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Modifying the formulation of abamectin to promote its efficacy on southern root-knot nematode (Meloidogyne incognita) under blending-of-soil and root-irrigation conditions Beixing Li, Yupeng Ren, Da-xia Zhang, Shuangyu Xu, Wei Mu, and Feng Liu J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b04146 • Publication Date (Web): 14 Dec 2017 Downloaded from http://pubs.acs.org on December 18, 2017

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Journal of Agricultural and Food Chemistry

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Modifying the formulation of abamectin to promote its efficacy on southern

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root-knot nematode (Meloidogyne incognita) under blending-of-soil and

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root-irrigation conditions

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Beixing Li,1,2# Yupeng Ren,1,3# Da-xia Zhang,1,2 Shuangyu Xu,3 Wei Mu,2,3 Feng

5

Liu1,3*

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1. Shandong Provincial Key Laboratory for Biology of Vegetable Diseases and Insect

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Pests, College of Plant Protection, Shandong Agricultural University, Tai’an,

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Shandong 271018, P. R. China

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2. Research Center of Pesticide Environmental Toxicology, Shandong Agricultural

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University, Tai’an, Shandong 271018, China

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3. Key Laboratory of Pesticide Toxicology & Application Technique, Shandong

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Agricultural University, Tai’an, Shandong 271018, P. R. China

13

#

B. Li and Y. Ren share joint first authorship.

14

*

To whom correspondence should be addressed. Tel.: +86 0538-8242611.

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E-mail address: [email protected] (F. Liu).

1

ACS Paragon Plus Environment


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Abstract

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The southern root-knot nematode (RKN), Meloidogyne incognita, is the most

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disastrous and prevalent nematode threat to the production of crops, especially

19

vegetables. In the current study, second-stage juveniles (J2) of M. incognita were

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collected from five regions near Tai’an, China. The toxicity of abamectin to these J2

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had insignificant differences, with LC50 values of approximately 2 mg/L. Two

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pesticide application approaches (i.e., blending-of-soil and root-irrigation) were

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adopted in pot experiments; blending-of-soil was more beneficial for promoting the

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efficacy of abamectin on the RKN of tomatoes. Abamectin microcapsule suspension

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(MCs) exhibited superiority to emulsifiable concentrate (EC) at dosages of 5 and 10

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mg active ingredient per plant integrating efficacy, root length, plant height, the fresh

27

weight of roots and the fresh weight of stems+leaves. Adsorption, leaching and

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mobility of abamectin in the soil also verified bioactivity test results. Modifying the

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formulation of abamectin can promote its efficacy on RKN under different application

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approaches.

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Keywords: Meloidogyne incognita; abamectin; efficacy; formulation; adsorption;

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leaching

2


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Introduction

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Root-knot nematodes, Meloidogyne spp., are wide spread and have caused great

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losses to various cash crops

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Meloidogyne incognita) is the most disastrous and prevalent nematode that threatens

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the production of crops, especially vegetables

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L.), one of the most important greenhouse cash crops in northern China, are cultivated

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worldwide

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adjustment of planting structures in China. Disease caused by M. incognita is also

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aggravated in tomatoes due to successive cropping, appropriate temperature and

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humidity under protective cultivation 11. Various agricultural, physical and biological

43

strategies have been proposed to control phytoparasitic nematodes, including crop

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rotation, flooding treatment and predacious fungi

45

difficult to popularize in China. The use of chemical nematicides is still the primary

46

control method due to its advantages in cost, convenience and universality.

9-10

1-4

. Among them, southern root-knot nematode (RKN,

5-8

. Tomatoes (Solanum lycopersicum

. In recent years, the cultivated area of tomatoes has increased with the

12-18

. However, these measures are

47

Pre-plant soil fumigation with methyl bromide was once the standard treatment

48

for the management of nematodes in many cash crop production systems. However,

49

methyl bromide is no longer available to growers under current regulatory pressure

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due to its detrimental effects on stratospheric ozone

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manufacturers propose to use alternatives, such as 1,3-dichloropropene, calcium

52

cyanamide and methyl isothiocyanate, these chemicals have strong impact on

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beneficial organisms in the soil 20-22. They also have low selectivity and phytotoxicity

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risks to the crops

19

. Although scholars and

23

. Currently registered non-fumigation chemical nematicides in 3



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China include abamectin, fluopyram, fosthiazate, carbosulfan and ethoprophos.

