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Article

Use of Trans-Anethole Against Hop Flea Beetles in Field Conditions

by
Kateřina Kovaříková
1,*,
Roman Pavela
1,2,3,
Karel Krofta
4 and
Josef Vostřel
4
1
Czech Agrifood Research Center, Drnovská 507, 161 06 Prague, Czech Republic
2
Department of Plant Protection, Czech University of Life Sciences Prague, Kamýcká 129, Suchdol, 165 00 Prague, Czech Republic
3
Department of Plant Biotechnology, College of Life Sciences and Biotechnology, Korea University, Seoul 02841, Republic of Korea
4
Hop Research Institute Co., Ltd., Kadaňská 2525, 438 01 Žatec, Czech Republic
*
Author to whom correspondence should be addressed.
Agronomy 2025, 15(6), 1311; https://doi.org/10.3390/agronomy15061311
Submission received: 5 May 2025 / Revised: 23 May 2025 / Accepted: 25 May 2025 / Published: 27 May 2025
(This article belongs to the Section Pest and Disease Management)
Browse Figures
Versions Notes

Abstract

:
In the present study, the effect of two different formulations (NCH1 and NCH2) of trans-anethole was examined against hop flea beetles, Psylliodes attenuatus in field conditions. Products were applied in different locations in the spring seasons of 2019–2021. In 2019, 0.5% and 1% concentrations of both formulations were used so that the effective field dose could be determined. Doses of 1% for both formulations were shown to be more efficient. In 2020, experiments with this dose were carried out in two localities in order to select a more suitable formulation of the product (NCH1 vs. NCH2). The NCH1 formulation was shown to be more effective. After application, there was a significant reduction in the number of flea beetles compared to the control (p < 0.0001). On the other hand, no significant difference was found between the non-treated plot and the NCH2 formulation. In the third year of the experiment (2021), it was found that the number of P. attenuatus on plants treated with NCH1 encapsulation was significantly lower than in the untreated control (p < 0.0001). Residues of trans-anethole degraded immediately; thus, the product is suitable for use in the summer to protect the hop cones before harvest.

1. Introduction

The cultivation of hops (Humulus lupulus L.) has been a traditional branch of agricultural production in Bohemia for over a thousand years [1]. There is written evidence of cultivation of hops in Bohemia, Slovenia and Bavaria from the 9th to the 12th century, and it is assumed that these areas were the centre from where the cultivation of hops spread to the rest of Europe, or even the world [2]. Czech hops are demanded for the best-quality beer and have minority applications in other food and pharmaceutical products (use of β-acids). Nevertheless, with the transition to modern methods of plant cultivation in the mode of ecological or low-residual production, protection of hops from pests has faced new challenges, notably due to missing options for interventions against flea beetles in ecological production. This study presents the results of three years of experiments in field conditions observing the effectiveness of a potential botanical pesticide based on trans-anethole.
Trans-anethole is the main component of essential oils from the seeds of plants such as fennel (Foeniculum vulgare Mill.) [3,4,5,6,7] or anise (Pimpinella anisum L.) [8]. Trans-anethole is characterised by antimicrobial effects [5,9,10] and also shows repellent to toxic effects on some beetle species [11]. In particular, ref. [7] found that essential oil from Foeniculum vulgare was highly efficient against the pollen beetle, Meligethes aeneus Fabricius (Coleoptera: Nitidulidae), in a tarsal test. Ref. [12] reported on toxicity against Sitophilus zeamais Motschulski (Coleoptera: Dryophthoridae). Trans-anethole is generally recognised as a safe agent (GRAS) [13] and is used in the preservation of foodstuffs.
The hop flea beetle Psylliodes attenuatus Koch (Coleoptera: Chrysomelidae) is a tiny beetle detrimental to leaves and hop cones. It is native to the Palearctic region from Eastern Asia to Western Europe [14] but has recently been first detected in Canada, where it has caused substantial damage in some hop gardens [15]. Adult hop flea beetles hibernate and attack emerging plants in spring, perforate leaves and damage the growing buds of hops essentially immediately as soon as the first spring sprouts appear above ground. During a strong occurrence, leaves are reduced to skeletons, resulting in reduced photosynthesis and retarded growth of the hops, which can be particularly dangerous for young plants. New-generation beetles hatch in summer and damage primarily cones, which wither. During the strong occurrence of the summer generation of flea beetles, serious yield loss results. Cones damaged by feeding flea beetles are a gateway for fungal diseases, primarily the downy mildew of hop and the powdery mildew of hop.
In the past, the hop flea beetle was among the major hop pests [16,17] but lost its importance and gained the status of a minority pest with the onset of broad-spectrum insecticides and other management changes. The situation has been reversing lately. Broad-spectrum insecticides have been replaced with selective ones in hop gardens; however, they have a minimal impact on non-target pests, which has enabled the return of formerly important pests [18] and a rise in the harmfulness of some new ones [19]. Elsewhere in Europe, P. attenuatus populations have resurged to sometimes damaging levels on commercial hop crops [17,18,20]. The harmfulness of the hop flea beetle has been on the increase for a long time [20], particularly in connection with warming and shifting boundaries of species range. Arthropod communities reflect the climate, landscape and management methods [21]. The management method (ecological vs. conventional) is one of the prerequisites for the higher occurrence of the flea beetle in hop gardens.
The objective of an intervention against the hop flea beetle is to prevent damage to young hop plants in spring, also resulting in a reduction in the summer population [22], thus smaller damage to hop cones. This makes it possible to retain production quality and maintain competitiveness in the global market. The beetles do not migrate far and are usually found about a mile from infested fields [23], so any local reduction in the P. attenuatus population has a significant impact. Treatment is recommended when the invasion reaches a medium level, corresponding to damage to >5% of the leaf surface [20]. According to the Register of Plant Protection Products [24], the permitted product against the hop flea beetle with conventional management is Exirel, based on cyantraniliprole, for which, however, some major importers of Czech hops (China, Japan, Republic of Korea) do not have a maximum residue limit (MRL). Actara 25 WG (thiamethoxam) was permitted for the last time in 2023 as an exemption; it had the necessary MRL, but as it is a neonicotinoid, its continued use in the EU is unsustainable. Therefore, it is necessary to find an adequate replacement for these products. Refs. [25,26] said that up to 6 million flea beetles may hatch annually in areas without application of thiamethoxam. The situation in ecological production is critical because no sufficiently effective plant protection product is available. Mechanical protection methods fail to lead to a significant reduction in the numbers of flea beetles [17]. The most elegant solution for ecological farming is installing yellow Moericke’s traps combined with a specific attractant for P. attenuatus, which has not been identified yet [27]. So, no plant protection product is currently authorised for controlling the hop flea beetle in organic production.
Alternative protection methods require a comprehensive view of the issue and a solution that exploits a combination of all the available protection options, particularly prevention and correct farming practices, plus biological, mechanical or physical methods. There are many products on the market based on so-called botanical pesticides, particularly plant oils. Around 175 active biopesticide substances were registered worldwide, and around 700 products were available in 2011 [28]. However, their more massive application in field conditions is not common. Thus, the use of “biopesticides” is limited in practice mostly to active substances such as spinosad, pyrethrum and neem derivatives [29].
Plant essential oils are an important natural source of pesticides; they are secondary metabolites enriched with compounds based on the isoprene structure [30]. They are most commonly obtained from medicinal herbs such as basil, rosemary and fennel. They are regarded as effective, yet environmentally considerate, because they are not persistent in ecosystems, which they do not burden with residue. They are also harmless to human health and other animals. Ref. [31] summarised a number of toxic effects of essential oils on insects and acarids, such as antifeedance [32], repellent effects [33], contact effects [34,35,36], and feeding or fumigation toxicity [37,38]. The advantage of plant preparations consists of the fact that they are a mixture of diverse active substances; moreover, they can have synergic effects in suitable combinations.
What is regarded as an advantage from the environmental point of view (low persistence) is an obstacle to practical use. The instability of essential oils when exposed to weather effects, notably accelerated degradation due to UV radiation, may discourage most farmers, because the field application usually has to be repeated. Nevertheless, the drawbacks of essential oils (insolubility in water, low physiochemical stability, oxidation, etc.) can be resolved by producing an inclusive complex—by complexing with cyclodextrins (CDs) in aqueous solutions [39]. There is continuous improvement to formulations intended to fortify the oil service life, such as the micro- and nano-encapsulation techniques used, e.g., in the medicine, food and cosmetics industries [40].
The objective of the present study was to evaluate the effectiveness of the encapsulates NCH1 and NCH2 based on trans-anethole in field conditions and to assess whether such preparations have a potential for practical protection against the hop flea beetle.

