Mistletoe Eradicator - A Novel Tool for Simultaneous Mechanical and Chemical Control of Mistletoe

Summary

The protocol describes an easy-to-handle tool called Mistletoe Eradicator which combines mechanical and chemical approaches and is efficient in the control of mistletoe infestation on the host trees. The manuscript uses the European mistletoe (Viscum album subsp. album L.) as an example.

Abstract

Some species of mistletoes, an aerial plant hemiparasites, play a Janus-like role in ecosystems by being rich biodiversity hotspots due to their trophic and topic associations with various organisms and at the same time acting as biological pirates, exhausting the host trees by stealing water and nutrients via the haustorium. Many crop and timber trees are attacked by mistletoes, for example, dwarf mistletoes parasitize conifers, representatives of genus Tapinanthus target guava, and Phoradendron mistletoe target pecans. Recently, an increasing infestation of the European mistletoe (Viscum album subsp. album L.) in monoculture stands of common walnuts (Juglans regia L.) was recorded for the first time during 2018 in different regions of Kashmir Valley, India. The common chemical approach based on the spraying of mistletoe exophytes with the growth regulators, ethephon and glyphosate, was not efficient since V. album resprouted in the next vegetation season. Hand pruning of mistletoe was time-consuming, and a polyethylene covering resulted in the localized rotting of host tissues. The most efficient approach to eradicate mistletoe was the use of a novel tool called Mistletoe Eradicator, which allows to use mechanical and chemical means of mistletoe control simultaneously. It consists of a manipulating pole with the terminal pruning saw having a container filled with the growth regulator, from which the liquid slowly drops onto the saw blade through the nozzle. It allows working both from the ground and in the tree canopy. After the targeted application of 5%-10% ethephon or glyphosate to the base of the just pruned V. album stems (stubs), exophyte resprouting was significantly reduced 9 months after the pruning as compared to the only pruned or sprayed exophytes. An alternative variant of Mistletoe Eradicator was constructed in Ukraine filled just with a food color additive to track the liquid dropping and was successfully tested.

Introduction

Mistletoes are a taxonomically diverse group of aerial stem hemiparasites belonging to the Loranthaceae, Viscaceae, Santalaceae, Amphorogynaceae, and Misodendraceae families (order Santalales). They attach to the susceptible host trees by a specific anatomical bridge called a haustorium (endophyte) and are largely dependent on the host for water and nutrient supply, but are still able to photosynthesize via the green aerial portion called exophyte^1,2. Although mistletoes may be considered hotspots of diversity providing food and shelter for various organisms, some mistletoe species are indeed biological pirates, affecting host health, fitness, and lifespan by the reducing their annual apical and lateral growth, flowering and fruiting as well as facilitating attacks of biological invaders such as fungi and bacteria^3,4,5. At the same time, mistletoes are intensely used in both traditional and folk medicine, are components of compost, mulch, forage, and act as seasonal ecotourism attractions^6,7,8.

Some of the notorious parasitic mistletoes are the dwarf mistletoes (Arceuthobium spp.; Santalaceae) reducing the growth of coniferous trees in North America⁹ and Mexico¹⁰; Tapinanthus (Blume) Rchb. mistletoes (Loranthaceae) attacking cacao (Theobroma cacao L.) and Citrus L. plantations in Africa^11,12; hairy mistletoes (Taxillus tomentosus (Heyne ex Roth) van Tiegh.; Loranthaceae) affecting the Indian Euphorbiaceae trees, Phyllanthus emblica L. and Phyllanthus indofischeri Bennet, both known locally as Amla¹³; and the European mistletoe (Viscum album subsp. album L.; Viscaceae) having a broad host spectrum (more than 450 tree species)^14,15 and rapidly spreading in Europe with its range shifted northwards¹⁶.

Walnut (Juglans regia L.) is an important horticultural cash crop in Kashmir valley constituting approximately 85% of India's annual walnut production¹⁷. Besides other biotic stresses such as leaf blotch, anthracnose, crown galls, stem cankers, walnut blight, or lace bug (Paracopium cingalense (Walker, 1873); Heteroptera: Tingidae) that attack the walnuts in Kashmir Valley, the V. album, locally called banada, kaw-khoor or nalkachul, also heavily infests these trees and can also rarely parasitize poplars (Populus L.; poplars in Kashmir valley are secondary hosts)¹⁸. Such a localized infestation might be explained by the possible concomitant introduction of V. album at the early developmental stages of 2-3 years, when its exophytes are almost invisible, with the planting material of walnuts from some plant nurseries. In turn, local poplar trees, the widespread susceptible primary host of this mistletoe in Europe, might be attended by birds vectoring sticky viscin-covered mistletoe fruits to the neighboring J. regia orchards.