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Among them, abamectin is the most widely used, highly efficient, secure and

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economical nematicide that possesses favorable contact and stomach toxicity 24, 25. Its

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mechanism of action was to suppress the nerve conduction of target creatures by

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releasing abundant γ-aminobutyric acid (GABA)

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extensively reported and registered to control RKN in recent years. Both of abamectin

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emulsifiable concentrate and microcapsule suspension showed favorable efficacies in

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controlling RKN in pot experiments 28. However, in previous experiments, we found

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that the efficacy of abamectin in controlling the RKN of tomatoes differed greatly in

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different experimental fields. We speculate that the following factors may result in

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this phenomenon: (ⅰ) the sensibility of M. incognita to abamectin and (ii) the

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approaches of applying pesticides.

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26, 27

. Abamectin has been

Broadcasting (generally granules), furrow application and root-irrigation are 28

68

commonly used approaches to control RKN

. Application approaches significantly

69

affect the distribution of pesticides and lead to differing control efficacies 29. Control

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efficacy is also greatly influenced by whether pesticides can be maintained for long

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periods at the position where targeted nematodes primarily gather. Therefore, it is

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necessary to develop scientific application techniques for the better utilization of

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nematicides, and labor-saving strategies are still urgently required.

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In the current study, the toxicity of abamectin to second-stage juveniles (J2) of M.

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incognita collected from different regions was initially determined. Then, pot

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experiments were used to evaluate the efficacy of abamectin with different 4


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formulations under different application approaches. The adsorption, leaching and

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mobility of abamectin with different formulations in the soil were also investigated.

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Materials and methods

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Nematodes

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M. incognita was originally isolated from tomato plants in Dongdawu village (Tai’an,

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P.R. China, 117.13 E, 35.98 N, at an altitude of 101 m above mean sea level), liuyi

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farm (Dezhou, China, 116.79 E, 36.91 N, at an altitude of 21 m above mean sea level),

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Kangzhuang village (Dezhou, China, 116.78 E, 36.94 N, at an altitude of 20 m above

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mean sea level), Caosi village (Jinan, China, 117.27 E, 37.13 N, at an altitude of 18 m

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above mean sea level) and Lujiazhuang village (Laiwu, China, 117.57 E, 36.23 N, at

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an altitude of 180 m above mean sea level) and was maintained on tomato plants

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(cultivar Weiba 0) in the greenhouse. Growth conditions in the greenhouse were

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25±2 °C, 70% relative humidity and a 16:8 h light:dark period in 25-cm plastic pots.

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Plants used for inoculations were approximately 50 days old. Eggs of M. incognita

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were extracted from the infected roots of tomatoes with a 1% sodium hypochlorite

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solution

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25±1 °C in darkness 31. Finally, the hatched J2 were counted for further use.

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Pesticides and reagents

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Abamectin technical material (purity = 98%) was provided by the Shandong New

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Power Bio-technology Co. Ltd. (Shandong, China). Abamectin 2% emulsifiable

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concentrate (EC), abamectin 2% suspension concentrate (SC) and abamectin 5%

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microcapsule suspension (MCs) were provided by the Key Laboratory of Pesticide

30

. J2 were collected daily after placing eggs in water and incubating at

5



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Toxicology & Application Technique of Shandong, China. Specially, the MCs were

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prepared via interfacial polymerization with the wall material of polyurea. In addition,

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they owned an average diameter of 3.50 µm and a spherical morphology. Acetonitrile,

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methanol and acetone were all purchased from the Tianjin Yongda Chemical Reagent

103

Co. Ltd. (Tianjin, China).