2. Materials and Methods

Trans-anethole (Figure 1) (AT, purity > 99%) and β-cyclodextrin (β-CD, purity > 98%) were purchased from Sigma-Aldrich spol. s.r.o. (Prague, Czech Republic). All other chemicals were of analytical grade and purchased from Penta s.r.o. (Prague, Czech Republic).

2.1. Preparation of β-CD/AT Inclusion Complex (NCH1) and AT/β-CD Physical Mixture (NCH2)

The AT and β-CD inclusion complex was produced by the co-precipitation method [41,42] with minor modifications to allow for an increase in the quantity of the preparation. 770 g of β-CD was dissolved in 1200 mL of ethanol/distilled water (1/2, v/v). Then, 100 g of AT was added to the β-CD while stirring constantly at 30 °C. The resulting mixture was blended with a blender for 3 h (150 rpm) at below 20 °C and stored in a cold and dark place until the application. The whole complex was applied without drying, which would be a significant energy input and thus an expenditure.
A physical mixture of AT and β-CD was used as a control group against the inclusive complex. The physical mixture was produced by kneading 770 g of β-CD with 1000 g of AT until a homogeneous mixture was achieved. For the field application, both preparations were stirred into water to obtain a 1% (or 0.5%) solution. Control (kk) was unsprayed.

2.2. Experimental Sites

Field experiments were set up in the spring season of 2019, 2020 and 2021 in hop gardens at three different locations in the Louny district, northwestern Bohemia. See Table 1 for details.
Location no. 1 (50°16′6.745″ N, 13°47′1.686″ E), conventional management. The location belongs to climate region 4—moderately warm, dry (average annual temperature 7–8.5 °C, average precipitation total 450–550 mm). Location 2 (50°19′16.854″ N, 13°37′50.466″ E) and location 3 (50°18′51.002″ N, 13°47′21.211″ E) are fields with organic management. Both localities belong to climatic region 1—warm, dry (average annual temperature 8–9 °C, average precipitation total under 500 mm). Average temperatures and precipitations on experimental sites during the experiment are summarised in Table 2.
The trials were performed on fine-aroma cultivars—Saazer clone no. 72 and Premiant (hybrid cultivar), which were grown in the classical way on 7 m high wire work. Common agro-technical interventions related to hop growing were carried out in the experimental gardens in cooperation with the Hop Research Institute in Žatec, Czech Republic and the cooperative farm in Ročov.

2.3. Experimental Design

The experimental hop gardens in both locations were divided into equally large pieces based on the number of variants. The position of the different variants in the experimental areas changed between years. A simplified diagram of the experiment layout and orientation of fields and rows to cardinal directions is shown in Figure 2. While the experimental hop gardens no. 2 and 3 stand alone in the landscape, the hop garden no. 1 is a part of a larger block that extends to the left of the NCH1l variant.
The objective of the experiment in the first year was, above all, to determine the effective concentrations of both experimental preparations NCH1 and NCH2. Two concentrations were chosen as follows: low (l = 0.5%) and high (h = 1%) with a dose of 400 L of water/ha. The preparations were applied in accordance with the methodological recommendation [20,43], as the optimal timing of the intervention against the spring generation of the hop flea beetle is the mass hatching period, i.e., typically the first May decade. In the following years, we studied the difference between the variants and their impact on the quantities of the hop flea beetle and on hop leaf damage.

2.4. Data Collection

Direct counts of adult beetles were made by visual inspection of randomly chosen plants (n = 30 in 2019, n = 20 in 2020 and 2021) in four different sections of each treated plot (in total n2019 = 120 and n2020,2021 = 80 plants per treatment). The total number of analysed values was 2840. Plants around the edges (of the field or treatments) were avoided. Sampling days were usually day 0 (before treatment) and 3, 7, 14 and 21 days after the application of encapsulates. Sampling was performed in the morning, when the beetles were not yet active. Data were given as the number of flea beetles per plant. For each inspected plant, the number of leaves was also recorded, and the degree of damage was determined on a pre-defined scale from 1 to 3. Degree 1 = slight damage (<5% leaf area damage); degree 2 = medium damage (5–10% leaf area damage); and degree 3 = severe damage (>10% leaf area damage). The scale was taken from [20]. In practice, spraying is recommended if the damage reaches degree 2.

2.5. Data Analysis

The data were analysed using a generalised linear model (GLM) with a negative binomial distribution. Two factors—spray variant and sampling day—were included in the model in 2019. The location factor was added in 2020. Only the variants “treated” and “untreated” were compared in 2021, the layout being inverse from that in 2020. The data analysis was performed in R software, version 4.4.2 [44]. The standard significance level was determined as p = 0.05. The analysis employed the packages MASS [45], multcomp [46], emmeans [47], DHARMa [48] and sciplot [49]. The statistical analysis, including the flea beetle numbers, used data up to the seventh day of the sampling because a later trans-anethole residue analysis revealed that the residual effectiveness after this period is minimal. Leaf damage data were also processed in R.