Besides walnuts, leafy mistletoes parasitize other nut-producing trees, for example, almonds (Prunus dulcis (Mill.) D.A. Webb) are attacked by V. album in the Mediterranean Europe and in Crimea (Ukraine) as well as by the representatives of Phoradendron Nutt. genus in North America^14,15,19; common hazel (Corylus avellane L.) by V. album in Europe^14,15; pecan (Carya illinoinensis (Wangenh.) K.Koch) by oak mistletoe (Phoradendron flavescens (Pursh) Nutt.) in the southeastern United States^20,21, and V. album in Europe¹⁴; macadamia (Macadamia F. Muell.) by shiny-leaved mistletoe (Benthamina alyxifolia (F.Muell. ex Benth.) Tiegh.), concomitant coast mistletoe (Mullerina celastroides (Sieb. ex. Schult & Schult. f.) Tiegh.), erect mistletoe (Amyema congener (Sieber ex Schult. & Schult. f.) Tiegh.), smooth mistletoe (Dendrophthoe glabrescens (Blakeley) Barlow), and long-flowered mistletoe (Dendrophthoe vitelline (Sieb. ex. Schult & Schult.f.) Tiegh.) in Australia²² (Watson, 2018); kolanut (Cola nitida (Vent.) Schott & Endl.) by Phragmanthera incana (Schumach.) Balle and Tapinanthus bangwensis (Engl. & K.Krause) Danser in Nigeria²³; and cashew (Anacardium occidentale L.) by Psittacanthus plagiophyllus Eichler in Amazonian savanna²⁴.

Currently, the strategy of mistletoe control develops in frames of the integrated pest management paradigm combining mechanical, chemical, and biological means to reduce infestations^{4,7,25,26,27,28}. An environmentally friendly mistletoe biocontrol method involves the use of the natural enemies of mistletoe such as bacteria, necrotrophic fungi, herbivores, or even epiparasitic mistletoes^3,4,7,29,30 but have limited applications due to the non-specificity and small-scale of action of the biotic agents. Although cutting and pruning are recognized as the most traditional and efficient means of mistletoe control^26,30,31,32, exophytes frequently resprout. For spraying of mistletoe exophytes with chemicals, mistletoe stubs or host stems are injected with systemic herbicides such as glyphosate, 2,4-dichlorophenoxyacetic acid (2,4-D), 4-(2,4-dichlorophenoxy) butyric acid (2,4-DB), or 2,4,5-trichlorophenoxyacetic acid (2,4,5-T)^3,33 or ethylene-releasing defoliants and ripening enhancers such as ethephon or (2-chloroethyl)-phosphonic acid)^34,35. The combination of exophyte pruning to 2-3 cm stubs along with ethephon application to cut end of mistletoe stubs with a fine brush resulted in reduced V. album resprouting. This inspired the development of Mistletoe Eradicator, which can perform mechanical and chemical control of mistletoe growth simultaneously.

Here, we introduce an easy-to-handle and broadly available tool called Mistletoe Eradicator, which combines the benefits of mechanical and chemical means of mistletoe control and prevents its resprouting. The tool allows the certified arborists, plant pathologists, foresters, horticulturists, silviculturists, plant ecologists, experienced gardeners and other instructed users to deal with mistletoe challenge from the ground, from aerial platforms or from the trees. The tool performs a targeted pruning of mistletoe exophyte with the simultaneous dropping of a small amount of growth regulator directly on the pruned mistletoe stem. Mistletoe Eradicator was patented in India³⁶ and used for the successful control of an increasing V. album subsp. album infestation on walnuts in Kashmir Valley. An updated version of this tool was designed in Ukraine and introduced to local arborists to practice in field tests with just a food color additive to track the herbicide dropping. It is noteworthy that Mistletoe Eradicator can be easily assembled and used for the control of other host-aggressive mistletoe species at the sites of their infestation in accordance with the national environmental law and after the approval of the local human communities.

Protocol

The growth regulators used in the work are available in the market after approval by the Central Insecticide Board (http://ppqs.gov.in/central-insecticides-board). Moreover, personal invitations and permissions of the farmers and owners of walnut plantations, who offered their infected trees for experiments, were obtained. Experiments presented here were done by a certified arborist in the closed research and monitoring zone of M.M. Gryshko National Botanical Garden of National Academy of Sciences of Ukraine (Kyiv, Ukraine). Before starting to work with Mistletoe Eradicator in your country, please check the environmental regulation, get permissions for the use of herbicides from the relevant authorities of the country, where Mistletoe Eradicator will be operated, and obtain agreement on its use with the local human communities (farmers, landowners, etc.).

1. Long-term preparations

1. Briefly introduce yourself or/and other users of Mistletoe Eradicator into the basics of mistletoe biology and ecology, and approaches to its control.
2. Optional: Assess the mistletoe incidence, the degree of infestation, host tree mortality rates, and the degree of mistletoe biotic damage of the host trees (e.g., crone defoliation and water stress in host branches acropetal to mistletoe exophyte) to select the priority of mistletoe control on the most infested host trees based on the approaches described in^{20,30,32,37,38}.
3. Check weather forecast including wind direction and strength, temperature, probability of rain, snowing, fog, or frost with a reliable meteorological service. Operate Mistletoe Eradicator under dry weather and under adequate light conditions to see the working area clearly.

