Plutella xylostella can become
resistant to many insecticides.
(Photo: Clemson University,
www.insectimages.org)
Diamondback moth resistance management and prevention strategy
(Revised October 2004)
Reasons for strategy and update
Diamondback moth, Plutella xylostella, is capable of becoming resistant to a wide range of insecticides. Management strategies aimed at preventing or minimising resistance will help maintain control and conserve the effectiveness of existing products. This is an update of an earlier resistance management strategy (Cameron 1996).
Background
Diamondback moth is frequently a pest of vegetable brassicas, especially in areas with long, warm summers. Brassicas grown for forage are also affected, but considerable damage can be tolerated in these crops, and insecticide treatment is rarely justified for control of diamondback moth. However, insecticides are used to control other insects and these may affect diamondback moth. Other host plants include turnip, swede and cruciferous weeds, such as wild mustard and radish.
Insecticide resistance associated with crop failures in neighbouring countries has been reported in Australia (Endersby & Ridland 1994) and the Cook Islands (M.G. Hill, pers. comm.). Resistance in South-East Asia, Japan, USA and Central America has been summarised by Sun (1992) and includes resistance to Bacillus thuringiensis and insect growth regulators.
Two other closely related species, Plutella antiphona and Rhigognostis sera, occur on crucifers in New Zealand (Dugdale 1973), but these species are rare on vegetable brassicas (Beck 1991).
Products with label claims for diamondback moth control in New Zealand
| Pesticide category and IRAC chemical group | Pesticide common and (product) names | Type of label claim for each crop | ||
|---|---|---|---|---|
| Forage brassicas | Vegetable brassicas | Vegetables | ||
| Carbamate 1A | carbaryl (Carbaryl, Sevin) | caterpillars | ||
| Organophosphate 1B | acephate (Lancer, Orthene) | DBM | ||
| diazinon (Basudin, Dew, Diazinon, Diazinyl) | DBM | caterpillars | caterpillars | |
| dichlorvos (Nuvos) | caterpillars | caterpillars | ||
| maldison (Malathion, Maldison) | DBM | DBM | ||
| methamidophos (Metafort, Monitor, Tamaron) | DBM | |||
| parathion methyl (Folidol) | caterpillars | |||
| trichlorfon (Trifon) | DBM | DBM | ||
| Organoposphate/synthetic pyethroid 1B/3 | permethrin/pirimiphos-methyl (Attack) | DBM | ||
| trichlorfon/cypermthrin (Partna) | DBM | |||
| Cyclodiene 2A | endosulfan (Flavylan, Thiodan) | DBM | ||
| Phenylpyrazole 2B | fipronil (Ascend) | DBM | ||
| Pyrethrins 3 | pyrethrum (Garlic & Pyrethrum) | caterpillars | ||
| Synthetic pyrethroid 3 | alphacypermethrin (Dominex, Fastac) | DBM | ||
| bifenthrin (Talstar) | DBM | |||
| cyfluthrin (Baythroid 5 EC) | DBM | |||
| cypermethrin (Ripcord) | DBM | |||
| deltamethrin (Decis Forte, Deltaphar 25EC) | DBM | DBM | ||
| esfenvalerate (Sumi-alpha) | DBM | |||
| lambda-cyhalothrin (Karate Zeon) | DBM | DBM | ||
| taufluvalinate (Mavrik) | DBM | |||
| Spinosyns 5 | spinosad (Success Naturalyte) | DBM | ||
| Bta 11B1 | Bacillus thuringiensis aizawai (XenTari WG) | DBM | ||
| Btk 11B2 | Bacillus thuringiensis kurstaki (Defin WG, Dipel DF, Dipel ES, MVP*II) | DBM | ||
| Bta & Btk 11B1 & 11B2 | Btk and Btk mixture (Agree WDG) | DBM | ||
| Oxadiazine 21 | indoxacarb (Steward) | DBM | ||
Current status of diamondback moth resistance in New Zealand
Extensive and regular use of insecticide against insect pests on vegetable brassicas has led to detectable resistance to several insecticide groups (Bell & Fenemore 1990), and this has recently been associated with control failures. Resistance surveys undertaken over two years (1999 and 2000) in four regions (Pukekohe, Gisborne, Hawke's Bay and Canterbury) show that resistance to synthetic pyrethroids is variable, both between and within regions (Walker et al. 2004). Populations tested from Pukekohe and Hawke's Bay had levels of resistance that may be associated with control failures in the field. Pukekohe populations collected within 4 km of each other had resistance ratios varying from 3.7 to 29.2, demonstrating localised differences in diamondback populations.
