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Article

Spatiotemporal Dynamics of Trunk-Injected Pesticide Residue for Management of Pine Wilt Disease in Pinus koraiensis

by
Min-Jung Kim
1,†,
Junheon Kim
1,*,†,
Nam Sik Yoo
1 and
Jong-Kook Jung
2
1
Forest Insect Pests and Diseases Division, National Institute of Forest Research, Seoul 02455, Republic of Korea
2
Department of Forest Environment Protection, Kangwon National University, Chuncheon 24341, Republic of Korea
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Forests 2024, 15(11), 1996; https://doi.org/10.3390/f15111996
Submission received: 16 October 2024 / Revised: 7 November 2024 / Accepted: 11 November 2024 / Published: 12 November 2024
(This article belongs to the Section Forest Ecology and Management)
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Abstract

:
This study focused on the persistence, distribution, and efficacy of trunk-injected pesticides in Pinus koraiensis (Korean pine) with regard to controlling pinewood nematodes (PWNs, Bursaphelenchus xylophilus), the causative agent of pine wilt disease (PWD). In this study, we compared pesticide residues in the needles and branches of Korean pine, revealing significant declines in pesticide residues over time after treatments were applied. Notably, abamectin residues decreased from 0.2325 mg/kg to 0.0901 mg/kg in branches over a period of 18 months. In contrast, emamectin benzoate showed a variation in residue decline depending on the formulation, with the residue level in branches decreasing from 0.1220 mg/kg to 0.0328 mg/kg over the same period. From a spatial perspective, the results revealed minimal differences in pesticide residue at varying tree heights, although a decrease in upper canopy residue was observed in some cases. The nematicidal efficacy test demonstrated that none of the treated trees developed PWN symptoms. Overall, the findings suggest that the trunk-injected pesticides abamectin and emamectin benzoate can persist for two years, with the residue levels being sufficient to prevent PWN propagation, even when the levels are below critical inhibition concentrations.

Graphical Abstract

1. Introduction

The pinewood nematode (PWN; Bursaphelenchus xylophilus) is responsible for pine wilt disease (PWD), a plant disease that endangers pine forest ecosystems and poses international quarantine issues [1]. The PWN is native to North America and is widely distributed across that continent and in Asia and Europe [1]. PWNs spread primarily by insect vectors of the genus Monochamus, including M. alternatus, M. saltuarius, and M. galloprovincialis [1,2,3], making infestations difficult to control due to the mobility of the vectors [4,5,6].
Since the first introduction of PWNs in Korea in 1988 [7], PWD has spread among various pine species, including red pine (Pinus densiflora), black pine (P. thunbergii), and Korean pine (P. koraiensis) [1,2,8]. In China, P. koraiensis has also been reported to be susceptible to PWNs and to be infected by PWNs [9].
Foliar spraying methods may have adverse impacts, including environmental pollution, human exposure, and the unintended ingestion of chemicals by nontarget organisms. In contrast, tree trunk injection, in which pesticides are directly injected into target trees, is expected to reduce these risks, especially that of human exposure [10]. For the management of PWD, trunk injection of pesticides, particularly avermectins, has been widely studied [11,12,13,14,15]. As the primary strategy for preventing the spread of PWD in Korea, trunk injection of pesticides has been performed. Many chemical agents, such as abamectin and emamectin benzoate, and their combinations with acetamiprid, dinotefuran, or sulfoxaflor are commonly used [16,17,18].
Trunk injection involves administering a chemical agent directly into the trunks of trees, where its movement within the tree relies on water being transported through the xylem [13,19,20]. The spatiotemporal uniformity of the distribution of the agent within tree tissues is a critical factor that influences the effectiveness of trunk-injected pesticides in trees [12]. In terms of the efficacy of trunk injection against PWNs, the position, size, and number of pesticide injection holes have been studied [21,22,23]. Studies have reported pesticide efficacy, persistence, distribution, and residue on P. densiflora or P. thunbergii branches after trunk injection [14,21,22,24]; however, there are no similar reports on P. koraiensis needles and branches. Therefore, we investigated the temporal and spatial distribution, efficacy, persistence, and residues of pesticides in P. koraiensis needles and branches. These results can serve as a basis for understanding the efficacy of trunk injection for controlling PWD.