2.6. Trans-Anethole (AT) Residues Analysis

2.6.1. Sample Preparation and Optimisation of HS-SPME Parameters

The headspace solid-phase micro-extraction (HS-SPME) method was developed to analyse anethole residues on hop leaves. The optimisation of the various parameters (choice of suitable fibre coating, extraction temperature and time) was performed by choosing conditions that have been shown to obtain the maximum response in terms of analyte peak area [50]. For analysis, a sample of frozen hop leaves (1.00 ± 0.01 g) was placed into a 4 mL glass vial. The vial was tightly closed with a silicon aluminium septum. Before extraction, samples were thawed at 20 °C for 15 min, and the fibre was conditioned for 30 min in a gas chromatograph injection port at 250 °C. Subsequently, SPME fibre was manually inserted into the vial headspace for extraction. In the optimised method, the analyte was absorbed for 30 min at 50 °C in a headspace with PDMS/DVB 65 μm fibre (Supelco). After extraction, the fibre was desorbed onto the split/splitless injector of the gas chromatograph [51].

2.6.2. GC/MS Analysis

Anethole was analysed using the Thermo Trace 1300 (Thermo Fisher Scientific S.p.A., Milan, Italy) gas chromatograph with a single quadrupole mass spectrometer Thermo ICQ 7000 (Thermo Fisher Scientific S.p.A., Milan, Italy). SPME fibre containing adsorbed anethole was manually introduced into the GC injection port and kept for 3 min at 250 °C for desorption. The split/splitless injector operated in splitless mode. A specially designed 1.0 mm injector liner was used to prevent peak broadening. The analytical capillary column was Rxi-5Sil MS (30 m × 0.25 mm i.d. × 0.50 mm film thickness, Restek Corporation, Bellefonte, PA, USA). The carrier gas was helium at a constant pressure of 55 kPa. The GC column was held at 60 °C for the first minute of run time, followed by a ramp of 2 °C/min to 170 °C, 5 °C/min to 225 °C and 25 °C/min to 250 °C (hold 5 min) [52]. Under these chromatographic conditions, the elution time of trans-anethole was 36.9 min. The analyte was identified by analytical standard, retention time and mass spectrum.

2.6.3. Preparation of the Trans-Anethole Calibration Line on Hop Leaves

An exact volume of dilute trans-anethole solution (ethanol–water 1:100) was added to a sample of untreated frozen hop leaves (1.0 ± 0.01 g) using a calibrated micropipette so that the absolute amount of analyte added was 50, 100 and 200 ng. After the addition of the standard, the vial was capped, and exposure in the headspace above the sample was initiated after insertion of the SPME fibre. After exposure, the fibre was desorbed in the standard manner in the injection port of the gas chromatograph. The analytical signal was quantified as the area of the trans-anethole chromatographic peak. The calibration line is linear in the concentration range of 50–200 ng.

2.7. Monitoring of the Hop Flea Beetle in Hop Gardens in Summer

An approximate monitoring of the hop flea beetle in hop gardens was carried out in 2021–2024. The selected locations also included fields where spring flea beetle experiments had taken place in 2019–2021. These three locations were extended in 2024 with another 11 randomly selected sites so as to cover the area between Žatec, Rakovník and Louny evenly, if possible. Out of the 14 sites, 2 were managed under organic agriculture. The monitoring was made on 17 and 18 July 2024, which was a period with an abundance of flea beetles. The monitoring was carried out by beating onto white linen (1 × 1 m) with three taps on the hop vine. The number of beetles was recorded in a report on the spot. On each site, 10 plants in 4 different parts of the hop gardens were assessed. Edges of the hop gardens were omitted (approx. 20–30 m).

3. Results

3.1. Number of Hop Flea Beetles

In 2019, the average number of beetles per plant three days after the treatment was the highest for the variant NCH1l (0.38), followed by the control (0.31), NCH2l (0.28), NCH2 (0.19) and NCH1 (0.16). Seven days later, the most beetles were in the control (0.37), followed by NCH1l (0.34), NCH2l (0.27), NCH1 (0.18) and NCH2 (0.16). Beetle numbers differed significantly among treatments (glm.nb, χ22 = 150.305; p < 0.0001). The assessment day or interaction between the two factors was not significant (glm.nb, χ21 = 0.000; p = 1.000; glm.nb, χ24 = 1.453; p = 0.835) and was removed from the model using the update method.
Based on a post hoc analysis, it was found that the beetle numbers in both spray variants with a 1% concentration differed from the control and from NCH1-l (p < 0.005); see Figure 3.
In 2020, the average initial numbers of beetles on location 3 were higher than on location 2. Specifically, the untreated part of the hop garden had an average of 4.1 and 1.9 beetles per plant (locations 3 and 2, respectively); variant NCH1 had 3.9 and 1.8 individuals initially, and NCH2 had 4 and 1.9, respectively. Three days after the treatment, the control had 1.7 and 1.5 beetles (locations 3 and 2, respectively), variant NCH1 had 0.3 and 0.2 beetles, and NCH2 had 1.4 and 1.1 beetles. On the seventh day, the control had 0.8 and 1.7 beetles, NCH1 had 0.3 and 0.6 beetles, and NCH2 had 0.8 and 1.7 beetles.
Beetle numbers differed significantly among treatments (glm.nb, χ22 = 150.305; p < 0.0001). Significant factors included the day of sampling (glm.nb, χ22 = 239.303; p < 0.0001) and the interaction between the factors treatment/day (glm.nb, χ24 = 73.556; p < 0.0001) and day/location (glm.nb, χ22 = 81.357; p < 0.0001). The effect of the factor location alone was not significant (glm.nb, χ21 = 0.062; p = 0.803). The variant NCH1 had the lowest number of flea beetles. It differed from both the untreated control and from NCH2 on both the third and seventh days after the sampling (Figure 4).
In 2021, we assessed the presence of the flea beetles only on location 2 in the variants “treated” (NCH1) and “untreated” (kk); the two variants were laid out inversely to those of 2020. Sampling days (0 and 7 days), the effect of treatment and interaction between the two factors were statistically significant (glm.nb, χ21 = 131.953; p < 0.0001), (glm.nb, χ21 = 3.96; p < 0.047) and (glm.nb, χ21 = 59.499; p < 0.0001), respectively. In both variants, the number of flea beetles decreased after 7 days; while the decrease was slight only in the control, it was significant in the treated variant (Figure 5).
The average number of imagos of P. attenuatus before the treatment was 1.5 with a maximum of 7 ex./plant (NCH1) and 1.2 with a maximum of 6 individuals per plant (untreated plot). After the treatment, the average was 0.14 with a maximum of 2 and 0.9 with a maximum of 5 ex./plant (respectively).
A complete overview of results during the three years of field experiments is shown in Table 3.

