the same situation happened again that 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ) matched all those from MB, better than 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) and both 1,3-D used alone. Moreover, 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) exhibited a better performance than 1,3-D at 225 kg ha−1 , which conformed the advantage of additional application of abamectin. All of the treatments increased the marketable tomato yield compared to the untreated control for both seasons. In the first season, there was a 17.7% to 60.9% yield increase from the various treatments compared with the control. In the second season, the yield increase was between 11.4% and 67.8% (Table 3). As in the 2010-2011 experiment, the highest yields of all three categories of fruit were obtained in the MB treatment, while the lowest was achieved in the untreated control. A similar trend was observed for total marketable fruit yield, where the highest yield (128.4 t ha−1 ) was produced in the MB treatment plots, however, the 1,3-D at the dose of 225 kg ha−1 could match those from MB. Yields in 2011–2012 had similar trends as in 2010–2011, with maximum weight of extra-large, large, and medium categories produced in plots treated with MB (Table 3). However, in this growing season, performance of the 1,3-D (225 kg ha−1 ) + abamectin
Table 1 Effect of treatments on height of tomato plants at 30 and 50 days after transplanting in the two growing seasons. Treatment and application ratea
Plant height (cm) 2010–2011 growing season 30 DAT
−1
MB (400 kg ha ) 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (225 kg ha−1 ) 1,3-D (150 kg ha−1 ) Abamectin (225 g ha−1 ) Untreated control a b
b
75.3 a 74.8a 73.9a 67.8b 70.9ab 67.8b 62.5c
2011–2012 growing season 50 DAT
30 DAT
50 DAT
132.6a 131.9a 128.1ab 129.9ab 126.1b 124.5b 120.3c
32.1a 31.9a 31.5a 27.3b 29.9ab 26.4bc 24.0c
82.8a 82.6a 80.4ab 77.6b 78.7b 76.4b 70.4c
Abbreviations: MB = methyl bromide; 1,3-D = 1,3-dichloropropene; DAT = days after transplanting. Values of height in each cell are the arithmetic means of five replications and means separated with LSD test (P = 0.05).
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Table 2 Number of juveniles (J2) of Meloidogyne incognita in the soil at 20, 40 and 60 days after transplanting and root galling in tomato plants in the two growing seasons. Treatmenta
Number of juveniles (J2) 100 cm3 soilb 2010–2011
MB (400 kg ha−1 ) 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (225 kg ha−1 ) 1,3-D (150 kg ha−1 ) Abamectin (225 g ha−1 ) Untreated control
Root galling indexc 2011–2012
20DAT
40DAT
60DAT
20DAT
40DAT
60DAT
0.5d 0.7d 0.9cd 1.2c 1.0c 4.2b 18.3a
1.4c 1.2c 1.1c 1.1c 1.6c 9.5b 25.4a
2.8d 2.5d 2.9cd 3.5c 4.8c 12.8b 35.9a
2.8d 2.4d 3.1cd 3.5cd 6.0 c 15.5b 32.5a
5.3c 4.6c 6.1bc 6.7bc 11.3b 34.5a 41.5a
16.4c 14.3d 17.7bc 19.7bc 26.3b 41.8a 45.4a
2010–2011
2011–2012
0.78d 0.64d 1.05c 1.04c 1.26c 3.52b 4.32a
1.24d 1.02d 1.41c 1.51c 2.82b 7.23a 7.56a
a
Abbreviations: MB = methyl bromide; 1,3-D = 1,3-dichloropropene; DAT = days after transplanting. Number of juveniles (J2) in 100 cm3 soil were determined at 20, 40 and 60DAT in two growing seasons. Data are arithmetic means of five replications and means separated with LSD test (P = 0.05). Values followed by the same letter did not differ at the 5% significance level. c Nematode root galling index collected at 14 weeks after treatment application obtained with a 0–10 scale where 0 = no galls and 10 = 100% of roots galled. Data are arithmetic means of five replications and means separated with LSD test (P = 0.05). b
Table 3 Effect of treatments on tomato marketable yields. Treatmenta 2010-2011 experiment MB (400 kg ha−1 ) 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (225 kg ha−1 ) 1,3-D (150 kg ha−1 ) Abamectin (225 g ha−1 ) Untreated control 2011–2012 experiment MB (400 kg ha−1 ) 1,3-D (225 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) 1,3-D (225 kg ha−1 ) 1,3-D (150 kg ha−1 ) Abamectin (225 g ha−1 ) Untreated control a b
Extra-large (t ha−1 )
Large (t ha−1 )
Medium (t ha−1 )
Marketable (t ha−1 )
15.1ab 14.1a 12.8ab 10.6b 9.5c 9.4c 7.2d
41.2a 38.7ab 35.4b 34.1b 27.0c 26.1d 22.4e
72.1a 69.1a 67.5b 67.2b 58.1c 58.4c 50.2d
128.4a 121.9a 115.7ab 111.9ab 94.6b 93.9b 79.8c
14.3a 13.1ab 11.8b 11.5b 10.7bc 7.9c 6.2d
35.3a 32.7ab 27.8b 26.9b 24.6bc 22.3c 15.2d
63.8a 63.2a 52.5b 49.4b 47b 45.1b 46.2b
113.4a 109.0ab 92.1b 87.8bc 82.3c 75.3cd 67.6d
Abbreviations: MB = methyl bromide; 1,3-D = 1,3-dichloropropene. Numbers in the same column followed by the same letter are not significantly different according to LSD test (P = 0.05).