2. Materials and Methods

2.1. Study Area

The study was conducted in Yangpyeong, Gyeonggi, the central region of the Republic of Korea. Yangpyeong is a key region for pine nut production, which has led to extensive planting of P. koraiensis throughout the area. Pesticide residue analysis in P. koraiensis and pesticide efficacy testing were conducted at two separate locations: the pesticide residue analysis plot (PRA plot: 37°36′44″ N 127°38′04″ E) and the pesticide efficacy test plot (PET plot, 37°37’5″ N 127°38′46″ E). The PRA plot was located along a forested road, where a lift car could be used to sample the needles and branches. PWD had not occurred in the study area, and the trees had never been trunk-injected with pesticides. The control plot for the pesticide efficacy test (PET Ctrl B, 37°26′16″ N 127°41′31″ E) was approximately 25 km away from the PET plot, where PWD occurred in 2021 and nematode-infected trees were subsequently removed (Figure S1).

2.2. Pesticides, Chemicals, and Reagents

The pesticides used for trunk injection, abamectin dispersible concentrate (DC) (1.8%; P1, P2), emamectin benzoate emulsifiable concentrate (EC) (2.15%; P3, P4, P5, P6, P7), abamectin (1.6%)–acetamiprid (7%) microemulsion (ME) (8.6%; P8), abamectin (1.8%)–sulfoxaflor (4.2%) DC (6%; P9), and acetamiprid (8%)–emamectin benzoate (2%) DC (10%; P10), were purchased through a vendor. The details of the pesticides are listed in Table 1. The pesticide standards were obtained from AccuStandard, Inc. (New Haven, CT, USA) and had a purity of >95%. Individual stock solutions (1000 μg/mL) of each pesticide standard were prepared in acetonitrile (MeCN) and acetone. Quick, easy, cheap, effective, rugged and safe (QuEChERS) kits were purchased from BEKOlut (Hauptstuhl, Germany). The extraction kits contained 4 g of anhydrous MgSO4, 1 g of NaCl, 1 g of sodium citrate tribasic dihydrate, and 0.5 g of sodium citrate dibasic sesquihydrate. Dispersive SPE kits, consisting of 150 mg of primary secondary amine (PSA; average particle size 40 µm) and 900 mg of MgSO4, were used to clean 5 mL of sample extract. HPLC-grade acetonitrile (99.9%), methanol (99.9%), and water were purchased from J.T. Baker (Philipsburg, NJ, USA) or Fisher Scientific (Hampton, VA, USA). The buffer solution used to dilute the samples was 100 mM ammonium formate in water (pH 4–4.5), which was used for liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis.

2.3. Trunk Injection and Sample Collection

The experimental sites were divided into 11 sectors, with different pesticides randomly assigned to each sector in both plots (Supplementary Data, Figure S1). In the PRA plot, five trees were assigned to each sector. As a control in the PRA plot (Ctrl A), no pesticide was injected into one sector. In the PET plot, approximately 45 trees were distributed per sector, with 35 trees randomly selected for trunk injection.
Pesticides chosen by the Pesticide Review Committee of the Korea Forest Service were injected. Among the chosen pesticides, emamectin benzoate, in particular, is one of the pesticides most commonly used by the top five companies in Korea. Trunk injection was performed once in December 2021 according to the method outlined in the KFS manual [16]. The injection amount was chosen in accordance with the manufacturer’s instructions (1 mL/cm diameter at breast height (DBH)). For trunk injection, holes (10 mm in diameter, 4–6 mm in depth) were drilled into the P. koraiensis Korean pine tree at approximately 50 cm above the ground and angled downward at 45° using an engine-powered machine (TB-43, Mitsubishi Heavy Industries, Tokyo, Japan) with a drilling adapter and a wood drill bit (Φ 10 mm, length 170 mm). The holes were distributed evenly around the tree. For residue analysis, each pesticide was applied to 5 trees, and for the efficacy test, pesticides were applied to 30 trees for each pesticide. After pesticide injection in December 2021, the needles and branches of P. koraiensis were collected from the upper, middle, and lower canopy in May and October of 2022, and distal branches were cut at depths of approximately 30 cm in three different directions at each position via a lift car.