3.2. Degree of Damage of Hop Leaves

The average leaf damage in 2019 (day 3) corresponded to level 2 for preparation NCH1l and was on the border of level 2 for NCH1. The plants in the control and in both variants of the preparation NCH2 were at level 1. When evaluated after 14 days, a slight decrease in damage was recorded for NCH1, while the damage increased in the other variants. The largest increase in damage was recorded in the control. The resulting damage was at level 2 for the variants NCH1l, NCH2l and the control. The variants NCH1 and NCH2 were rated as level 1 (Figure 6).
In 2020, the initial damage was at the borderline of level 3 for the NCH1 and control variants. Damage for the NCH2-treated variant was at level 2. After 14 days, the damage had decreased for all the variants: to level 2 for the untreated control, to level 1 for NCH1, and for NCH2, the level remained the same. The largest decrease in damage was observed for the NCH1 variant. Data from both locations are grouped together because there was no significant difference between them (Figure 7).
In 2021, location 2 recorded a decrease in damage in the treated variant, while the situation worsened slightly in the control. The assessment was made after 13 days (Figure 8). At the beginning, the plant damage was at level 1 for the control and at the border of level 2 for NCH1. At the end, the assessment of both variants was at level 1.

3.3. Detection of Trans-Anethole on Hop Leaves

The frozen hop leaf samples were analysed in the same way as the calibration samples. The weight to be analysed was always 1.00 ± 0.01 g. Samples taken on a total of 9 sampling dates (2 h, 24 h, 3, 7, 14, 21, 28, 35 and 42 days after application) were analysed. The analyses were performed in duplicate, and the results of positive findings are expressed as the arithmetic mean of the two determinations. Trans-anethole was found on the surface of hop leaves only for the first three days after application; after this time all other findings were negative. The amount of anethole ranged from approximately 30 to 60 ng/g, i.e., 30–60 μg/kg (Figure 9). Negative findings at later dates could have been due, among other things, to warmer weather towards the end of May and during June.

4. Discussion

In 2019, on location 1, it was impossible to rule out a gradient in the numbers of flea beetles from NCH1l to the left towards NCH2 (Figure 2, experimental design scheme). The beetles might have spread from the immediately adjacent hop garden on the left, also due to the prevalent western and southwestern winds. This is only a conjecture, but the obtained results point to it. At any rate, it is evident that the variant NCH1 had a dramatically higher percentage of flea beetles than both adjacent plots, attesting to the effect of the preparation used. Results from 2020 and 2021 also indicate the success of this variant because the layout of the variants in the fields kept changing, and the effect of treatment under various conditions (locations, row orientation to cardinal directions, surroundings of hop gardens, soil conditions, altitude) was proven.
Locations 2 and 3 are relatively similar to each other in terms of climatic characteristics. Both locations are rather warmer and drier. The surrounding landscape is also similar for these hop gardens, with the difference that there are other agricultural crops nearby around the hop garden at location 2, while there is another hop garden nearby at location 3. The most flea beetles were also found at location 3 during the experiment. The surrounding vegetation, the presence of agricultural crops, possible isolation from the surroundings and the intensity of management have a significant impact on the formation of ecosystem functions, including the regulation of harmful species in agroecosystems [21,54]. On the contrary, location 1 is relatively cold and rainy. On one side, the hop garden is directly adjacent to a forest, which can create a certain barrier against the invasion of hop beetles from the surrounding area. On the other side, there are large areas of hop gardens, but they are managed conventionally, so the abundance of hop flea beetles is relatively low. This also corresponds to the recorded data—location 1 had the fewest flea beetles during the experiment. Unfortunately, we do not have enough data for more detailed analyses. The experiment at locations 1 and 3 ran for only one year, and it is not possible to draw relevant conclusions from this. It is generally known that hop beetles thrive better in warm and drier weather, which is why their harmfulness, along with a change in the spectrum of active substances, increases [43].
In 2020, on location 3, more than 90% of the plants were indicated to host flea beetles at the start of the experiment. When the plants were small (max. 1 m high, BBCH 32), up to 13 beetles were counted on one plant, with an average of 3 beetles per plant, which was the highest population density identified. For a comparison, the average number of flea beetles per plant in 2019 was only 0.5, with a maximum of 8 individuals on one plant. In location 2 in 2020 and 2021, the average was 1.9 and 1.4 ex./plant with a maximum of 8 and 7 individuals.
The best results compared to the untreated control were achieved in 2020, when an average of 1.5 individuals per plant were found in the untreated part of the hop garden, while it was 0.3 beetles three days after the treatment for NCH1, which is five times less. Considering 2924 hop plants per hectare [55], this corresponds to 4386 beetles/ha in the control and 877 beetles in the treated variant. This difference may have a practical impact on the plant damage level, which is critical for the treatment application. After the treatment, the damage fell below the harm threshold in all four cases of the variant NCH1 (resulting damage level 1).
The hop cultivar also plays an important role in the food preferences of the hop flea beetles; some are more attractive than others, but, in general, it prefers cultivated hops to wild ones [56]. The effect of the cultivar could not be assessed because most of all areas were planted with the Saazer cultivar. At location 2, there is a mixed planting of the Saazer and Premiant cultivars, but we do not have enough data to assess. Based on observations in the field, it is possible that the Premiant cultivar is more sensitive to flea beetles, which may also be due to agrotechnical interventions (time of pruning).
Given the current limited options for protection against the hop flea beetle [17,25,26,27], particularly in organic production, the NCH1 encapsulate can be considered a relatively promising preparation that could also find application in the production of industrial hemp, which, for example, has been experiencing a boom in EU countries in recent years [57]. Nevertheless, it is still only an experimental case and a potential suggestion for registering a “fennel” preparation in the future. The mode of action of the tested preparation may be both repellent and antifeedant [7]. Although trans-anethole also has insecticidal effects on some insect species [58], we assume that the contact effect is weakened under field conditions, also due to difficulty in reaching the flea beetles with the spraying, because they either jump away or are not active and hide outside the reach of the spray. On the other hand, we expect that the biological efficacy of the synthetic insecticides based on cyantraniliprole (Exirel) or lambda-cyhalothrin (Karate Zeon 5 CS), which is stated to be approximately 60–70% and 40–60% [59], respectively, is likely to be higher than that of alternative products such as the encapsulate we tested. Ref. [59] also reports field efficacy after Abbott’s correction for some of the alternative products they tested, such as seaweed-based fertilisers, in the range of approximately 17–41% and 15–42% for phyllosilicates. However, the use of synthetic insecticides in organically managed hop gardens is not permitted.
The damage threshold was achieved in at least one part of the hop garden in each year of the spring experiment. That said, the highest numbers of flea beetles were recorded on location 3 (organic management) in 2020. High abundance of hop flea beetles was also observed at this location during summer monitoring in 2021–2023, namely 9–14 individuals per plant, whereas there were only 1–4 individuals in location 1 (conventional) in the same period. In 2024, the average numbers of flea beetles in most of the conventional hop gardens (8 out of 12) were up to 2 ex./plant. In two (extreme) cases, there were 7 and 11 individuals, and in two other hop gardens, there were 3 and 4 individuals per plant, while there were 6 and 10 flea beetles per plant in the two ecological hop gardens. It follows from the results that the beetle ratio (treated/untreated or conventional/ecological) remains roughly the same, namely 1:5. Nevertheless, these are only the beetles that could be registered by the beating; in reality, there will be many more beetles in the hop garden. Refs. [25,26] said that one hectare of ecological hop garden provided the potential for up to 6 million flea beetles to hatch. That said, there is no realistic way of eliminating the pest effectively in organic agriculture. The flea hop beetle Psylliodes attenuatus has recently been first detected in Canada, where growers estimated yield losses of at least 10–15% in heavily infested hop gardens. In some hop gardens, every third cone contained a feeding P. attenuatus beetle [15]. It is evident that some locations are more threatened by the hop flea beetle than others. In the Tršice hop-growing area, the damage threshold was reached in only one of the three monitored hop gardens in 2022 [60]. However, it can be assumed that the situation is going to worsen steadily everywhere because the growing harmfulness of the hop flea beetle has been observed for a long time [20,61].
For possible practical use, we recommend repeating the spraying after 14 days. Its effect can also be enhanced with a wetting agent; however, we have not tested this. Rapid degradation of the active ingredient is certainly desirable from an ecological point of view and from the point of view of pesticide residues [62]. Given the effectiveness of the protective measure, this is no longer so desirable; however, it is quite common with alternative plant-based preparations. It is also possible that trans-anethole degraded more rapidly due to adverse weather conditions after application; however, residues are not expected to be detectable after more than 7 days. For this reason, we assessed the number of flea beetles only up to the 7th day after spraying. After this date, we assume that their population in the hop garden begins to replenish. This is also confirmed by data from subsequent sampling. On the contrary, when assessing leaf damage, we assumed that it takes the plant a while to recover and for new, undamaged leaves to start growing. Based on experience from field sampling, it is approximately 14 days. After that, the treatment needs to be repeated. No phytotoxicity was observed during field applications, but it is possible that it could occur at higher product concentrations. On the other hand, research [63] reports that no phytotoxicity was observed on weeds treated with trans-anethole even at higher concentrations. Encapsulates had no visible effect on hop growth.