2. Assembly of Mistletoe Eradicator

NOTE: All components of Mistletoe Eradicator are publicly available in supermarkets and gardener stores and are better to be custom-tailored and connected with the help of the professional welding engineer. Details and equipment used for the assembly of Mistletoe Eradicator must be modified and adjusted based on the country of use and availability of the components in an open market.

1. Prepare all components according to the list and (Figure 1)³⁶ assemble them as follows: acquire a wooden/plastic/metal telescopic or non-telescopic pole with a light telescopic handle, up to 3 m in length, and connect a pruning saw safely and firmly to the pole (Figure 1A; Figure 3A); prepare a container (10-150 mL) with a metal screw plug cap having a custom-drilled 2 mm aperture (inner diameter) for the growth regulator (Figure 1B) and a nozzle with a 2 mm aperture (e.g., stainless steel hollow-through lamp with hole screw).
   NOTE: The commercial off-the-shelf manual pole saw with further installation of the container for the growth regulator might also be used to construct the Mistletoe Eradicator. Light weight facilitates the work at high peripheral branches of the host tree both from the ground and from the tree. The apertures of both screw plug cap and nozzle might vary in between 2-5 mm and define the herbicide dropping speed. The optimal aperture is 2 mm.
2. Firmly connect all metal details with the welding gun in a way that one side of the nozzle (Figure 1B-4) is connected by welding to the metal screw plug cap (Figure 1B-3) tightly fitting the container (Figure 1B-2), while its opposite side is welded to the upper outer corner of the saw blade (Figure 1B-1). Keep a pore (Figure 1B-5) at the point of the attachment of the nozzle and the cutter blade open (Figure 1D).
3. Fill the container with water for the dropping test, close the screw plug cap firmly and twist the pole in working position - the sharp surface of the saw blade downwards, the container upwards and upside down. Ensure that the liquid slowly drops down on the saw blade (Figure 2A (inset), Figure 3C).
4. In case of clogging, clean the 2 mm-wide nozzle using fine needle (e.g., with a syringe needle or a fine sewing needle) until the clog is removed and the herbicide dropping is restored.
5. For transportation or storage, empty the container and secure Mistletoe Eradicator with a saw cover or scabbard.
   CAUTION: Misuse of Mistletoe Eradicator may result in serious or fatal injuries, so the sharp surface of the blade must be covered.

Figure 1: Variants of Mistletoe Eradicator tool. (A-D) An original Indian prototype constructed, tested on walnuts in Kashmir Valley, and patented in India³⁶: (A) the terminal unit of the tool, which needs to be adjusted on the wooden/plastic/metal telescopic or non-telescopic pole with a length up to 3 m; (B) the junction between the pruning saw blade (1) and the container (2) with the drilled metal screw plug cap with 2 mm aperture (3) welded to the nozzle with 2 mm aperture (4) ending with a pore (5); (C) a pore (5) at the point of the joint of the nozzle with the pruning saw blade; (D) the slow dropping of herbicide through the screw plug cap from the container to the nozzle, and from the nozzle to the pruning saw blade through a pore (5); general scheme. (E) and (F) provide details of an alternative version of Mistletoe Eradicator constructed in Ukraine from a commercial tree manual pole saw (s); perforated garden saw with pole handle (p); (b-n) adjustable bolt-nut connection between the screw cap tube (t) with rounded false bottom and the saw blade. Scale bars for (A) is 5 cm and for (B-D, F) is 2 cm. Please click here to view a larger version of this figure.

Figure 2: Mistletoe Eradicator operation mode. (A) from the ground; (B) from the tree by a certified arborist. Please click here to view a larger version of this figure.

Figure 3: A working prototype of Mistletoe Eradicator tested on walnut trees in Kashmir valley in action. (A, B) A demonstrative tool set up without the growth regulators in hands of the operator. (C) The pruning position of Mistletoe Eradicator in relation to V. album exophyte. At the hidden side of the tool the slow release of the growth regulator from the container through the pore at the distal end of the nozzle occurs at the site of pruning. (D) Alternative on-the-tree operation mode and eradication of V. album parasitizing the peripheral host branch. Please click here to view a larger version of this figure.

3. Herbicide preparation

1. Choose local, commercially available analogue of mistletoe growth regulator(s), ethephon (2-Chloroethylphosphonic acid) or glyphosate (N-(Phosphonomethyl)glycine. Check the correspondence of the chosen herbicides to local legislation since ecological permissions and licenses might be necessary.
2. Dilute plant growth regulators according to their specification sheets and manufacturer instructions to prepare stock solutions for short-term storage (not longer than 1-2 days) at 4 °C. On the day of work, prepare 4% -10% working solutions from stock solutions ex tempore.
   NOTE: Treatments with the growth regulators must be performed by certified workers and arborists according to the current legislation in the country of operation.