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Toxicity tests of abamectin to M. incognita collected from different regions

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The standard protocol used is described as follows

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technical material was accurately weighed. Then acetone was added until the mixture

107

totalled 100 ml to yield a stock solution (concentration of 10000 mg/L) for further

108

experiments. Distilled water containing 0.1% Tween-80 was used to dilute the stock

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solution. Then, 1 ml of nematode suspension (a total of approximately 100 M.

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incognita J2) was introduced into each cell in a 24-cell culture plate and mixed with 1

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ml of the diluted solutions. Subsequently, the plates were placed in an incubator at

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25 °C (dark treatment) 31. J2 mortality was assessed after 24 and 48 h. The criterion

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for death was that a J2 did not move during an observation period of 10 s and

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remained immobile 24 h after nematodes were rinsed in water by replacement of

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pesticide solutions with distilled water several times at the same temperature

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exposed to an acetone solution with the same concentration served as a control. To

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enhance experimental precision, each treatment was repeated four times.

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Pot experiments

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Nematode-infected soil used for pot experiments was gathered from greenhouses in

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Dongdawu village (Tai’an, P.R. China, 117.13 E, 35.98 N, at an altitude of 101 m

32

. First, 1.0204 g abamectin

32, 33

. J2

6


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above mean sea level). The soil was determined to be silt loam, composed of 24.26%

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sand, 56.78% silt and 18.96% clay and 17.2 g/kg of organic matter with a pH of 5.6.

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The cultivar of tomato seedlings used for all pot experiments was Jinpeng 11-8.

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Application approaches used in the current study were blending of soil and

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root-irrigation. Abamectin EC, SC and MCs were applied to the soil at the dosage of

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10, 5 or 1 mg active ingredient per plant, respectively. Water treatment was regarded

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as a control, and each treatment was repeated 15 times. Detailed handling methods

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can be found in the Supporting Information. The growth conditions for tomatoes were

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investigated 55 days after transplanting. At the same time, the RKN infection was

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ranked using a 0-10 index according to previously reported methods 32.

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Adsorption of abamectin in the soil

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Adsorption experiments were performed according to a previous report 34. First, 10 g

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of sieved soil (60-mesh) was accurately weighed and transferred to a 250-ml conical

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flask with a stopper. Then, 100 ml of dilutions containing abamectin was added to

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yield initial concentrations (C0) of 0.5, 1, 5 and 10 mg/L. After batch equilibrium on a

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shaker for 24 h (25 ± 2 °C, in darkness), the obtained suspension was transferred to a

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100-ml centrifugal tube. Subsequently, the suspension was centrifuged at 4000 r/min

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for 5 min, and 0.8 ml of the supernatant was removed to mix with 0.8 ml acetonitrile

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for further detection. The mixture was cleaned using a PSA solid phase extraction

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(SPE) cartridge and filtered with a 0.22-µm organic filter prior to the detection of the

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equilibrium concentration Ce (accuracy information can be found in the Supporting

142

Information). To enhance experimental precision, measurements were repeated in 7



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triplicate. Finally, the adsorbing capacity of the soil was calculated using the

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following equation 35: Cs=(C0-Ce) × V0/Ms

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where Cs is the adsorbing capacity (mg/kg); C0 and Ce are the initial and equilibrium

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concentrations (mg/L) of abamectin; and V0 and Ms are the volume (L) of added

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water and weight (kg) of the soil. The adsorption ratio was determined as the ratio of

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abamectin in the soil to that in water.

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Leaching and mobility of abamectin in soil

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Leaching experiments were then performed

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chromatography and soil column leaching tests were adopted to fully clarify the

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leaching and mobility of abamectin in the soil. Detailed information about soil

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column leaching test was elaborated as follows. At first, 700-750 g of sieved soil (2

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mm mesh) was weighed and transferred to a 5 cm × 35 cm plastic tube to yield a

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30-cm high soil column. The column was pre-saturated with 0.01 mol/L CaCl2

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solution after approximately 1 cm height of silica sand was added to the upper layer

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of the soil column. Then, 10 mg (active ingredient) of abamectin with different

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formulations was added dropwise onto the silica sand using a peristaltic pump.