5. Conclusions

We found that the trans-anethole-based encapsulate labelled NCH1 at 1% concentration showed a significant reduction in the number of flea beetles compared to the untreated control. The effect of this treatment also affected the degree of plant leaf damage, which was reduced below the harmful threshold within 14 days. The positive effect was observed in three different years and under different conditions. Even though the result is statistically significant, it is not clear whether the effect will be sufficient under high population densities of P. attenuatus. Therefore, it will be very important to continue searching for new substances that would be able to reduce the high numbers of flea beetles, which are a threat not only in several organically managed hop gardens but are likely to spread in conventional production as well.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/agronomy15061311/s1.

Author Contributions

Conceptualization, R.P. and J.V.; methodology, K.K. (Kateřina Kovaříková), R.P., J.V. and K.K. (Karel Krofta); formal analysis, K.K. (Kateřina Kovaříková) and K.K. (Karel Krofta); investigation, K.K. (Kateřina Kovaříková); resources, R.P.; data curation, K.K. (Kateřina Kovaříková) and K.K. (Karel Krofta); writing—original draft preparation, K.K. (Kateřina Kovaříková); writing—review and editing, J.V., K.K. (Karel Krofta) and R.P.; visualization, K.K. (Kateřina Kovaříková); supervision, R.P. and J.V.; project administration, R.P. and J.V. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Ministry of Agriculture of the Czech Republic within the Institutional Support MZE-RO025 and MZE-RO1325.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author, dataset_file.v1.xlsx.

Acknowledgments

We are grateful to Václav Pálek for his enormous help in collecting data in the field. We would also like to thank Silvie Bělašková for valuable advice on statistical analysis. Finally, we also thank EKO Překlady s.r.o. for the translation and Greg Edwards for the English proofreading of the manuscript.

Conflicts of Interest

Authors Karel Krofta and Josef Vostřel are employed by the company Hop Research Institute Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