4. On-site safety rules

1. For all operator(s) and assistant(s) allowed to operate Mistletoe Eradicator from the ground, provide sufficient personal protection (Figure 2A; Figure 4B): nonslip steel toe work boots; liquid-proof, chemical-resistant coverall or a suit with a hood; a helmet; a chemical respirator due to the risk of inhaling herbicide fumes; an eye/face shield/protecting goggles that conforms to ANSI Z87.1 or CE safety standard; chemical-resistant gloves to protect hands from mechanical damage and/or chemical injuries or heavy nonslip gloves for improved grip. In the neighborhood of the operation area, ensure water access is available in case of emergency.
2. Ensure that only licensed arborists with at least one assistant is allowed to operate Mistletoe Eradicator from the tree, using safe gear, bright ropes, arborist lanyards and other professional equipment (Figure 2B). Do not use Mistletoe Eradicator in recreational places. Mark the operation zone and trees with bright stripe tape to prevent the presence of outsiders.

Figure 4: An alternative version of Mistletoe Eradicator tested in Ukraine. (A) Free-hand ground-based pruning of the European mistletoe (Viscum album subsp. album L.) exophyte parasitizing the red buckeye (Aesculus pavia L.) branch in M.M. Gryshko National Botanical Garden, National Academy of Sciences of Ukraine, Kyiv, Ukraine. (B) An arborist with the tool. (C) Close-up of the tool on the tree bifurcation. (D) Pruned exophyte, (E) cable tie (c) and adjustable bolt-nut connection (b-n) between the screw cap tube (t) with rounded false bottom and the perforated garden saw blade (s) saw blade with traces of the demonstrative liquid (prepared using a dry E-160с food color additive) mimicking the growth regulator. (F) V. album exophyte stub treated with the demonstrative liquid. Scale bar is 2 cm. Please click here to view a larger version of this figure.

5. Mistletoe Eradicator operation mode

1. Prune the mistletoe foliage before their fruiting with sticky viscin-covered berries, and after the harvesting of the host trees. Remove the saw cover or scabbard from the tool and check the reliability of the connection between all parts of Mistletoe Eradicator. Do not operate a damaged, improperly adjusted, or not completely or insecurely assembled tool.
   CAUTION: Do not hit rocks, stones, or other foreign objects with the blade of Mistletoe Eradicator. Do not cut solid metal, sheet metal, plastics or any non-wood materials with it.
2. Evaluate the distance from the operator to the targeted mistletoe on the peripheral host branches and adjust the appropriate length of the telescopic stick to get free access to the attachment point of mistletoe with the host tree (Figure 2A). Ensure that there are no obstructions in the way of Mistletoe Eradicator toward the mistletoe on the tree.
3. Find an appropriate saw position (~45° of inclination) in relation to the mistletoe exophyte present in the closest proximity to the host branch/stem (Figure 2A (inset), Figure 3C, Figure 4A).
4. Fill the container up to ¾ of its volume with only one growth regulator in working concentration, close the screw plug cap firmly and place Mistletoe Eradicator in a non-working position - the sharp surface of the saw blade upwards, the container downwards, no liquid dropping (Figure 1A).
5. Stand closer to the tree and place the tool in the working position by twisting the pole (Figure 2A, inset). Operate Mistletoe Eradicator with both hands while maintaining a safe distance from the assistant(s) and any bystanders (Figure 2A).
6. Ensure a good firm grip on the tool and prune an exophyte with short sawing movements of the cutting blade (Figure 4A). Ensure that the distal end of the saw blade does not touch the neighboring host branches and/or stem which might damage them and the container.
7. Add more growth regulator as it gets exhausted. The amount of herbicide for one V. album stub varies between 1-5 mL depending on the nozzle diameter.
8. After the pruning of one mistletoe exophyte, place the Mistletoe Eradicator in non-working position and let the air come inside the container through the pore. Relocate to another mistletoe exophyte, place Mistletoe Eradicator in working position and repeat the procedure.
   NOTE: If the Mistletoe Eradicator is operated from the tree by a trained arborist (Figure 2B), the rules for high-altitude work in the country of operation must be followed.

6. Mistletoe foliage piling and finishing

1. Pile the pruned exophytes between the host trees. Mistletoe pruned using Mistletoe Eradicator cannot be collected for pharmacological, ritual, or forage purposes because of the potential danger posed by the growth regulators to human and animal health.
2. Dispose the growth regulators following manufacturer instructions and local environmental regulations.
3. Clean the tool mechanically after work, empty and thoroughly wash the container with tap water and dry it. Discard the disposable protective gloves and respirators in special containers. Thoroughly rinse the reusable cloth, boots, helmets, and eye protection with tap water, dry, and store separately.
4. Protect the sharp part of the Mistletoe Eradicator with a saw cover or scabbard.