2.4. Residue Sample Preparation

Sample extraction was performed according to the Korea Food Code pesticide analysis guidelines MFDS, [25]. Needles were separated from the collected branches and both the needles and branches were ground separately via a blender. The samples were prepared via a QuEChERS kit. A 5 g sample was placed into a 50 mL centrifuge tube and 5 mL of water was added to facilitate extraction. After 1 h, 10 mL of acetonitrile was added, and the mixture was vortexed for 1 min. The Bekolut QuEChERS Extraction Kit (containing 4 g anhydrous magnesium sulfate, 1 g sodium chloride, 1 g sodium citrate tribasic dihydrate, and 0.5 g sodium citrate dibasic sesquihydrate) was subsequently added, and the mixture was shaken for 2 min to complete the extraction process, followed by centrifugation. The supernatant was filtered through an NY syringe filter (with a thickness of 0.22 μm and a diameter of 17 mm), and a certain amount of buffer solution (prepared by adjusting the water containing 100 mM ammonium formate with formic acid solution to pH 4–4.5) was added.

2.5. LC-MS/MS Analysis

Analysis of needles and branches of P. koraiensis was performed at Jeonju University. LC-MS/MS analysis was conducted via a Shimadzu LC-8040 instrument (a liquid chromatograph with a triple quadrupole mass detector; Shimadzu, Kyoto, Japan), and the separation of pesticides was achieved via a Pursuit XRS Ultra C18 column (100 mm × 2.0 mm, 2.8 μm particle size; Agilent Technologies, Santa Clara, CA, USA). Deionized water with 5 mM ammonium acetate and 0.1% formic acid (mobile phase A) and acetonitrile with 5 mM ammonium acetate and 0.1% formic acid (mobile phase B) were used for the gradient program: 10% B for 1 min and a linear increase to 98% B over 15 min. The column was reconditioned for 4 min at 10% B at the end of the program. The column temperature was kept at 40 °C and the injection volume was 20 μL, with a constant flow rate of 0.3 mL/min. The ESI source was used in positive and negative mode, the nebulizing gas flow rate was 3 L/min, the drying gas flow rate was 15 L/min, the DL temperature was 250 °C, and the heat block temperature was set at 400 °C. The MS data were obtained in MRM mode.

2.6. Method Validation

To validate the analytical method, precision and accuracy were evaluated. Precision was assessed by the percent relative standard deviation (%RSD) of repeated measurements, whereas accuracy was evaluated by repeating recovery experiments at specific concentrations according to the Korea Food Code pesticide analysis guidelines [25,26]. The recovery experiments were conducted in triplicate by spiking untreated pine needles or branches at concentrations of 10, 30, and 50 μg/kg. The %RSD of the triplicate recovery experiments for precision ranged from 0.4% to 6.9% (Table 2), and the recovery rates ranged from 83% to 110% (Table 2), meeting the criteria for quantitative analysis [27].

2.7. Nematicidal Efficacy and Persistence Test

The nematicidal effect was confirmed in the second year after trunk injection (2023) because all the tested pesticides were registered with guaranteed nematicidal effects for one year. To determine whether the effectiveness of trunk-injected pesticides lasts for two years, we inoculated PWNs into pesticide-treated and untreated P. koraiensis trees in May 2023 (second year). P1, P3, P8, P9, and P10 were tested. Trees in P1 and P3 were chosen randomly from among the abamectin DC (1.8%) and emamectin benzoate (2.15%) EC treatments. Thirty trunk-injected trees were chosen at random. A hole was drilled with a drill bit (diameter of 8 mm) via an electric drill (FJ Tech, Gimpo, Republic of Korea) at 1.5 m above the ground, and each tree was inoculated with approximately 20,000 pine wood nematodes (PWNs, Bursaphelenchus xylophilus), which were reared in the laboratory of the Pine Wood Nematode, National Institute of Forest Science, Seoul, Republic of Korea. The cumulative mortality of the Korean pine trees was assessed in October and November 2023 and June 2024. To assess PWN mortality, first, the appearance of the inoculated trees was observed. When all the needles turned brown, we considered them to be infected with PWD; if no change in appearance was found, they were considered to be infection-free. Second, approximately 40 g of sawdust was collected from each nematode-treated tree via an electronic drill (FJ Tech) to confirm the presence of PWNs. The nematodes were extracted from the sawdust via the Baermann funnel method and counted under a microscope.