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Subsequently, the soil column was eluted with a total of 300 ml of 0.01 mol/L CaCl2

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solution at a constant flow rate of 30 ml/h. After leaching test, the soil column was

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evenly separated into six parts. Finally, the content of abamectin in each part was

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determined using an UPLC-MS/MS system (detailed operating parameters can be

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found in the Supporting Information). Detailed information for soil thin layer

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chromatography was elaborated as follows. At first, 30 g of sieved soil (0.25 mm

36

,

and both soil thin layer

8


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mesh) was accurately weighed and transferred to a 150-ml beaker. Then

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approximately 22 ml of distilled water was added to generate a homogeneous slurry.

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Subsequently, the slurry was evenly smeared onto a 10 cm × 20 cm glass plate and

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dried in a shaded place. Dilutions containing abamectin were added at 1.5 cm from

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one end. After the water evaporated, the plate was placed in a saturation tank (a

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chromatographic solution of distilled water; liquid height of 0.5 cm; angle of 30

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degrees; 23±2 °C). When the developing solvent reached a distance of 18 cm from the

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original point, the glass plate was dried and evenly divided into six parts. Finally, the

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content of abamectin in each part was determined using an UPLC-MS/MS system and

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the relative shift (Rf) values were also calculated.

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Data analysis

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Data analysis was performed with DPS software (version 7.05). Control efficacy was

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first arcsine transformed, and then subjected for analysis of variance. Differences

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among the treatments were tested using the LSD multiple range test (α = 0.05).

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Results and analysis

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Toxicity of abamectin to M. incognita collected from different regions

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As Table 1 shows, the toxicity of abamectin to J2 of M. incognita collected from

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different regions showed little difference. LC50 and LC90 values for all treatments

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decreased with exposure duration, however, most of the differences were insignificant

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as the 95% confidence limits largely overlapped. Among the five sampling sites,

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abamectin showed the highest toxicity to J2 of M. incognita collected from 9



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Lujiazhuang (Laiwu city), with a 24 h-LC50 value of 1.70 mg/L, whereas that of

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Dongdawu (Tai’an city) had the lowest toxicity (24 h-LC50 value of 4.76 mg/L). The

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toxicity of abamectin to the J2 of M. incognita changed in the following order:

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Lujiazhuang, Laiwu > Kangzhuang, Dezhou > Liuyi farm, Dezhou > Caosi, Jinan >

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Dongdawu, Tai’an.

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Application approaches and formulation influence the efficacy of abamectin on

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the RKN of tomato in pot experiments

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As depicted in Figure 1, both application approaches and formulations of abamectin

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influenced the control efficacy on the RKN of tomato. When the blending-of-soil

196

approach was adopted, EC and MCs treatments exhibited slightly higher control

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efficacy than the SC group, but there were no significant differences (Figure 1a). The

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control efficacy of all treatments increased with the dosage of abamectin. Control

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efficacy increased from approximately 40% to 65% when the dosages of abamectin

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ranged from 1 to 10 mg active ingredient per plant. Apparently, control efficacy was

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positively related to dosage, but far from the dosage-response relationship. The

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control efficacies of root-irrigation groups were obviously lower than those of the

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blending-of-soil groups, especially at dosages of 1 and 5 mg per plant (Figure 1b).