Representative Results

Different V. album management approaches were tested in Kashmir (India) in walnut plantations during 2012-2016 before the use of the Mistletoe Eradicator, such as targeted foliar spraying with glyphosate and ethephon in different concentrations, pruning/clipping of mistletoe exophytes, secure covering of the wound with polyethylene wrap and application of the same herbicides to the cut ends of 2-3 cm-long mistletoe stubs.

Each approach was tested on five V. album exophytes on five individual trees (n = 25 in total), and observations on V. album mortality were recorded regularly starting from 15 days after the treatment to up to 9 months. It was found that the efficiency of V. album chemical control by using just the growth regulators without pruning was low (Table 1). Thus, after the spot spraying of 3%-5% glyphosate and 3%-5% ethephon, only 1%-6% of V. album exophytes lost fruits, leaves, and terminal branches.

Treatment	Rate of mistletoe mortality (%)
water (mock control)	0
3% glyphosate	1
4% glyphosate	1
5% glyphosate	5
3% ethephon	2
4% ethephon	6
5% ethephon	6

Table 1: Effect of spot spraying of growth regulators on the exophytes of the European mistletoe (Viscum album subsp. album L.) parasitizing walnuts.

Next, pruning/clipping of V. album exophytes followed by polyethylene wrapping of the host branch caused maceration of the host tissues as a result of moisture accumulation (Figure 5F).

Figure 5: Mistletoe chemical and mechanical control on walnuts in Kashmir Valley. After treatment with (A) 5% glyphosate; (B) 10% glyphosate; (C) 10% ethephon; (D) 20% ethephon; (E) water (mock control), the mistletoe resprouting was monitored. (F) Maceration of the host tissues at the branch wrapped with polyethylene for 90 days as a result of moisture accumulation. Observations were done 9 months after pruning and treating the mistletoe stubs with the growth regulators. Please click here to view a larger version of this figure.

However, as compared to just pruning, after which 98% of exophytes resprouted within 9 months, mistletoe regrowth on polyethylene-wrapped host branches was low (~9%; Table 2).

Treatment	Mistletoe resprouting after 9 months (%)	Angular (Arc Sin) transformation
pruning only (control)	98	82.73
pruning + polyethylene bandage	9	17.43
pruning + 1% glyphosate	39	38.86
pruning + 2% glyphosate	35	36.21
pruning + 5% glyphosate	33	35.03
pruning + 10% glyphosate	7	15.27
pruning + 1% ethephon	37	37.44
pruning + 2% ethephon	20	26.46
pruning + 5% ethephon	9	17.43
pruning + 10% ethephon	2	6.23
pruning + 20% ethephon	0	0

Table 2: Effect of spot spraying of growth regulators and polyethylene bandaging on the pruned exophyte stubs of the European mistletoe (Viscum album subsp. album L.) parasitizing walnuts.

In turn, the combination of exophyte pruning to 2-3 cm stubs along with application of 5% and 10% ethephon to cut end of mistletoe stubs with a fine brush resulted in only 9% and 2% of V. album resprouting. This inspired the development of Mistletoe Eradicator, which can perform mechanical and chemical control of mistletoe growth simultaneously (Figure 1, Figure 2, Figure 3, Figure 4, Figure 5). Its efficiency was tested after patenting³⁶ in the Kashmir Valley on walnut trees heavily infested with V. album (Figure 4). The pruning of V. album exophytes was done with Mistletoe Eradicator loaded with 10% ethephon, 10% glyphosate, or distilled water (mock control) on 15 exophytes (for each treatment) on 6 walnut trees (total n = 270). Statistical analysis of all datasets was performed using a statistical analysis software³⁷. All datasets were first subjected to the Shapiro-Wilk test to test the normality, and then to data transformation using angular (arc sine) transformation technique for data expressed as decimal fractions or percentages³⁸. After that the transformed data were analyzed with two-way analysis of variance (ANOVA) test, and CD_0.05 (critical difference) was calculated to compare the pairs of treatments. This study was started in November 2017 and the observations on regrowth/resprouting of mistletoe from the cut ends were recorded in July-August 2018. It was found that the V. album 2-4 cm-long stubs treated with 10% glyphosate or 10%-20% ethephon on the cut end using the Mistletoe Eradicator had very low resprouting, 6% and 5%, respectively, as compared to mock control (97%; Figure 5, Table 3).

Treatment	Mistletoe resprouting after 9 months (%)	Angular (Arc Sin) transformation	Efficiency (%)
10% ethephon	5.2	13.44	95.05
10% glyphosate	6.2	14.28	93.58
water (mock control)	96.66	79.96	―

Table 3: Effect of the synergic action of Mistletoe Eradicator tool and growth regulators on the European mistletoe (Viscum album) parasitizing walnuts.

