Elsevier

Crop Protection

Volume 141, March 2021, 105467
Crop Protection

Use of acibenzolar-S-methyl and other novel products for the management of Aphelenchoides fragariae on ornamental plants in glasshouse and commercial conditions

https://doi.org/10.1016/j.cropro.2020.105467Get rights and content

Highlights

  • Use of elicitor of plant defences Acibenzolar-S-methyl (ASM) against foliar nematodes.

  • Multiplication of Aphelenchoides fragariae was reduced by novel products.

  • Spirotetramat, abamectin, azadirachtin & ASM reduce multiplication of A. fragariae.

  • Leaf wetness before treatment increased product's efficacy against A. fragariae.

Abstract

Several chemical, biopesticide and elicitor treatments were evaluated on healthy plants inoculated with leaf and bud nematodes (Aphelenchoides fragariae). Aphelenchoides fragariae is a major threat to ornamental plant production worldwide, and its management poses a great challenge due to its wide host range of herbaceous, ferns and woody plants. Commercially available products containing spirotetramat, abamectin, azadirachtin and the elicitor of plant defences, acibenzolar-S-methyl (ASM), were assessed for their ability to reduce the multiplication of A. fragariae inoculated on two plant species: Anemone hupenhensis (Japanese anemone), and Buddleja davidii (Buddleja).

Treatments were applied individually and in combination with ASM in a spray programme. All treatments consistently showed a significant reduction of nematode multiplication in treated plants compared to the control. Programmes of ASM with spirotetramat, abamectin or azadirachtin had significantly lower nematode populations on both plant species compared to the untreated plants. In Buddleja plants, a programme using spirotetramat + ASM had a 97% reduction of the A. fragariae population over the control (ROC) while ASM, spirotetramat, abamectin, azadirachtin, ASM + abamectin and ASM + azadirachtin caused between 78 and 94% ROC. On Japanese anemone, the highest nematode ROC (95%) was obtained with the spirotetramat + ASM programme, while other treatments (ASM, spirotetramat, abamectin, azadirachtin, ASM + abamectin and ASM + azadirachtin) had a range of 80–94% reduction of A. fragariae over the control.

Management of plants infested by leaf and bud nematodes may prove challenging; however, all the treatments investigated demonstrated a significant reduction in nematode population in Buddleja and Japanese anemone, indicating that they have significant potential as effective alternatives to manage A. fragariae in ornamental plants. The potential of ASM alone or in programmes with other actives is discussed in relation to their use in the management of A. fragariae.

Introduction

Leaf and bud nematodes ‘LBN’ (Aphelenchoides spp. including A. besseyi, A. fragariae and A. ritzemabosi) are microscopic roundworms that live in leaf and tissue and cause significant injury to numerous ornamental plant species (Kohl et al., 2010; Sánchez-Monge et al., 2015). The range of symptoms exhibited by foliar nematodes varies considerably on flowering ornamentals depending on the host plant. LBN may cause lesions in crops such as Hosta and Salvia, or bronzing and discoloration in crops such as Begonia, Buddleja, Weigela and Japanese anemone (Jagdale and Grewal, 2002; Sánchez-Monge et al., 2015).

When leaves are infested by LBN, they become chlorotic and subsequently turn necrotic; such plants often become unsaleable causing significant economic losses to growers (Kohl et al., 2010). The control of LBN on hardy ornamental plants can be challenging because of the survival strategies of the pest and its ability to survive ecto- and endo-parasitically.

(De-Waele, 2002). Due to pesticide regulation and environmental concerns, many previously available nematicides approved for use for LBN management are no longer available to growers. Chemical treatments such as aldicarb, diazinon, parathion and oxamyl have been used in the past for effective control of foliar nematodes (LaMondia, 1999; Jagdale and Grewal, 2002; An et al., 2017). However, most of these chemicals are no longer available due to commercial withdrawal, government regulations and environmental concerns, thus chemicals are limited in availability and efficacy which has affected the nursery industry (LaMondia, 1999; Jagdale and Grewal, 2002; An et al., 2017). Although some insecticides such as abamectin have been demonstrated to be effective against foliar nematodes on some ornamentals (LaMondia, 1999; Young and Maher, 2000), they are not registered as a nematicide for use in the UK. Consequently, there is an urgent need to identify alternative approaches for the management of LBN.