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The results were similar to that for blending-of-soil, except that MC treatment at a

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dosage of 5 mg per plant exhibited significantly higher control efficacy compared to

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the EC and SC treatments. The efficacy discrepancy of EC and SC under different

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application methods may be attributed to the adsorption and leaching of abamectin in

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the soil. 10


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Application approaches and formulation of abamectin influence the growth of

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tomatoes in Pot experiments

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In terms of tomato growth, four indexes were investigated, including root length,

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fresh weight of roots, plant height and the fresh weight of stems and leaves. As shown

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in Figure 2a and b, the root length of EC groups dropped dramatically with the

214

dosage of abamectin, whereas that of SC and MC groups increased gradually

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regardless of the application approaches adopted. In particular, MC groups had the

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longest root length under blending-of-soil conditions, reaching 17.49, 17.92 and 19.43

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cm at dosages of 1, 5 and 10 mg active ingredient per plant. The fresh weight of roots

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exhibited similar tendencies, except that the root weight of EC groups was highest at

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5 mg per plant and lowest at 1 mg per plant under root-irrigation conditions (Figure

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S1a and S1b). The plant height of the EC and SC groups was maintained at

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approximately 37 and 40 cm with the increase in abamectin dosage under

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blending-of-soil conditions, whereas that of MCs groups significantly soared from

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35.73 to 41.28 cm (Figure 2c). In regard to root irrigation, the plant height of all

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treatments increased with abamectin dosage (Figure 2d). Treatments of SC 10 mg

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and MCs of 5 and 10 mg per plant had the highest plant height (approximately 44 cm).

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As illustrated in Figure S1c, the fresh weight of stems and leaves for EC groups were

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approximately 20.5 g at any dosage of abamectin under blending-of-soil conditions,

228

whereas those for the SC and MCs groups dramatically increased. Distinct from

229

blending-of-soil, the fresh weight of stems and leaves of all treatments under

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root-irrigation conditions increased with abamectin dosage (Figure S1d). 11



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Adsorption of abamectin with different formulations in soil

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The adsorption of abamectin with different formulations in the soil was listed in Table

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2. When abamectin was added at the initial concentrations of 0.5-10 mg/L, the

234

concentrations of the EC, SC and MC groups after adsorption equilibrium were

235

measured as 0.034-0.603, 0.070-1.231 and 0.072-1.514 mg/L. The EC groups had the

236

highest adsorption ratios, whereas the MC group’s values were lowest.

237

Leaching of abamectin with different formulations in the soil columns

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As depicted in Figure 3, the distribution of abamectin with different formulations in

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the soil columns differed greatly. All three formulations containing abamectin were

240

primarily maintained at a depth of 0-5, 5-10 and 10-15 cm, especially 0-5 cm in the

241

soil columns. Moreover, the mass fraction of abamectin decreased significantly with

242

depth in the soil columns. Apparently, EC was more easily to be maintained at a depth

243

of 0-5 cm (64.29% of added abamectin), whereas that of MCs was the most difficult

244

to maintain in the upper portion of the columns. In summary, all belong to the grade

245

of hard-to-leach, although the leaching of abamectin with different formulations

246

differs.

247

Mobility of abamectin with different formulations in the soil thin layer

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As illustrated in Figure 4a, all treatments of abamectin with different formulations

249

reached distances of 15-18 cm, even though significant differences were observed in

250

terms of the mobility of abamectin. Most abamectin was maintained at a distance of

251

0-3 cm for the EC and SC groups (approximately 62% and 74%, respectively),

252

whereas that of MCs was uniformly distributed. The same trend was observed for the 12


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mass fraction of abamectin, which decreased significantly with distance from the

254

original point. The relative shift (Rf) of abamectin with different formulations were

255

depicted in Figure 4b. Abamectin EC and SC belong to the grade of hard-to-move,

256

whereas that of MCs belongs to the medium mobility grade.