2.8. Statistical Analysis

The pesticide residue levels exhibited a right-skewed distribution across all the treatments; therefore, the data were square root-transformed to approximate normality and stabilize variance. Initially, the effects of collection height (upper, middle, and lower) on pesticide residue were analyzed via ANOVA without considering sampling time or tree parts (branches and needles). For 8 out of the 13 examined active ingredients from 10 pesticides, no significant differences in residue levels were found according to collection height at a 5% error rate. Five cases presented a statistically significant effect related to height (p < 0.05). However, because the primary objective of the study was to evaluate the effects of time and tree part on pesticide residue dynamics, the effect of height was not considered in subsequent analyses.
To analyze residue dynamics, a linear mixed-effects model (LME) was employed, with time after trunk injection and tree part as fixed effects and individual trees treated as a random effect to account for variability between trees. The time variable was treated as categorical rather than continuous due to irregular time intervals, and there was no strong basis to assume a linear relationship between time and residue levels. The model was fitted via the lme4 package in R 4.2.2, and the significance of fixed effects (time and tree parts) was determined via Type II Wald chi-squared tests.

3. Results

The temporal dynamics in pesticide residues in the needles and branches of trees are represented in Figure 1 as the square root-transformed values. The temporal and spatial changes in pesticide residues in needles and branches are reported as untransformed values in the Supplementary Data (Table S1).