Thus, after the treatment with 10% ethephon only 5 out of 90 pruned exophytes resprouted after 9 months of observation, after treatment with 10% glyphosate only 6 out of 90 exophytes resprouted, and after the treatment with water (control) 87 out of 90 exophytes resprouted. Therefore, the data indicates that Mistletoe Eradicator loaded with 10% ethephon or 10% glyphosate is an efficient tool for V. album management reaching almost to 95% efficiency in controlling mistletoe regrowth.

After the field trials, the Mistletoe Eradicator was successfully implemented by walnut growers in KVK, Budgam (India) in 2019-2022 using 10% ethephon and rarely 10% glyphosate for the efficient control of mistletoe reporting an abscission of 96%-98% of V. album exophytes.

Alternatively, a modified version of Mistletoe Eradicator was constructed in Ukraine to show that this tool can be easily designed from off-the-shelf components found in open market, and inspire the potential users to customize it, for example, with 3D-printed components. It consists of the commercial tree manual pole with perforated garden saw and screw cap tube with rounded false bottom with a 1-2 mm pore for the growth regulator, adjusted with bolt-nut connection between its bottom and one of the perforations of the saw blade and anchored with cable ties (Figure 1E, F; Figure 4E). The Ukrainian version of Mistletoe Eradicator was tested at the closed research and monitoring zone of M.M. Gryshko National Botanical Garden of National Academy of Sciences of Ukraine (Kyiv, Ukraine) with the use of demonstrative liquid (a dry E-160с food color additive) to track its dropping and test the covering of the mistletoe stub surface (Figure 4A-D,F). The volume of the liquid varies in between 1-5 mL depending on the diameter or the mistletoe stub and accuracy of the saw cut.

Discussion

Mistletoes cannot be treated exclusively as pests, since many of them play a crucial role in the ecosystem as biodiversity hotspots and connecting tropical and topical hubs for multiple organisms, behaving more like epiphytes than parasites with negligible negative consequences for their hosts^6,8. Therefore, the measures aimed to control their spread have to be highly selective and based on the understanding of both biology and biotic associations of definite mistletoe species. The initial step of the multilevel strategy for mistletoe control in natural ecosystems must include surveys and evaluation of the severity of mistletoe infestation using many approaches, for example, 6-class dwarf mistletoe rating (DMR)²⁰ and modified dwarf mistletoe rating (MDMR)³⁹, or ROFAD grading, where R stands for rare (up to 5% of mistletoe colonization of the photosynthesizing parts of the host trees), O for occasional (6%-10%), F for frequent (11%-30%), A for abundant (31%-50%), and D for dominant (more than 50%)³². It is recommended to adapt these scales to mistletoe species, and agree on its minimum infestation rate, which requires the control program execution, when the eradication is needed to prevent its further self-dissemination, e.g., use of Arceuthobium seed ballistic leads to its spread due to the increased hydrostatic pressure and thermogenesis inside⁴⁰ or dispersal with the help of vectors, e.g., birds⁴¹. After the evaluation of mistletoe infestation severity, the inspection of the presence of bird nests has to be done and, in case they are revealed, all works in the close proximity to the nesting sites must be stopped or at least substantially limited. Besides the evaluation of the degree of mistletoe infestation, other important parameters such as the absence of long-term biotic interactions with birds, insects, reptiles, mammals, and other animals, speed of dissemination, host-specificity, cultural importance for local human communities, and economic damage have to be considered prior the decision of its eradication. Moreover, in frames of the selective mechanical mistletoe eradication, both photosynthesizing and endophytic parts of V. album subsp. album can be utilized for medicinal (e.g., for lectins and viscotoxins extraction), decorative (seasonal winter holidays in Europe, jewelry, and dishware from wood rose haustoria, and others), gastronomic (e.g., for the preparation of the pomace brandy-based Croatian liquor biska), and forage purposes⁷. The green mass of mistletoe exophytes might be reused as mulch, chopped in situ and composted under the host trees, which will retain all nutrients within the stand⁷.

The data regarding the higher efficiency of jointed mechanical and chemical mistletoe control corroborates the results of Lichter et al.³³ showing that the regrowth of leafy mistletoe (Phoradendron macrophyllum (Engelm.) Cockerell) parasitizing Modesto ash (Fraxinus velutina Torr.) from buds or from the endophytic system was significantly limited after the spraying of mistletoe cut stubs with 2% ethephon as compared to pruned or sprayed only, after which the regrowth of the mistletoe occurred in the same season. Moreover, ethephon was the most efficient dwarf and leafy mistletoe control agent when sprayed onto cut mistletoe stubs³⁴. It might be assumed that the mistletoe pruning followed by spraying with growth regulators suppress further endophyte development.