257 258

Discussion and conclusions

259

Sensitivity of M. incognita collected from different regions to abamectin

260

Although long-term frequent contact would decrease the sensitivity of nematodes to

261

pesticides, resistance problems have not been extensively reported 37, 38. In the current

262

study, toxicity of abamectin to J2 of M. incognita collected from five different regions

263

exhibited insignificant differences (considering LC50 values) regardless of slight

264

sensitivity variations. We speculated that the sensibility of M. incognita to abamectin

265

and the approaches of applying pesticides may be two key factors leading to the

266

inconsistent efficacy of abamectin in different experimental fields. But the

267

insignificant differences demonstrated that the sensitivity of M. incognita to

268

abamectin was not a possible factor. To date, available nematicides registered for the

269

management of RKN were still insufficient. Although abamectin and fosthiazate were

270

highly efficient nematicides against M. Spp., their frequent use would exert immense

271

selective pressure on RKN. Therefore, seeking for highly efficient nematicides with

272

different modes of action was still imperative.

273

Formulation type influences the efficacy of abamectin on RKN of tomatoes

274

Southern root-knot nematodes mainly distribute at a depth of 0-20 cm, especially in 13



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the 0-10 cm layer of soil during the growing season for vegetables under protective

276

cultivation

277

where targeted nematodes primarily gather would greatly influence their efficacies. As

278

demonstrated in Table 2, EC groups had the highest adsorption ratios, which

279

dramatically decreased soil mobility. In contrast, MCs were thought to be more likely

280

to leach or move in the soil. We speculated that the adsorbable nature of abamectin

281

would be modified after encapsulated with polymeric wall materials and thus resulted

282

in higher leaching and mobility of MCs in the soil. As depicted in Figure 3, more

283

active ingredient of abamectin in MCs groups was available to contact with M.

284

incognita in the depth of 15-20 cm via relatively uniform distribution of abamectin.

285

Thus, abamectin in MC groups has a greater chance of providing sufficient protection

286

over the wide 0-20 cm depth range in the soil. Therefore, we conclude that

287

formulation types can influence the efficacy of abamectin on the RKN of tomatoes,

288

and MCs showed certain advantages.

289

MCs exhibited higher safety to tomato plants compared with EC

290

In this study, the root length of EC groups dropped dramatically with the dosage of

291

abamectin, whereas that of MCs groups increased gradually regardless of the

292

application approach adopted (Figure 2a and b). SCs also exhibited higher safety to

293

tomato plants in terms of root length. Moreover, plant height, fresh weight of root,

294

and fresh weight of stems and leaves of MCs at 5 and 10 mg per plant were also

295

superior over EC groups. Figure 3 and 4 demonstrated that MCs were more likely to

296

leach and move in the soil, and thus the active ingredient of MCs groups was better

39

. We previously stated that whether pesticides could retain the position

14


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distributed and the regional concentrations of MCs were much lower than EC groups,

298

which in return led to higher safety to tomato plants. We also found that using EC at a

299

dosage of 10 mg per plant can cause obvious phytotoxicity to tomato plants under

300

field conditions (root-irrigation), unlike MCs treatment (Figure 5). Necrosis and

301

constriction were observed on the epidermis of the basal part of the stem, consistent

302

with our pot experiments and previously reported publications 28. But no phytotoxicity

303

symptoms were observed for all treatments in terms of blending-of-soil method. As

304

was shown in leaching and mobility experiments, MCs can be better distributed in the

305

soil than EC and SC and thus cause little phytotoxicity risk. This would be the main

306

factor that influences its phytotoxicity to tomato.

307

Necessity for precise pesticide delivery technology

308

Ideal pesticide application technology is capable of delivering chemicals to their

309

targets. We therefore would achieve enhanced efficacy against pests, environmental

310

pollution would be eased, and side effects to higher-order organisms and non-target

311

organisms are lowered. Given the characteristics of occurrence and damage of RKN,

312

various pesticide application approaches can be employed, including blending-of-soil,

313

broadcasting granule, root-irrigation, hole-application, furrow application, spraying

314

on the soil surface and drip irrigation. Blending-of-soil was capable of generating a

315

uniform distribution of active ingredient, whereas we could barely obtain similar

316

performance under root-irrigation conditions

317

treatment showed better efficacy than the root-irrigation treatment (Figure 1).