Plants are able to actively defend themselves or induce self-resistance towards virulent pathogens such as nematodes and fungi (Walters et al., 2014). The treatment of plants against pathogens with various agents including synthetic chemicals, may lead to induced resistance such as systemic acquired resistance (SAR), to attack by pathogens both locally and systemically within plants (Walters et al., 2005). Resistance to pathogens can be induced chemically in plants (Kessmann et al., 1994; Malamy et al., 1996; Ward et al., 1991) when compounds which can mimic the action of salicylic acid (SA), such as acibenzolar-S-methyl (ASM) are applied to plants (Oostendorp et al., 2001). There have been no reported studies on the induction of resistance against LBN on ornamental plants. Most of the available investigations of induced resistance against nematodes have focussed on root knot nematodes (Meloidogyne incognita, M. javanica, M. chitwoodi) in tomato plants (Oka et al., 1999; Cooper et al., 2005) and a few studies on M. chitwoodi and Pratylenchus spp. on potato plants (Collins et al., 2006; Dos-Santos et al., 2013). Molinari and Baser (2010) reported a significant reduction in the reproduction of root-knot nematode (M. incognita) on tomato roots (Solanum lycopersicum) with improved plant growth due to root-dip and soil drench applications of ASM. ASM has been commercially available in Europe as Bion® and Inssimo®, and Actigard® in the USA (Walters et al., 2005), and has been primarily used for white rust (Puccinia horiana) management on Chrysanthemums.

Past research work has indicated that some currently available insecticides such as abamectin and spirotetramat have nematicidal potential, and may be useful for the management of A. fragariae (LaMondia, 1999; Rotifa and Evans, 2016). Bennison et al. (2018) confirmed the potential of both spirotetramat and abamectin to control A. fragariae by significantly reducing nematode multiplication in the leaves. This result also confirmed reports by LaMondia (1999) and Young and Maher (2000) on abamectin use against leaf and bud nematodes (A. fragariae and A. ritzemabosi).

Products and extracts derived from neem (Azadirachta indica) have demonstrated suppression of populations of root knot nematodes (M. incognita (Lynn et al., 2010)), potato cyst nematode (Globodera rostochiensis) and free living nematodes on potato (Akhtar and Alam, 1991). Leaf-disc assays demonstrated that Neem oil caused 36 and 90% mortality in a 20 and 2-fold dilution respectively, to A. fragariae within 24–72 h of exposure (An et al., 2017).

In the search for effective products against LBN under field conditions with particular focus on A. fragariae, two experiments in commercial nurseries and one glasshouse study were conducted to investigate the efficacy of products that could limit multiplication of nematodes on nematode-free plants that were inoculated with nematodes 4 days post-first treatment, to determine whether plants remain symptom-free and have limited nematode multiplication within the leaves.

The objectives of this study were to determine the efficacy of the foliar insecticides spirotetramat and abamectin, a neem plant extract product (azadirachtin), and a synthetic chemical elicitor (ASM), as individual treatments, and in combination with ASM, for the management of A. fragariae on nematode-inoculated ornamental plants.

Section snippets

Plants and nematodes

Trial 1 used certified nematode-free Japanese anemone (Anemone x hybrida ‘Honorine Jobert’) at a commercial ornamental nursery in Oxfordshire, UK. The prevailing average temperature was 11.9 °C of 07:38 h - 11:41 h night length and 23.5 °C for 12:19 h - 16:22 h day length during the duration of the trial.

Buddleja davidii ‘White Profusion’ plants were used in Trial 2 at a commercial nursery in Herefordshire, UK. Plants were kept in a covered glasshouse facility isolated from other plants, with

Trial 1: Anemone x hybrida ‘Honorine Jobert’

There was a significant (P < 0.05) difference in the final nematode population between all the treatments and the untreated Control (Table 2).

The mean values obtained for nematode population in the Japanese anemone leaves ranged between 157 and 2570 per g-1 of leaf (Table 2). The spirotetramat + ASM treatment had the lowest mean population (157.8) while the untreated control gave the highest mean nematode population of 2570.2 (Table 2).

In all the treatments, the nematode population was

Discussion

Results from trials at three locations have identified products, which could play a significant role in the preventative management of LBN infestation on ornamental plants by reducing the appearance of symptoms of nematode infestation through reduction of nematode multiplication in plants (summarised in Table 5). Some of these products can also be used in a curative role by reducing nematode multiplication within already infested plants (Rotifa and Evans, in prep.). Foliar application of these

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

The authors are grateful to Agriculture and Horticulture Development Board (AHDB) for the financial assistance to carry out this study. In addition, much appreciation to the two commercial nurseries in England and SRUC Edinburgh which provided locations for the trial sites.

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