3.1. Temporal Changes in Pesticide Residue

The residue levels of all the active ingredients were significantly affected by time after trunk injection (Table 3), but the residue dynamics varied among the pesticides. Pesticides other than emamectin benzoate EC (2.15%) presented a significant decrease in residue levels over time, as indicated by negative regression coefficients (Table 3, Figure 1, Table S1). In contrast, emamectin benzoate EC (2.15%) exhibited no clear decrease in residue with time over the two-year monitoring period. Specifically, emamectin benzoate EC (2.15%) initially showed an increase in residue levels following injection, but when the final measurement was obtained at the two-year mark, the residue levels had decreased. However, a different pattern was observed for the mixtures of emamectin benzoate (2%) and acetamiprid (8%) DC, in which residue levels significantly decreased over time. No pesticide residues were detected in the control plot.
The initial amounts of residues of abamectin DC (1.8%) in needles were 0.208 mg/kg (P1) and 0.4789 mg/kg (P2) in May 2022, which declined to 0.0186 mg/kg (P1) and 0.0374 mg/kg (P2) by October 2023 (Table S1), and those in branches were 0.0227 mg/kg (P1) and 0.0489 mg/kg (P2), which declined to 0.0056 mg/kg (P1) and 0.0401 mg/kg (P2). The residual ratios of the residue at the final date (October 2023) to the initial date (May 2022) in the needles were 8.93% (P1) and 7.81% (P2), and branches were 24.67% (P1) and 82.00% (P2).
For emamectin benzoate EC (2.15%), the residues in needles and branches varied depending on the product. In May 2022, the residues in needles ranged from 0.0158 mg/kg (P7) to 0.1125 mg/kg (P3), which decreased to between 0.0121 mg/kg (P6) and 0.0337 mg/kg (P3) by October 2023. The range of initial residue in branches was 0.0090 mg/kg (P7)–0.0327 (P3) mg/kg, and the range of final residue was 0.0108 mg/kg (P6)–0.0248 mg/kg (P3). The ratios of residue amounts in needles and branches from October 2023 to May 2022 ranged from 20.26% to 93.67% and from 45.86% to 152.22%, respectively.
Table 3. Results of the effects of time (after trunk injection) and tree part (needles and branches) on pesticide residue levels.
Table 3. Results of the effects of time (after trunk injection) and tree part (needles and branches) on pesticide residue levels.
CodePesticideVariabledfχ2-Valuep-Value
P1AbamectinTime353.362<0.0001
Part197.989<0.0001
P2AbamectinTime361.533<0.0001
Part167.07<0.0001
P3Emamectin benzoateTime37.93510.0474
Part13.93180.0474
P4Emamectin benzoateTime313.29230.0040
Part17.81250.0052
P5Emamectin benzoateTime319.43750.0002
Part16.20960.0127
P6Emamectin benzoateTime311.1340.0110
Part112.1020.0005
P7Emamectin benzoateTime38.40060.0384
Part14.19680.0405
P8AbamectinTime393.287<0.0001
Part176.292<0.0001
AcetamipridTime337.076<0.0001
Part1225.846<0.0001
P9AbamectinTime349.428<0.0001
Part123.648<0.0001
SulfoxaflorTime354.03<0.0001
Part152.094<0.0001
P10Emamectin benzoateTime378.577<0.0001
Part137.595<0.0001
AcetamipridTime340.715<0.0001
Part1234.243<0.0001
The square root-transformed residue values were analyzed via a linear mixed-effects model (LME), with the time after injection and tree part as fixed effects and individual trees treated as random effects to account for variability between trees. The significance of the fixed effects was evaluated via Type II Wald chi-squared tests, in which the full model was compared to a null model that incorporated only the random effects of individual trees.
The abamectin residues in abamectin (1.6%)–acetamiprid (7%) ME (P8) were measured, with 1.2675 mg/kg identified in needles and 0.1413 mg/kg identified in branches in May 2022 (Table S1). These values were higher than those for abamectin DC (1.8%) (P1 and P2), which had residues of 0.4789 mg/kg in needles and 0.0489 mg/kg in branches. By October 2023, the residues in needles and branches had decreased to 0.0626 mg/kg and 0.0498 mg/kg, respectively. The acetamiprid residues in P8 were 6.3579 mg/kg in needles and 0.6951 mg/kg in branches in May 2022 and decreased to 1.8958 mg/kg in needles and 0.0098 mg/kg in branches by October 2023. The ratios of the amount of residue in branches in October 2023 and May 2022 for abamectin and acetamiprid were 35.24% and 1.41%, respectively.
The abamectin residues in abamectin (1.8%)–sulfoxaflor (4.2%) DC (P9) were 1.4967 mg/kg in needles and 0.2325 mg/kg in branches in May 2022 (Table S1). The residue dynamics for abamectin in P9 were similar to those in P8. The sulfoxaflor residues in P9 were 5.8211 mg/kg in needles and 0.1328 mg/kg in branches in May 2022, but sulfoxaflor was undetectable in October 2023. The ratio of the amount of residue in branches in October 2023 and in May 2022 for abamectin was 38.75%, whereas sulfoxaflor was not detected in October 2023.
The residues of emamectin benzoate in acetamiprid (8%)–emamectin benzoate (2%) DC (P10) amounted to 0.4581 mg/kg and 0.1201 mg/kg in needles and branches, respectively, in May 2022 and decreased to 0.0386 mg/kg and 0.0328 mg/kg by October 2023 (Table S1). The acetamiprid residues in P10 were measured, with 7.8776 mg/kg identified in needles and 0.5705 mg/kg in branches in May 2022; they decreased to 1.7292 mg/kg in needles and 0.0181 mg/kg in branches by October 2023. The ratios of the amount of residue in branches in October 2023 and in May 2022 for emamectin benzoate and acetamiprid were 27.31% and 3.17%, respectively.

3.2. Pesticide Residue in Needles and Branches

The residues of all trunk-injected pesticides in the needles were significantly greater than those in the branches throughout the study period (Table 3, Figure 1). This trend persisted over time, with the exceptions of P5 in May 2023 and P2 and P3 in October 2023 (Table S1, Figure 1). The ratio of residue levels in the needles to those in the branches varied considerably, regardless of pesticide type. For the nematicides, the ratio of abamectin residues ranged from 0.93 to 12.00 (mean: 5.53), whereas for emamectin benzoate, it ranged from 0.83 to 16.43 (mean: 2.59). The ratios for the insecticides were even broader. The content of acetamiprid ranged from 5.39 to 312.32 (mean: 110.94), and that of sulfoxaflor ranged from 43.83 to 259.68 (mean: 129.90).