One of the benefits of Mistletoe Eradicator is that there is no need to repeat it annually as compared to foliar sprays, which need to be done on a regular basis during the fall season. Next, the targeted use of herbicides being slowly released from the container of the Mistletoe Eradicator allows to reduce the volume required for an efficient mistletoe chemical control avoiding side-spraying.

Limitations of the Mistletoe Eradicator tool concern mostly the scale of its use, because for the efficient eradication of V. album in walnut plantations in Kashmir many trained operators were involved. Furthermore, the physical fitness and health conditions of the operators are important because the work with the Mistletoe Eradicator is time-consuming and tense.

The most critical steps in the protocol are the respect for safety rules, the use of glyphosate and ethephon following the regulations of the country and in accordance with the environmental laws, the choice of proper phenological phase of the host tree and monitoring of the weather. First, the operation of the Mistletoe Eradicator and treatment of the host trees parasitized by mistletoes in orchards, monoculture stands, plantations, parks, green spaces, windbreaks, gallery forests and other artificial and/or natural tree associations, requires permission from the relevant tree care authorities and/or owners. Systemic herbicides have to be used with extra caution, since they are potentially harmful to environment on a long-term basis and might affect host trees^21,34.

The most frequent mistakes during the work with Mistletoe Eradicator as detailed here should be avoided:

Neglecting safety precautions: The lack or misuse of protective googles, safety gear, cap, wrong fixation of the climbing gear on the tree, etc. are dangerous.

The use of Mistletoe Eradicator during the vegetation season of the host trees: The optimal time for mistletoe pruning and herbicide treatment has to be adjusted according to the phenological phase of host trees, which must be without fruits, leaves and actively developing buds.

Unfavorable weather conditions: Mistletoe Eradicator is recommended to be operated under dry weather, since precipitations such as rain or snow can wash away the growth regulators⁴² and/or reduce their biological activity. However, it was shown under laboratory conditions that leafy mistletoe absorbs ethephon within ~1 h after the spraying⁴³. Moreover, wind force and direction have to be considered as well, since they can affect the stability of both the tool and the operator, and also blow off the drops of herbicide, which can cause irritation of the skin or eyes. Therefore, monitoring of weather forecast (wind direction and strength, temperature, probability of rain, snowing, fog, or frost) with a reliable meteorological service is highly desirable.

Loss of balance: The position of the operator on the ground, on the aerial platform or on the tree during the work with Mistletoe Eradicator must be stable.

Detachment of the saw from the handle: Mistletoe Eradicator handle should be fixed properly to wooden/plastic/metal bar and double-checked to avoid loose fitting.

Herbicide leakage during the relocation of the operator to another site: After cutting one exophyte, the tool must be inverted to keep the container in upward position until the operator reaches the next mistletoe exophyte, to prevent unnecessary herbicide loss. Furthermore, the container is recommended to be closed tightly to prevent leakage from the loosely fitted screw plug during the occasional inverting of the Mistletoe Eradicator.

Nozzle clogging: Prevent dirt or any particulate material from getting into the container to avoid nozzle clogging. Prior to Mistletoe Eradicator use, the operator has to check the presence of unhindered herbicide dropping from the container to the saw blade. In case of clogging, the 2 mm-wide nozzle can be cleaned using fine needle (e.g., with a syringe needle or a fine sewing needle) until the clog is removed and the herbicide dropping is restored.

Damage to the container: Operate Mistletoe Eradicator carefully and do not hit stones, tree trunks, concrete walls, and other foreign objects, to prevent the breakage of the fragile nozzle as it is the weakest link in the chain.

In frame of an integrated pest management^7,30, not only plant growth regulators can be used in the container of Mistletoe Eradicator, but also suspension of spores of V. album biocontrol agents like Phaeobotryosphaeria visci (Kalchbr.) A.J.L. Phillips & Crous, Alternaria alternata (Fr.) Keissl., and Sarocladium (= Acremonium) kiliense (Grütz) Summerb. can be used⁴.

In conclusion, this easy-to-handle tool allows to reduce the effort and time for mistletoe control, since it performs exophyte pruning and chemical treatment simultaneously as compared to the sequential procedures. The improvement of the prototype of Mistletoe Eradicator by users is highly welcome as well as its testing in different biotopes on different mistletoe species.