References

  1. Beranová, M.; Kubačák, F. Dějiny zemědělství v Čechách a na Moravě; Libri: Praha, Česká Republika, 2010. [Google Scholar]
  2. Neve, R.A. Hops. Springer: Bury St. Edmunds, UK, 1991. [Google Scholar] [CrossRef]
  3. Marotti, M.; Piccaglia, R.; Giovanelli, E.; Deans, S.G.; Eaglesham, E. Effects of variety and ontogenic stage on the essential oil composition and biological activity of fennel (Foeniculum vulgare Mill.). J. Essent. Oil Res. 1994, 6, 57–62. [Google Scholar] [CrossRef]
  4. Stefanini, M.B.; Ming, L.C.; Marques, M.O.M.; Facanali, R.; Meireles, M.A.A.; Moura, L.S.; Marchese, J.A.; Sousa, L.A. Essential oil constituents of different organs of fennel (Foeniculum vulgare var. vulgare). Rev. Bras. Pl. Med. 2006, 8, 193–198. [Google Scholar]
  5. Gulfraz, M.; Mehmood, S.; Minhas, N.; Jabeen, N.; Kausar, R.; Jabeen, K.; Arshad, G. Composition and antimicrobial properties of essential oil of Foeniculum vulgare. Afr. J. Biotechnol. 2008, 7, 4364–4368. [Google Scholar]
  6. Chowdhury, J.U.; Mobarok, M.H.; Bhuiyan, M.N.I.; Nandi, N.C. Constituents of essential oils from leaves and seeds of Foeniculum vulgare Mill. cultivated in Bangladesh. Bangladesh J. Bot. 2009, 38, 181–183. [Google Scholar] [CrossRef]
  7. Pavela, R. Insecticidal and repellent activity of selected essential oils against of the pollen beetle, Meligethes aeneus (Fabricius) adults. Ind. Crops Prod. 2011, 34, 888–982. [Google Scholar] [CrossRef]
  8. Orav, A.; Raal, A.; Arak, E. Essential oil composition of Pimpinella anisum L. fruits from various European countries. Nat. Prod. Res. 2008, 22, 227–232. [Google Scholar] [CrossRef]
  9. Morris, J.A.; Khettry, A.; Seitz, E.W. Antimicrobial activity of aroma chemicals and essential oils. J. Am. Oil Chem. Soc. 1979, 56, 595–603. [Google Scholar] [CrossRef]
  10. Curtis, O.F.; Shetty, K.; Cassagnol, G.; Peleg, M. Comparison of the inhibitory and lethal effects of synthetic versions of plant metabolites (anethole, carvacrol, eugenol, and thymol) on a food spoilage yeast (Debaromyces hansenii). Food Biotechnol. 1996, 10, 55–73. [Google Scholar] [CrossRef]
  11. Alkan, M.; Ertürk, S. Insecticidal Efficacy and Repellency of Trans-Anethole Against Four Stored-Product Insect Pests. J. Agric. Sci. 2020, 26, 64–70. [Google Scholar] [CrossRef]
  12. Bertoli, A.; Conti, B.; Mazzoni, V.; Meini, L.; Pistelli, L. Volatile chemical composition and bioactivity of six essential oils against the stored food insect Sitophilus zeamais Motsch. (Coleoptera Dryophthoridae). Nat. Prod. Res. 2012, 26, 2063–2071. [Google Scholar] [CrossRef]
  13. Newberne, P.; Smith, R.L.; Doull, J.; Goodman, J.I.; Munro, I.C.; Portoghese, P.S.; Wagner, B.M.; Weil, C.S.; Woods, L.A.; Adams, T.B.; et al. The FEMA GRAS assessment of trans-anethole used as a flavouring substance. Food Chem. Toxicol. 1999, 37, 789–811. [Google Scholar] [CrossRef] [PubMed]
  14. Döberl, M. Alticinae. In Catalogue of Palearctic Coleoptera; Löbl, C.I., Smetana, A., Eds.; Appolo Books: Stenstrup, Denmark, 2010; Volume 6, 924p. [Google Scholar]
  15. Douglas, H.B.; Renkema, J.; Smith, T.W.; Konstantinov, A.S.; Serres, J.M.D. Palearctic flea beetle and pest of hops and Cannabis, Psylliodes attenuata (Coleoptera, Chrysomelidae, Galerucinae), new to North America. Biodivers. Data J. 2024, 12, e120340. [Google Scholar] [CrossRef]
  16. Blattný, C. Nomenklatura chorob a škůdců chmele. Ochr. Rostl. 1926, 6, 134–138. [Google Scholar]
  17. Weihrauch, F.; Baumgartner, A.; Eisenbraun, D.; Wolf, S.; Mumm, R.; van Tol, R.W.H.M. Flea-beetle control in organic hops: Are there options? In Proceedings of the Scientific-Technical Commission, International Hop Growers’ Convention I.H.G.C., St. Stefan am Walde, Austria, 25–29 July 2017; Weihrauch, F., Ed.; Hop Research Center: Wolnzach, Germany, 2017; p. 59. [Google Scholar]
  18. Rak Cizej, M.; Žolnir, M. Hop flea beetle (Psylliodes attenuatus Koch) one of the most common hop pests in Slovenia. In Proceedings of the Lectures and Papers of the Sixth Slovenian Plant Protection Congress, Zreče, Slovenia, 4–6 March 2003; pp. 233–238. [Google Scholar]
  19. Campbell, C.A.M. New and resurgent insect pests on low trellis hops. Agric. For. Entomol. 2019, 21, 209–218. [Google Scholar] [CrossRef]
  20. Vostřel, J.; Klapal, I.; Kudrna, T. Metodika Ochrany Chmele Proti Dřepčíku Chmelovému (Psylliodes attenuatus Koch); Chmelařský Institut: Žatec, Slovenia, 2010. [Google Scholar]
  21. Schweiger, O.; Maelfait, J.P.; van Wingerden, W.; Hendrickx, F.; Billeter, R.; Speelmans, M.; Augenstein, I.; Aukema, B.; Aviron, S.; Bailey, D.; et al. Quantifying the impact of environmental factors on arthropod communities in agricultural landscapes across organizational levels and spatial scales. J. Appl. Ecol. 2005, 42, 1129–1139. [Google Scholar] [CrossRef]
  22. Holý, K.; Procházka, P.; Štranc, J.; Štranc, D.; Štranc, P. Integrovaná Ochrana Chmele. Certifikovaná Metodika, 1st ed.; Výzkumný Ústav Rostlinné Výroby, v.v.i.: Praha, Česká Republika, 2017; p. 98. [Google Scholar]
  23. Dmitriev, G.V. Results obtained in studying Psylliodes attenuata Koch, under conditions prevailing in the right bank area of the Kuybyshev district. Plant Prot. 1935, 5, 91–106. [Google Scholar]
  24. Minář, P. Nařízení Ústředního Kontrolního a Zkušebního Ústavu Zemědělského o Povolení Přípravku na Ochranu Rostlin Pro omezené a Kontrolované Použití. ÚKZÚZ. Available online: https://www.syngenta.cz/sites/g/files/kgtney1451/files/media/document/2023/04/04/actara_narizeni-ukzuz-pro-omezene-a-kontrolovane-pouziti-pripravku-actara-25-wg.pdf (accessed on 23 March 2021).
  25. Weihrauch, F. Developing methods pf controlling the hop flea beetle, Psylliodes attenuatus, in organic hop farming: Completion of the project. In Annual Report 2018, Special Crop: Hops; Institute for Crop Science and Plant Breeding, Ed.; Bayerische Landesanstalt für Landwirtschaft: Freising-Weihenstephan, Germany, 2019; pp. 107–111. [Google Scholar]
  26. Weihrauch, F.; Baumgartner, A.; Laupheimer, S.; Mühlbauer, M. Hop-flea beetle revisited: In search for attractants. In Proceedings of the Scientific-Technical Commission, International Hop Growers’ Convention I.H.G.C., Bischoffsheim, Alsace, France, 7–11 July 2019; Weihrauch, F., Ed.; Hop Research Center: Wolnzach, Germany, 2019; p. 70. [Google Scholar]
  27. Mumm, R.; van Tol, R.W.H.M.; Weihrauch, F. Elucidation of the role of volatile compounds in the chemical communication of the hop flea beetle Psylliodes attenuatus. In Proceedings of the Scientific-Technical Commission, International Hop Growers’ Convention I.H.G.C., St. Stefan am Walde, Austria, 25–29 July 2017; Weihrauch, F., Ed.; Hop research Center: Wolnzach, Germany, 2017; pp. 60–64. [Google Scholar]