3.3. Vertical Distribution of Pesticide Residues at Different Tree Positions (Upper, Middle, and Lower Canopy)

Most of the pesticides examined showed no significant differences in the within-tree distribution of pesticide residues depending on sampling height, except in P5, P6, P7, and P9 (Table 4 and Table S1). For pesticides that exhibited significant differences, the residue levels generally decreased with height, resulting in lower residue levels in the upper canopy than in the lower canopy in many cases.

3.4. Nematicidal Efficacy Test

In trunk-injected trees (P9 and P10), PWD symptoms were observed (one of each); however, no PWNs were detected via the Baermann funnel method. Therefore, we concluded that the wilt observed was not a result of PWN infection. No PWD symptoms were observed in other trunk-injected trees (P1–P8). In the control plot (Ctrl B), all 24 trees presented PWD symptoms in October 2023 (6 trees were not investigated because they were removed by the city and disposed of prior to the investigation), and PWNs were found in all trees showing PWD symptoms. The severity of PWD symptoms increased from November 2023 to June 2024. In November 2023, 12 (50%) PWN-infected trees died, and in June 2024, 17 (70.8%) died (Table S2).

4. Discussion

The temporal and spatial distribution, efficacy, persistence, and residues of pesticides in P. koraiensis needles and branches were investigated. The pesticide residues persisted for two years after trunk injection in this experiment. Previous studies reported that emamectin benzoate persisted for three years after trunk injection in P. densiflora. The residue levels of emamectin benzoate ranged from 0.0090 mg/kg to 0.1201 mg/kg in P. koraiensis branches five months after injection, whereas in P. densiflora branches, the residue levels ranged from 0.0052 mg/kg to 1.7356 mg/kg four months after injection [21,22]. The residues of abamectin and emamectin benzoate in P. densiflora branches were 0.039–0.191 mg/kg and 0.011–0.222 mg/kg, respectively, 585 days (approximately 20 months) after trunk injection [24]. In P. koraiensis branches, abamectin and emamectin benzoate residues were present at 0.0056–0.0502 mg/kg and 0.0072–0.0328 mg/kg, respectively, 22 months after trunk injection. The residues in P. koraiensis were lower than those in P. densiflora, possibly due to the large volume of P. koraiensis. In our experiments, P. koraiensis had a diameter nearly twice that of P. densiflora as determined by Lee et al. and Kwon et al. [21,22,24]. The residue dynamics differed between broad-leaved trees and conifers. In pecan leaves, the emamectin benzoate residue at 100 days after injection decreased to 7.51%–53.59% (mean: 21.10%) of the residue at 10 [28]. In contrast, in P. koraiensis, the residue levels at 10 months after injection increased by 80.8%–343.1% (mean: 158.1%) of 5 months. This difference may be attributed to the variation in the vascular system of broad-leaved trees and conifers [29]. While height was not a primary focus in our study, we observed a decrease in pesticide residue with increasing tree height in P. koraiensis in some cases, although more than half of the pesticide residue levels did not significantly differ. Takai et al. (2004) reported that emamectin benzoate residues decreased with height in 6-year-old P. thunbergii trees [13]. Kwon et al. [21] reported that emamectin benzoate residues did not significantly differ by height in the first year, although residues were greater in lower parts, and the difference became significant by three years after injection. When pesticides are injected into tree trunks, pesticide movement within a tree is driven by water transport through the xylem [13,19,20]. Resin canals in the xylem could reduce the uptake of injected compounds [30,31]. The water potential in the upper canopy is typically lower than that in the lower canopy, and as the pesticide moves upward, it passes more resin canals. Therefore, a difference in water transport and pesticide uptake could result in spatial variation in residue distribution.
Differences in residue between needles and branches were reported for the first time in our experiments. The residues in needles were much greater than those in branches. This could have resulted from water transport differences, as the water potential of needles is greater than that of branches [32]. The needles of P. koraiensis fall to the ground the year after they develop. Therefore, pesticide injected into a tree in December 2021 remained in the needles and then accumulated on the ground when the needles dropped in fall 2022, with residues ranging from 0.116 to 0.5418 mg/kg for abamectin, 0.0172 to 0.3860 mg/kg for emamectin benzoate, 1.2984 mg/kg for sulfoxaflor, and 4.8128 to 7.2105 mg/kg for acetamiprid. It is likely that the pesticide present in fallen needles on the soil leached into the soil, leading to pesticide residue in the soil and potentially having negative impacts on nontarget insects. These negative effects have not been investigated, so future research is necessary to determine what the effects might be.
In the second year, all trunk-injected trees survived, indicating that the nematicidal efficacy persisted. The persistence of pesticide trunk injection efficacy has been reported for abamectin and emamectin benzoate [11,13,15]. The residues in branches in May 2023 (second year) were 0.0115–0.1120 mg/kg for abamectin and 0.0120–0.0508 mg for emamectin benzoate. Some pesticide residues were below the 95% inhibition concentration (IC95) value (0.031 mg/kg) for PWN control, as suggested by Takai et al. (2003, 2004), for P. thunbergii [13,33]. Although the residue levels were below the suggested IC95 values, no trunk-injected trees presented symptoms of PWN infection. Given that the susceptibility of P. koraiensis and P. thunbergii is similar [34], it is surprising that P. koraiensis showed no symptoms of PWD despite the low residue levels. The nematicidal effect of trunk-injected pesticides persisted for two years, and residue levels of 0.0115 mg/kg for abamectin and 0.0120 mg/kg for emamectin benzoate in spring of the second year were sufficient to prevent PWN propagation.