318

However, the blending-of-soil is a time-consuming method. Broadcasting granules are

29

. Therefore, the blending-of-soil

15



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easy to handle, but the pesticide is difficult to uniformly distribute. Thus, it cannot

320

provide sufficient protection for the entire plant

321

pesticides could be obtained by modifying the formulation (e.g., MCs), precise

322

pesticide application technology must still be developed.

323

Acknowledgements

324

This work was supported by grants from the National Key Research Development

325

Program of China (2017YFD0200307; 2016YFD0201600) and the National Natural

326

Science Foundation of China (31772203).

327

Supporting information

328

The fresh weights of tomato roots, stems and leaves under different application

329

approaches in pot experiments are shown as Figure S1. The design of pot experiments

330

is listed in Table S1. Detailed methods for blending-of-soil and root-irrigation are

331

elaborated in the Supporting Information. Detailed operating parameters for

332

UPLC-MS/MS system are described in the Supporting Information. Accuracy of

333

using PSA solid phase extraction (SPE) cartridge to purify the mixture is also

334

described in the Supporting Information.

335

Declaration of interest statement

336

The authors declare no competing financial interest.

28

. Although better distribution of

337 338

References

339

1.

340

Verdejo-Lucas, S. Damage functions and thermal requirements of Meloidogyne

López-Gómez, M.; Gine, A.; Vela, M. D.; Ornat, C.; Sorribas, F. J.; Talavera, M.;

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javanica and Meloidogyne incognita on watermelon. Ann. Appl. Biol. 2014, 165,

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466-473.

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2.

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Meloidogyne project-its goals and accomplishments. Annu. Rev. Phytopathol. 1983,

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464

Plant Prot. 2011, 37, 105-109.

to

commonly-used

nematicides

in

Shandong

Province.

Acta

465

22


Page 23 of 31


466

Table 1 Toxicity of abamectin to M. incognita collected from different regions Sampling

Exposure

Toxicity regression

site

duration (h)

equation (Y =)

Dongdawu

24

3.68 + 1.95x

48 Caosi

Kangzhuang

Liuyi farm

Lujiazhuang

R2

LC50 (mg/L)

LC90 (mg/L)

95% confidence limit

95% confidence limit

0.98

4.76 (3.47-6.53)

21.68 (14.42-32.59)

2.99 + 3.00x

0.89

4.65 (2.06-10.50)

12.46 (5.07-30.60)

24

4.52 + 0.86x

0.96

3.59 (1.87-6.90)

109.66 (26.22-458.55)

48

4.63+0.89x

0.96

2.63 (1.39-4.97)

71.88 (19.07-270.97)

24

469 + 1.13x

0.98

1.89 (0.81-4.40)

25.67 (7.89-83.51)

48

4.71 + 1.17x

0.98

1.77 (0.77-4.10)

22.30 (7.05-70.56)

24

4.46 + 0.22x

0.96

2.26 (1.11-4.57)

15.83 (5.11-49.02)

48

4.47 + 1.59x

0.97

2.16 (1.18-3.96)

13.87 (5.37-35.84)

24

4.35 + 2.82x

0.97

1.70 (0.92-3.15)

4.85 (2.94-8.01)

48

4.39 + 2.80x

0.97

1.65 (0.90-3.02)

4.73 (2.89-7.73)

23



467

Page 24 of 31

Table 2 Adsorption of abamectin with different formulations in the soil Initial concentration

Equilibrium

Adsorbing capacity

Adsorption ratio

(mg/L)

concentration (mg/L)

(mg/kg)

(%)

Abamectin

0.5

0.034±0.0007

4.577±0.0278

93.02±0.1719

EC

1

0.067±0.0017

9.065±0.0166

93.15±0.1601

5

0.226±0.0385

47.51±0.3790

95.47±0.7738

10

0.603±0.0403

91.66±0.5960

93.83±0.4246

Abamectin

0.5

0.070±0.0008

4.137±0.0224

85.62±0.1304

SC

1

0.122±0.0021

8.427±0.1111

87.34±0.3354

5

0.567±0.0086

44.12±0.0916

88.62±0.1714

10

1.231±0.0153

85.34±0.2335

87.40±0.1343

Abamectin

0.5

0.072±0.0009

4.095±0.0326

85.11±0.2549

MCs

1

0.140±0.0021

8.212±0.0150

85.45±0.1685

5

0.749±0.0146

42.29±0.1514

84.96±0.2943

10

1.514±0.0125

82.24±0.3586

84.45±0.1654

Nematicide

468

Note: Data were displayed as means ± SD (n=3).