Materials

Name	Company	Catalog Number	Comments
Components of Indian Mistletoe Eradicator*
Bosch 2607010538 HSS-G Drill Bit Set, Silver	Bosch	2607010538	https://www.amazon.co.uk/Bosch-Professional-2607010538-HSS-G-Silver/dp/B001IBMPL2
Container- Aluminium Bottle- with screw plug Cap	Suparna Exports, Pvt. LTD	n/a	http://www.aluminumbottlecans.com/aluminum-bottles-with-screw-plugs.php
Drill GSR12V-300HXB22	Bosch	GSR12V-300HXB22	https://www.boschtools.com/us/en/boschtools-ocs/cordless-screwdrivers-gsr12v-300hxb22-207019-p/
Genuine C04AL-1487425 engine valve guide for engine spare parts	Shangchai	C04AL-1487425	https://www.alibaba.com/product-detail/Genuine-C04AL-1487425-engine-valve-guide_60704258097.html?spm=a2700.details.0.0.2cfb6b8b2k JBOB
HBCHEN Handheld Welder Gun Portable Welding Machine, 220V Small Welding Machine and 110V Arc Welder	HBCHEN	YB320	https://www.amazon.com/HBCHEN-Handheld-Portable-Eliminate-Experience/dp/B097BWBCMB
The nozzle: stainless steel outer bolt hollow-through lamp with hole screw	n/a	M6M8M10M12	https://www.aliexpress.com/item/32950601820.html?spm=a2g0o.seo_rank.0.0.62642d1 fLzjNFL
The pruning saw blade	Lee Valley	09A0356	https://www.leevalley.com/en-us/shop/garden/garden-care/saws/76626-pruning-saw-blade?item=09A0356
Components of an alternative Ukrainian Mistletoe Eradicator*
Aluminium Telescopic Hand Gardena Combisystem 160-290 cm	ROZETKA	Code 03720-20	https://rozetka.com.ua/202484293/p202484293/characteristics/
Amazon Basics Multi-Purpose Cable Ties - 4-Inch/100mm	Amazon Basics	n/a	https://www.amazon.com/AmazonBasics-Multi-Purpose-Cable-Ties-200-Piece/dp/B087MKMSDY/ref=sr_1_1_sspa?crid=3FEZFXGOR4VPC&keywords =cable%2Bties&qid=1642924567&sprefix =Cable%2Btie%2Caps%2C162&sr=8-1-spons&spLa=ZW5jcnlwdGVkUXVh bGlmaWVyPUEyTU9QMEo2WUp YMjBLJmVuY3J5cHRlZElkPUEwM jYzMDkxQUtWODVWU00xU0ZYJ mVuY3J5cHRlZEFkSWQ9QTA1O Tc2NjUyVzdHV0E4UUZOWkU1Jn dpZGdldE5hbWU9c3BfYXRmJmF jdGlvbj1jbGlja1JlZGlyZWN0JmRv Tm90TG9nQ2xpY2s9dHJ1ZQ&th= 1
Garden saw GARTNER 540/360 mm with bar handle	Gärtner	Code 80001003	https://gartner-tools.com/ru/product/pila-sadovaja-540-360-mm-s-rukojatkoj-pod-shtangu-gartner/
Loppers INTERTOOL HT-3111	ROZETKA	Code  263723496	https://rozetka.com.ua/intertool_ht_3111/p263723496/characteristics/
M4 / 4mm DOOR HANDLE SCREWS BOLTS 20-22 mm	Boltworld	n/a	https://boltworld.co.uk/collections/m4-bolts/products/m4-4mm-door-handle-screws-bolts-9mm-50mm-lengths-cupboard-door-drawer-knob?variant=15820185469021
M4 Hexagon Weld Nut A4 Stainless Nut DIN 929	Boltworld	n/a	https://boltworld.co.uk/products/m4-hexagon-weld-nut-a4-stainless-nut-din-929?_pos=1&_sid=a8a2c15c9&_ss=r& variant=32145946706013
Sarstedt 5ml Screw Cap Tube with Rounded False Bottom and Cap Assembled, with Print, 92x15.3, PP	Sarstedt	n/a	https://www.amazon.com/Sarstedt-Rounded-Bottom-Assembled-92x15-3/dp/B07GXZ51BN
Chemicals
Ammonium salt of Glyphosate 71% SG EXCEL MERA 71	Excel Crop Care	n/a	http://www.excelcropcare.com/product/domestic/crop-protection/herbicides/excel-mera-71.php
E-160c*	EUROIMPEX	n/a	https://euroimpex.net.ua/ru/krasiteli/
Ethephon (“Promoter”)	Fil, India Ltd	n/a	https://www.filindustries.com/our-businesses.php
Protection*
Gloves Tegera Cut Control	EJENDALS	TEGERA 9121	https://www.ejendals.com/globalassets/inriver/resources/9121_productsheet_en. pdf
Helmet CAMP Rockstar	CAMP	ID: 0202	https://www.camp-usa.com/outdoor/product/helmets/rock-star-helmet/
Mesh visor Stihl	STIHL	n/a	https://www.stihl.co.uk/STIHL-Products/Personal-protective-equipment/Face-and-ear-protection/22184-1545/Face-hearing-protection-nylon-mesh.aspx
SAS/STAT	SAS Institute Inc. 2013, USA		statistical analysis software
*materials and equipment marked with asterisks are changeable and can be modified and adjusted basing on the country of the use and avaliability of the components in the market. Moreover, Mistletoe Eradicator can be custom-tailored by the professional welding engineer.