5. Conclusions

Trunk-injected pesticides, specifically abamectin and emamectin benzoate, show sustained persistence in P. koraiensis over two years, maintaining sufficient residue levels to prevent the spread of pinewood nematodes (PWNs), which cause pine wilt disease (PWD). Only minor differences in pesticide residue distribution along the height of the trees was observed, with some reduction in the upper canopy. The nematicidal efficacy test further confirmed the effectiveness of the treatments, as no treated trees exhibited PWN symptoms, highlighting the potential of these trunk-injected pesticides as a viable, lasting option for PWN management.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/f15111996/s1, Figure S1: The location of pesticide residue test and nematicidal efficacy test. Table S1: The trunk-injected pesticide residues. Table S2: Severity of pine disease symptom on pesticide-untreated Pinus koraiensis (control).

Author Contributions

Conception: J.K.; methodology: J.-K.J. and N.S.Y.; Investigation: J.K. and J.-K.J.; Statistical analysis: M.-J.K., J.-K.J. and J.K.; Writing—original draft preparation: J.K. and M.-J.K.; Writing–review and editing: J.K., M.-J.K., N.S.Y. and J.-K.J.; Funding acquisition: J.K. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Korea Forest Service and National Institute of Forest Science, grant numbers FB0100-2022-03 and FE0703-2024-01.

Data Availability Statement

Data are available from the corresponding author upon request.