24


Page 25 of 31


469

Figure captions

470

Figure 1 Control efficacy of abamectin on RKN of tomato under different application

471

approaches in pot experiments. (a) blending of soil and (b) root-irrigation. Data were

472

displayed as means ± SE. Control efficacy was arcsine transformed, and then

473

subjected to analysis of variance. Values of same application approach with different

474

lower case letters are significantly different at P< 0.05 level by LSD test.

475

Figure 2 Growth indices of tomatoes under different application approaches in pot

476

experiments: (a and c) blending-of-soil and (b and d) root-irrigation. Data were

477

displayed as means ± SE. Values of same application approach with different lower

478

case letters are significantly different at P< 0.05 level by LSD test.

479

Figure 3 Distribution of abamectin with different formulations in soil columns. Data

480

were displayed as means ± SE. Mass fraction of abamectin was arcsine transformed,

481

and then subjected to analysis of variance. Values with different lower case letters are

482

significantly different at P< 0.05 level by LSD test.

483

Figure 4 (a) Mobility of abamectin with different formulations in soil thin layer. (b)

484

Relative shift values of abamectin in soil thin layer. Data were displayed as means ±

485

SE. Mass fraction of abamectin was arcsine transformed, and then subjected to

486

analysis of variance while that of relative shift values were directed subjected to

487

analysis of variance. Values with different lower case letters are significantly different

488

at P< 0.05 level by LSD test.

489

Figure 5 Images of phytotoxicity of tomato after root-irrigation with abamectin

490

emulsifiable concentrate at dosage of 10 mg per plant. 25



Figure 1 Control efficacy of abamectin on RKN of tomato under different application approaches in pot experiments. (a) blending of soil and (b) root-irrigation. Data were displayed as means ± SE. Control efficacy was arcsine transformed, and then subjected to analysis of variance. Values of same application approach with different lower case letters are significantly different at P< 0.05 level by LSD test. 74x106mm (300 x 300 DPI)


Page 26 of 31

Page 27 of 31


Figure 2 Growth indices of tomatoes under different application approaches in pot experiments: (a and c) blending-of-soil and (b and d) root-irrigation. Data were displayed as means ± SE. Values of same application approach with different lower case letters are significantly different at P< 0.05 level by LSD test. 149x115mm (300 x 300 DPI)



Figure 3 Distribution of abamectin with different formulations in soil columns. Data were displayed as means ± SE. Mass fraction of abamectin was arcsine transformed, and then subjected to analysis of variance. Values with different lower case letters are significantly different at P< 0.05 level by LSD test. 71x69mm (300 x 300 DPI)


Page 28 of 31

Page 29 of 31


Figure 4 (a) Mobility of abamectin with different formulations in soil thin layer. (b) Relative shift values of abamectin in soil thin layer. Data were displayed as means ± SE. Mass fraction of abamectin was arcsine transformed, and then subjected to analysis of variance while that of relative shift values were directed subjected to analysis of variance. Values with different lower case letters are significantly different at P< 0.05 level by LSD test. 109x160mm (300 x 300 DPI)



Figure 5 Images of phytotoxicity of tomato after root-irrigation with abamectin emulsifiable concentrate at dosage of 10 mg per plant. 165x140mm (300 x 300 DPI)


Page 30 of 31

Page 31 of 31


ToC graph 49x29mm (300 x 300 DPI)


Modifying the formulation of abamectin to promote its efficacy on

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