  28. Kumar, S. Biopesticides: A Need for Food and Environmental Safety. J. Biofertil. Biopestici. 2012, 3, e107. [Google Scholar] [CrossRef]
  29. Dively, G.P.; Patton, T.; Barranco, L.; Kulhanek, K. Comparative Efficacy of Common Active Ingredients in Organic Insecticides Against Difficult to Control Insect Pests. Insects 2020, 11, 614. [Google Scholar] [CrossRef] [PubMed]
  30. Arif, T.; Bhosale, J.D.; Kumar, N.; Mandal, T.K.; Bendre, R.S.; Lavekar, G.S.; Dabur, R. Natural products—Antifungal agents derived from plants. J. Asian Nat. Prod. Res. 2009, 11, 621–638. [Google Scholar] [CrossRef]
  31. Isman, M.B. Plant essential oils for pest and disease management. Crop Prot. 2000, 19, 603–608. [Google Scholar] [CrossRef]
  32. Huang, Y.; Ho, S.H. Toxicity and antifeedant activities of cinnamaldehyde against the grain storage insects, Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch. J. Stored Prod. Res. 1998, 34, 11–17. [Google Scholar] [CrossRef]
  33. Sighamony, S.; Anees, I.; Chandrakala, T.S.; Osmani, Z. Natural products as repellents for Tribolium castaneum Herbst. Int. Pest Control 1984, 26, 156–157. [Google Scholar]
  34. Ho, S.H.; Koh, L.; Ma, Y.; Huang, Y.; Sim, K.Y. The oil of garlic, Allium sativum L. (Amaryllidaceae), as a potential grain protectant against Tribolium castaneum (Herbst) and Sitophilus zeamais Motsch. Postharvest Biol. Technol. 1996, 9, 41–48. [Google Scholar] [CrossRef]
  35. Ho, S.H.; Ma, Y.; Huang, Y. Anethole, a potential insecticide from Illicium verum Hook F., against two stored product insects. Int. Pest Control 1997, 39, 50–51. [Google Scholar]
  36. Gonzalez, M.S.; Lima, B.G.; Oliveira, A.F.R.; Nunesa, D.D.; Fernandes, C.P.; Santos, M.G.; Tietbohl, L.A.C.; Mello, C.B.; Rocha, L.; Feder, D. Effects of essential oil from leaves of Eugenia sulcata on the development of agricultural pest insects. Rev. Bras. Farmacogn. 2014, 24, 413–418. [Google Scholar] [CrossRef]
  37. Shaaya, E.; Ravid, U.; Paster, N.; Juven, B.; Zisman, U.; Pissarev, V. Fumigant toxicity of essential oils against four major storedproduct insects. J. Chem. Ecol. 1991, 17, 499–504. [Google Scholar] [CrossRef]
  38. Regnault-Roger, C.; Hamraoui, A.; Holeman, M.; Theron, E.; Pinel, R. Insecticidal efect of essential oils from mediterranean plants upon Acanthoscelides obtecus Say (Coleoptera: Bruchidae), a pest of kidney bean (Phaseolus vulgaris L.). J. Chem. Ecol. 1993, 19, 1233–1244. [Google Scholar] [CrossRef] [PubMed]
  39. Hedges, A.R. Industrial applications of cyclodextrins. Chem. Rev. 1998, 98, 2035–2044. [Google Scholar] [CrossRef] [PubMed]
  40. Shishir, M.R.I.; Xie, L.; Sun, C.; Zheng, X.; Chen, W. Advances in micro and nano-encapsulation of bioactive compounds using biopolymer and lipid-based transporters. Trends Food Sci. Technol. 2018, 78, 34–60. [Google Scholar] [CrossRef]
  41. Zhang, W.; Li, X.; Yu, T.; Yuan, L.; Rao, G.; Li, D.; Mu, C. Preparation, physicochemical characterization and release behavior of the inclusion complex of trans-anethole and β-cyclodextrin. Food Res. Int. 2015, 74, 55–62. [Google Scholar] [CrossRef]
  42. Wang, J.; Cao, Y.; Sun, B.; Wang, C. Physicochemical and release characterisation of garlic oil-β-cyclodextrin inclusion complexes. Food Chem. 2011, 127, 1680–1685. [Google Scholar] [CrossRef]
  43. Krofta, K.; Ježek, J.; Klapal, I.; Křivánek, J.; Pokorný, J.; Pulkrábek, J.; Vostřel, J. Integrovaný Systém Pěstování Chmele; Metodika pro praxi 02/2012; Chmel. Inst.: Žatec, Česká Republika, 2012. [Google Scholar]
  44. R Core Team. R: A Language and Environment for Statistical Computing; R Foundation for Statistical Computing: Vienna, Austria, 2024; Available online: https://www.R-project.org/ (accessed on 7 April 2025).
  45. Venables, W.N.; Ripley, B.D. Modern Applied Statistics with S, 4th ed.; Springer: New York, NY, USA, 2002. [Google Scholar]
  46. Hothorn, T.; Bretz, F.; Westfall, P. Simultaneous Inference in General Parametric Models. Biom. J. 2008, 50, 346–363. [Google Scholar] [CrossRef] [PubMed]
  47. Lenth, R.V. Emmeans: Estimated Marginal Means, Aka Least-Squares Means; R Package Version 1.10.6. 2024. Available online: https://CRAN.R-project.org/package=emmeans (accessed on 7 April 2025).
  48. Hartig, F. DHARMa: Residual Diagnostics for Hierarchical (Multi-Level/Mixed) Regression Models; R Package Version 0.4.7. 2024. Available online: https://CRAN.R-project.org/package=DHARMa (accessed on 7 April 2025).
  49. Morales, M.; R Development Core Team; Murdoch, D. Sciplot: Scientific Graphing Functions for Factorial Designs; R Package Version 1.2-0. 2020. Available online: https://CRAN.R-project.org/package=sciplot (accessed on 23 May 2025).
  50. Richter, M.T.; Eyres, G.T.; Silcock, P.; Bremer, P.J. Comparison of four extraction methods for analysis of volatile hop-derived aroma compounds in beer. J. Sep. Sci. 2017, 40, 4366–4376. [Google Scholar] [CrossRef] [PubMed]
  51. Saison, D.; De Schutter, D.P.; Delvaux, F.; Delvaux, F.R. Optimisation of a complete method for the analysis of volatiles involved in the flavour stability of beer by solid-phase microextraction in combination with gas chromatography and mass spectrometry. J. Chrom. A. 2008, 1190, 342–349. [Google Scholar] [CrossRef]
  52. Goncalves, J.; Figueira, J.; Rodrigues, F.; Camara, J.S. Headspace solid-phase microextraction combined with mass spectrometry as a powerfull analytical tool for profiling the terpenoid metabolomic pattern of hop-essential oil derived from Saaz variety. J. Sep. Sci. 2012, 35, 2282–2296. [Google Scholar] [CrossRef]
  53. Piepho, H.P. An algorithm for a letter-based representation of all pairwise comparisons. J. Comput. Graph. Stat. 2004, 13, 456–466. [Google Scholar] [CrossRef]
  54. Boháč, J. Biologie Ochrany Přírody Pro Agroekology; JČU: České Budějovice, Czech Republic, 2013; p. 110. [Google Scholar]
  55. Klas, M.; Klas, M.; Klas, Š. Příspěvek k částečné mechanizaci zavádění chmele. Chmelařství 2019, 92, 46–51. [Google Scholar]
  56. Rak Cizej, M.; Milevoj, L. Nutrition Habits of Hop Flea Beetles (Psylliodes attenuatus Koch). In Proceedings of the Zbornik Predavanj in Referatov 8. Slovenskega Posvetovanja o Varstvu Rastlin, Radenci, Slovenija, 6–7 March 2007; pp. 173–178. Available online: https://api.semanticscholar.org/CorpusID:85867624 (accessed on 7 April 2025).
  57. Honsová, H. Technické konopí u nás opomíjené. Úroda 2022, 7, 50–52. [Google Scholar]