(225 g ha−1 ) and the MB treatments was similar in all terms. On the other hand, 1,3-D (150 kg ha−1 ) + abamectin (225 g ha−1 ) showed good performance on all three categories and total yields, better than the 1,3-D or abamectin used alone. 4. Discussion Efficient and reliable control measures are needed to limit reduction in tomato yields to avoid valuable economic losses for producers. In particular, in modern agriculture, often based on the use of monoculture, the simultaneous control of different plant adversities assumes particular importance. Overall, our results indicated that all treatments had a positive effect on tomato yield, and higher 1,3-D + abamectin dose could reach the same marketable yield level as MB. The results obtained in the present study revealed that 1,3-D + abamectin was effective in suppression of M. incognita while promoting tomato marketable yields. Laboratory test results confirmed that 1,3-D was a feasible alternatives to MB. A wide range of studies that conducted in laboratory and field in various cropping systems had similar results (Covarellia et al., 2010; Qiao et al., 2012b). The observed nematicidal effect of abamectin in this study is in agreement with that of previous studies (Faske and Starr, 2006; Cabrera et al., 2009). The combination of 1,3-D + abamectin might be a choice to reduce application amount of 1,3-D in the field. As is well known, nematicides like 1,3-D are highly toxic to both human health and the environment (Abawi and Widmer, 2000). Many nematicides are
being progressively banned or highly restricted for protecting vegetable production. Thus, the development of alternative control strategies and long-term integrative approaches is urgently needed in order to replace chemical nematicides (Martin, 2003). As a kind of bio-pesticide, abamectin has been evaluated in soil applications, stem injections, root dips, bulb dips and foliar sprays for potential control of plant-parasitic nematodes in several crops (Garabedian and Van Gundy, 1983; Cayrol et al., 1993; Jansson and Rabatin, 1998). Compared with fumigants that are frequently toxic, expensive, and pose considerable environmental risk, abamectin applied as an added measure is an attractive approach to nematode management in tomato due to its convenience and relatively low risk. Based on the field results, 1,3-D treatments were very effective in enhancing plant height in the first growth season, and an additional application of abamectin would enhance its efficacy. In addition, in both seasons, there was no significant phytotoxicity existed in all the tests which confirmed that soil application of these treatments were safe to tomato crop. Interestingly, lower 1,3D + abamectin treatment exhibited a better performance than the higher 1,3-D dose used alone, which demonstrated its great superiority of combining use. Moreover, in terms of the cost, additional application of abamectin, compared with reduced 1,3-D dose, could not only save cost and increase profits, but also reduce environmental risk. Considering the final increasing yields and the cost savings from reducing amount of 1,3-D, using this reduced dosages of 1,3-D + abamectin would improve profits.
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On the issue of the possible underlying mechanisms of combination use of 1,3-D and abamectin, our pyrosequencing results demonstrated that 1,3-D had only a short-term impact on the indigenous soil microbial community and in the later of the treatment, fumigation soils had a richer diversity than that of non-treatment soils (data not show). And abamectin is a natural fermentation product of the soil bacterium S. avermitilis that will also increase the bacteria diversity (Lankas and Gordon, 1989). A more bacteria diversity may be one of the reasons why 1,3-D + abamectin treatment plots had a higher yield. However, in the laboratory test (Fig. 1), which was shown that 1,3-D + abamectin was less effective than 1,3-D alone, contradicting the field experiments. This contradiction could be explained due to the fact that in the laboratory test a fumigant pesticide was mixed with a non-fumigant nematicide, which had totally different properties and could have led to a negative interaction. Moreover, it is just the laboratory results that cannot perfectly represent the results under the field conditions. It is necessary to conduct field trials to evaluate application prospects of 1,3-D + abamectin in China. Currently no single chemical or non-chemical method exhibits the efficacy of MB (Samtani et al., 2011). Although registered and available abroad, some of the regulations to mitigate risks of human exposure are cumbersome and actually limit the utility of 1,3D products. These include extensive buffer zone requirements, personal protective equipment to limit worker exposure, and in California, a cap on the amount of 1,3-D that can be applied in 1 year per township (93 km2 ) to mitigate the potential for chronic exposure. The township cap in California, which varies with the season and method of application, will restrict the availability of 1,3-D as a full replacement for MB (Duniway, 2002). In European, 1,3-D was currently undergoing a resubmission under Annex 1 listing of Directive 91/414/EEC. Furthermore, our results also showed that 1,3-D alone exhibited more excellent performance in the first season. This point was also agreed with previous study (Giannakou and Anastasiadis, 2005). Moreover, in terms of the cost, application of abamectin was lower than MB and 1,3-D. It is in this context that additional abamectin applications were added to evaluate for their potential to control soil nematodes. Research indicates that the future of nematode control will depend more upon integrated techniques that incorporate cultural practices, genetic resistance, and alternative nematicides to keep populations below damaging levels (Zasada et al., 2010). Therefore, it is necessary to combine 1,3-D + abamectin to reach an integrated control and match MB’s efficacy and cost. 5. Conclusion In conclusion, the results of this study suggested that 1,3-D + abamectin was a feasible MB alternative, as well as economically viable and technically feasible. Based on our results, additional application of abamectin with reduced rate of 1,3D treatment would improve the nematode control efficacy and tomato yield. However, our research can be considered as a preliminary study and more detailed studies on its application rate, combination application and planting under field conditions are necessary before it could be recommended as a routine practice for agricultural production in China. Acknowledgements This work was supported by the National Key Technology R&D Program of China (2014BAD05B03).
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