Acknowledgments

The authors thank the Research Center for Agro-Bio-EM and Environmental Resources, Jeonju University, for the pesticide residue analysis.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Forests 15 01996 g001
Figure 1. Temporal variation in pesticide residue in branches and needles (see variable time in Table 3 for statistical results). The values were transformed with a square root.
Figure 1. Temporal variation in pesticide residue in branches and needles (see variable time in Table 3 for statistical results). The values were transformed with a square root.
Forests 15 01996 g001
Table 1. Information about the pesticides used in this study and diameter at breast height (DBH) of P. koraiensis.
Table 1. Information about the pesticides used in this study and diameter at breast height (DBH) of P. koraiensis.
PesticidesCompanyCodeDiameter at Breast Height (DBH) of P. koraiensis (Mean ± SD)
Residue AnalysisEfficacy Test
Abamectin DC (1.8%)AP143.20 ± 2.1337.37 ± 6.05
BP239.80 ± 2.9534.97 ± 4.32
Emamectin benzoate EC (2.15%)CP338.00 ± 1.4134.40 ± 4.00
DP459.20 ± 4.9535.31 ± 5.82
EP540.40 ± 2.9834.51 ± 5.48
AP635.60 ± 3.1732.89 ± 6.24
FP747.40 ± 1.9634.94 ± 4.70
Abamectin (1.6%)–acetamiprid (7%) ME (8.6%)GP838.20 ± 1.4334.71 ± 4.65
Abamectin (1.8%)–sulfoxaflor (4.2%) DC (6%)HP944.0 ± 1.6836.03 ± 6.06
Acetamiprid (8%)–emamectin benzoate (2%) DC (10%)HP1042.40 ± 1.8134.31 ± 4.91
Control-Ctrl A43.2 ± 2.13-
-Ctrl B-19.73 ± 3.08
Table 2. Average recoveries and RSDs of detected pesticides in branches or needles spiked at three different concentrations.
Table 2. Average recoveries and RSDs of detected pesticides in branches or needles spiked at three different concentrations.
PesticideBranchNeedle
Recovery (%), (RSD, %)Correlation CoefficientRecovery (%), (RSD, %)Correlation Coefficient
10 μg/kg30 μg/kg50 μg/kg10 μg/kg30 μg/kg50 μg/kg
Abamectin91 (3.2)89 (3.7)89 (2.8)0.999991 (3.4)85 (5.5)89 (2.5)0.9995
Acetamiprid88 (2.0)86 (0.4)84 (0.6)0.9999103 (1.1)85 (1.2)85 (2.8)0.9997
Emamectin benzoate108 (2.1)95 (0.4)91 (0.1)0.9996108 (3.3)110 (3.1)98 (3.5)0.9995
Sulfoxaflor89 (5.2)84 (3.0)83 (3.5)0.999494 (6.9)94 (6.0)94 (5.7)0.9996
Table 4. Effect of position (lower, middle, or upper canopy position) on pesticide residue levels.
Table 4. Effect of position (lower, middle, or upper canopy position) on pesticide residue levels.
CodePesticidedfF Valuep Value
P1Abamectin2, 1170.6870.505
P2Abamectin2, 1170.7950.454
P3Emamectin benzoate2, 1170.4810.619
P4Emamectin benzoate2, 1172.2850.106
P5Emamectin benzoate2, 1174.4540.014 *
P6Emamectin benzoate2, 1173.0920.049 *
P7Emamectin benzoate2, 1175.2510.007 *
P8Abamectin2, 1170.1090.897
Acetamiprid2, 1170.4940.611
P9Abamectin2, 1177.8520.001 *
Sulfoxaflor2, 1173.310.040 *
P10Emamectin benzoate2, 1171.9510.147
Acetamiprid2, 1171.7860.172
Square root-transformed residue values based on sampled height were analyzed via ANOVA with a 5% error rate. * indicates a significant difference.
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MDPI and ACS Style

Kim, M.-J.; Kim, J.; Yoo, N.S.; Jung, J.-K. Spatiotemporal Dynamics of Trunk-Injected Pesticide Residue for Management of Pine Wilt Disease in Pinus koraiensis. Forests 2024, 15, 1996. https://doi.org/10.3390/f15111996

AMA Style

Kim M-J, Kim J, Yoo NS, Jung J-K. Spatiotemporal Dynamics of Trunk-Injected Pesticide Residue for Management of Pine Wilt Disease in Pinus koraiensis. Forests. 2024; 15(11):1996. https://doi.org/10.3390/f15111996

Chicago/Turabian Style

Kim, Min-Jung, Junheon Kim, Nam Sik Yoo, and Jong-Kook Jung. 2024. "Spatiotemporal Dynamics of Trunk-Injected Pesticide Residue for Management of Pine Wilt Disease in Pinus koraiensis" Forests 15, no. 11: 1996. https://doi.org/10.3390/f15111996

APA Style

Kim, M.-J., Kim, J., Yoo, N. S., & Jung, J.-K. (2024). Spatiotemporal Dynamics of Trunk-Injected Pesticide Residue for Management of Pine Wilt Disease in Pinus koraiensis. Forests, 15(11), 1996. https://doi.org/10.3390/f15111996

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