  58. Chang, C.L.; Cho, I.K.; Li, Q.X. Insecticidal activity of basil oil, trans-anethole, estragole, and linalool to adult fruit flies of Ceratitis capitata, Bactocera dorsalis, and Bactocera cucurbitae. J. Econ. Entomol. 2009, 102, 203–209. [Google Scholar] [CrossRef]
  59. Rak Cizej, M.; Poličnik, F. Control of hop flea beetle (Psylliodes attenuatus KOCH) on hops (Humulus lupulus L.) using alternative preparations. Hop Bull. 2022, 29, 97–108. [Google Scholar]
  60. Suchánková, M.; Šefrová, H. Škodlivost dřepčíka chmelového v různě starých chmelnicích. Rostlinolékař 2023, 5, 14–16. [Google Scholar]
  61. Rak Cizej, M.; Milevoj, L. Hop flea beetle (Psylliodes attenuatus KOCH) in Slovenia. In Proceedings of the Scientific Commission, International Hop Growers’ Convention, Tettnang, Germany, 24–28 June 2007; Seigner, E., Ed.; Hop Research Center: Wolnzach, Germany, 2017; pp. 91–94. [Google Scholar]
  62. Marrone, P.G. Pesticidal natural products—Status and future potencial. Pest Manag. Sci. 2019, 75, 2325–2340. [Google Scholar] [CrossRef] [PubMed]
  63. Ibáñez, M.D.; Blázquez, M.A. Phytotoxicity of essential oils on selected weeds: Potential hazard on food crops. Plants 2018, 7, 79. [Google Scholar] [CrossRef] [PubMed]
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Figure 1. Structure of trans-anethole.
Figure 1. Structure of trans-anethole.
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Figure 2. Experimental design scheme.
Figure 2. Experimental design scheme.
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Figure 3. Average number of adult P. attenuatus beetles after the treatment in 2019 over both sampling days (3 and 7 days), graph with CI bars; grouping letters (respectively): b, a, b, a, ab.
Figure 3. Average number of adult P. attenuatus beetles after the treatment in 2019 over both sampling days (3 and 7 days), graph with CI bars; grouping letters (respectively): b, a, b, a, ab.
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Figure 4. Average number of adult P. attenuatus beetles after the treatment in 2020 over both locations (locations 2 and 3), graph with CI bars; grouping letters (respectively): e, e, e/d, a, c/c, b, c.
Figure 4. Average number of adult P. attenuatus beetles after the treatment in 2020 over both locations (locations 2 and 3), graph with CI bars; grouping letters (respectively): e, e, e/d, a, c/c, b, c.
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Figure 5. Average number of adult P. attenuatus beetles before and after the treatment with encapsulated NCH1 in 2021, graph with CI bars; grouping letters (respectively): bc, c/b, a.
Figure 5. Average number of adult P. attenuatus beetles before and after the treatment with encapsulated NCH1 in 2021, graph with CI bars; grouping letters (respectively): bc, c/b, a.
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Figure 6. Change in the degree of leaf damage between the 3rd and 14th days in 2019, graph with SE bars.
Figure 6. Change in the degree of leaf damage between the 3rd and 14th days in 2019, graph with SE bars.
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Figure 7. Change in the degree of leaf damage between day 0 and 14 in 2020: both localities are grouped in the graph with SE bars.
Figure 7. Change in the degree of leaf damage between day 0 and 14 in 2020: both localities are grouped in the graph with SE bars.
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Figure 8. Change in the degree of leaf damage between days 0 and 13 in year 2021; graph with SE bars.
Figure 8. Change in the degree of leaf damage between days 0 and 13 in year 2021; graph with SE bars.
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Figure 9. Findings of trans-anethole residues on the surface of hop leaves in 2021.
Figure 9. Findings of trans-anethole residues on the surface of hop leaves in 2021.
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Table 1. Experimental plots.
Table 1. Experimental plots.
LocationAltitudeSoil TypeArea (ha)CultivarSampling Years
1400 mrendzina, pararendzina1.7Saazer2019
2212 mchernozem2.2Saazer/Premiant2020, 2021
3287 mrendzina, pararendzina1.6Saazer2020
Table 2. Average temperature/sum of temperatures and total precipitation on experimental sites during the trials.
Table 2. Average temperature/sum of temperatures and total precipitation on experimental sites during the trials.
Location-YearTemperetures (°C)Precipitation (mm)Duration of the Trial (Day/Month)
1–201912.4/27270.97/5–28/5
2–202011.9/262.459.621/4–13/5
2–202112.5/274.865.610/5–1/6
3–202012.1/265.446.225/4–18/5
Table 3. A complete overview of the results of all performed experiments; numbers represent an average beetle count per plant, and grouping letters indicate a significant difference among the groups according to CLD [53] of all pairwise comparisons of estimated marginal means (p < 0.05).
Table 3. A complete overview of the results of all performed experiments; numbers represent an average beetle count per plant, and grouping letters indicate a significant difference among the groups according to CLD [53] of all pairwise comparisons of estimated marginal means (p < 0.05).
YearLocationkkNCH1lNCH1 NCH2lNCH2 Days
201910.34 (0.27–0.42) b0.36 (0.29–0.44) b0.17 (0.13–0.23) a0.28 (0.22–0.35) ab0.18 (0.13–0.24) agrouped
20202/3 grouped2.82 (2.24–3.56) ex2.69 (2.16–3.35) ex2.74 (2.20–3.40) e0
20202/3 grouped1.61 (1.39–1.87) dx0.25 (0.19–0.33) ax1.24 (1.06–1.47) c3
20202/3 grouped1.20 (1.02–1.42) cx0.42 (0.32–0.54) bx1.19 (1.00–1.40) c7
KkxNCH1
202121.21 (0.97–1.52) bcx1.54 (1.33–1.78) cxx0
202120.88 (0.68–1.13) bx0.14 (0.09–0.22) axx7
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MDPI and ACS Style

Kovaříková, K.; Pavela, R.; Krofta, K.; Vostřel, J. Use of Trans-Anethole Against Hop Flea Beetles in Field Conditions. Agronomy 2025, 15, 1311. https://doi.org/10.3390/agronomy15061311

AMA Style

Kovaříková K, Pavela R, Krofta K, Vostřel J. Use of Trans-Anethole Against Hop Flea Beetles in Field Conditions. Agronomy. 2025; 15(6):1311. https://doi.org/10.3390/agronomy15061311

Chicago/Turabian Style

Kovaříková, Kateřina, Roman Pavela, Karel Krofta, and Josef Vostřel. 2025. "Use of Trans-Anethole Against Hop Flea Beetles in Field Conditions" Agronomy 15, no. 6: 1311. https://doi.org/10.3390/agronomy15061311

APA Style

Kovaříková, K., Pavela, R., Krofta, K., & Vostřel, J. (2025). Use of Trans-Anethole Against Hop Flea Beetles in Field Conditions. Agronomy, 15(6), 1311. https://doi.org/10.3390/agronomy15061311

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