Resistance to methamidophos, the standard organophosphate insecticide, appears to be relatively stable with a maximum of 4.4 fold resistance (Walker et al. 2004). There was no significant tolerance to a standard Btk (Dipel 2X) and resistance ratios for 11 field populations ranged from 0.88 to 6.4 fold for the carbamate, methomyl (G.P. Walker & N.A. Berry, unpubl. data). More recent studies have shown no significant resistance in field populations to spinosad, indoxacarb and fipronil (G.P. Walker, unpubl. data).
Resistance management and prevention strategy
The general strategy is to maximise non-insecticidal controls and reduce selection pressure by applying insecticides only when necessary, and by rotating insecticide use between chemical groups in a planned programme.
Note: Control failure does not always imply resistance.
The following guidelines are recommended:
- Use clean transplants to avoid early infestations. Spray in the nursery if necessary. Grow seedlings away from brassica field plantings.
- Destroy cruciferous weeds such as wild radish and mustard to remove sources of infestation. Do not spray these weeds with insecticide.
- Monitor plants at least weekly to detect infestations. Use the action thresholds for caterpillar and aphid pests developed in the Crop & Food Research IPM programme (Berry 2000).
- Comply with label rates and use correct application procedures. Calibrate sprayers at least once a season.
- Use insecticides in accordance with the diamondback moth insecticide rotation strategy (Table 2).
- Plough in crop residues to bury larvae and pupae remaining immediately after harvest.
Research strategies should include ongoing monitoring of resistance to all groups of insecticides used for control of diamondback moth so that growers and consultants can be provided with up-to-date information about effective insecticides.
| Early window September - late January | Late window February - August |
|---|---|
| Apply insecticides only in response to scouting thresholds | |
| Btk1 | Bta1 and mixture of Bta & Btk1 |
| spinosad (Success Naturalyte) | indoxacarb (Steward) |
| fipronil (Ascend) | |
| organophosphates | |
| synthetic pyrethroids | |
| endosulfan | |
| pirimicarb (aphids) | |
1Apply Bt to small larvae on small plants.
Implementation
- Growers should monitor plants to ensure insecticides are applied only when necessary.
- Growers should rotate insecticide groups in accordance with the national rotation strategy.
- Insecticides with label claims for use on brassicas should carry
the following label statement:
IMPORTANT - RESISTANCE MANAGEMENT
Resistance to this pesticide could develop from excessive use. To minimise this risk, use strictly in accordance with label instructions. Avoid using this pesticide exclusively all season, and avoid unnecessary spraying. Maintain good cultural control practices.
References
Beck NG 1991. Lepidopterous pests on vegetable brassicas in New Zealand. PhD thesis, Auckland University, New Zealand. 148 p.
Beck NG, Herman TBG, Cameron PJ 1992. Scouting for lepidopteran pests in commercial cabbage fields. Proceedings of the 45th New Zealand Plant Protection Conference: 31-34.
Bell PD, Fenemore PG 1990. Insecticide resistance in diamondback moth in New Zealand. Proceedings of the 43rd New Zealand Plant Protection Conference: 31-34.
Berry NA 2000. Integrated pest management for brassicas. Crop & Food Research IPM manual, no. 11. Crop & Food Research, Private Bag 4704, Christchurch, New Zealand.
Cameron PJ 1996. Diamondback moth resistance management strategy. In: Bourdot GW, Suckling DM ed. Pesticide Resistance: Prevention and Management. New Zealand Plant Protection Society, Lincoln, New Zealand. Pp. 204-206.
Dugdale JS 1973. The genus Plutella (Hyponomeutidae) in New Zealand and the position of the Cicoxena (Lepidoptera). New Zealand Journal of Science 16: 1009-1023.
Endersby N, Ridland P 1994. Insecticide resistance in Victorian populations of diamondback moth, Plutella xylostella (L.). Australian Entomological Society Conference, Abstract, 31.
Sun C-N 1992. Insecticide resistance in diamondback moth. In: Talekar NS ed. Diamondback moth and other crucifera pests. Proceedings of the 2nd International Workshop, Taiwan, December 1990, AVRDC publication. Pp. 419-426.
Walker GP, Cameron PJ, Berry NA 2004. Implementing an IPM programme for vegetable brassicas in New Zealand. In: The management of diamondback moth and other crucifer pests: Proceedings of the Fourth International Workshop, Melbourne, Australia, 26-29 November 2001. Pp. 365-370.
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