NZPPS pesticide resistance management strategy

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Tomato potato psyllid insecticide resistance management strategy (for potatoes)

Adult tomato potato psyllid,
Bactericera cockerelli (Hemiptera: Triozidae),
with moulted skin of nymph and yellow
eggs on stalks. © Plant & Food Research

Herman TJB & Walker GP (updated Dec24)

Reasons for strategy and update

Tomato potato psyllid (TPP), Bactericera cockerelli, populations are capable of becoming resistant to a wide range of insecticides through repeated use of the same mode of action (MoA) insecticide. It is always better to prevent resistance from developing than to deal with resistance once it has occurred. The cost of TPP resistance to New Zealand could be very significant, and this strategy is designed to reduce selection pressure for resistance as far as possible without jeopardising the quality of produce and export crops.

Potato crops are also subject to potato tuber moth and aphid pest pressure. Cross over of insecticide groups is probable when trying to manage these 3 major pests in this crop.

Management strategies aimed at reducing or preventing resistance will help prevent resistance from developing and conserve existing products for ongoing use.

Background

Since its 2006 detection in New Zealand, TPP has been responsible for yield and quality-reducing damage to potatoes as well as to other solanaceous crops such as capsicums, tomato and tamarillo. TPP is best known as the insect vector for the zebra chip disease-associated bacterium Candidatus Liberibacter solanacearum but feeding by TPP on potatoes is also linked to damaging effects.

The general strategy is to reduce selection pressure for resistance by minimising insecticide applications, optimising spray timing, delivering insecticides accurately, rotating between insecticides from different chemical groups and using a pre-planned programme. This is combined with management practices for the crop and surrounding host plants that aim to reduce psyllid numbers (Page-Weir et al 2011, MacDonald et al 2015, Walker et al 2015, Wright 2017).

Note: Control failure does not always imply resistance.

Current Status of insecticide resistance

A study by Plant and Food Research (Watkins et al 2021, sponsored by Potatoes NZ) demonstrated that current contact insecticides commonly used showed no material difference in mortality of adults and nymphs between the ‘wild’ field-collected colony and the susceptible PFR TPP colony for all products tested.

A further study in 2022 (Watkins et al 2022, sponsored by Potatoes NZ) evaluated systemic and translaminar insecticides currently used for control of TPP. Again, no material difference was found in the performance of the insecticides tested.

While both trials were only applied to TPP populations collected around Canterbury, they indicate that there is currently no shift in sensitivity to the insecticides tested.

Insecticides for use in potatoes

The following active ingredients are registered for use in potato crops (Table 1). The key target pests and pest types are also identified (Aphids, Tomato Potato Psyllid (TPP), Potato Tuber Moth (PTM)). It is important to understand all products used for pest insect management in potato crops, as the use of one insecticide mode of action (MoA) group for the control of one pest may limit the opportunity to use the same MoA insecticide group at a later stage in the crop cycle for the control of a different pest.

Do not return to using a product from the same MoA group for at least one insect generation (4 weeks or more).

This strategy has been written especially for TPP.

Crop management

• Psyllid monitoring: To help identify the first influx of adult TPP, or peaks
  in adult numbers. Yellow sticky traps should be placed slightly in from the edges
  of potato fields, just above crop height, and changed every 7 days.  Identify, count and record adult TPP.
• Crop scouting provides valuable information on whether TPP has established, the life stages present, and their numbers.
• Knowing the life stages present in the crop means you can target insecticide applications (especially early season when there is less overlap between generations).
• Recommended method: count 2 middle leaves (of different stems) from 50 plants (i.e. 100 leaves from 50 different plants). This gives a reliable estimate of TPP infestations.
• It is also important to have a look well into the crop for eggs and nymphs each week.

Insecticide use

• Always read the label and use as directed.
• Rotate between different insecticide MoA groups. Even if an insecticide is very effective at controlling TPP it must not be used repeatedly. Note maximum number of applications per crop or season in Table 1 and on the product label.
• Do not spray a product from the same MoA group for more than 4 weeks (or as per label directions). Unless the label states to do so - do not return to using a product from the same MoA for at least one insect generation (more than 4 weeks).
• Broad spectrum insecticides such those from MoA groups 1 and 3 should be used sparingly and best reserved for end of cropping cycle to minimize disruption of beneficial insect populations. (Refer to product labels for specific information).
• One of the most important factors in TPP control is ensuring thorough coverage of plants.
• TPP are usually found well within the canopy of the plant, and often on the underside of leaves. This means it can be difficult for agrichemicals to reach TPP on mature crops. To ensure thorough spray coverage growers should use adequate water rates and spray technologies such as angled nozzles and air assist boom.
• The addition of appropriate adjuvants and the use of products with trans-laminar or systemic properties (products which spread through the leaf and/or plant) should help improve control.
• It is also important to check the pH of tank water to ensure agrichemicals do not lose activity due to hydrolysis.

IPM in potato crops

The use of IPM principles is critical in ensuring insecticide resistance within TPP populations is minimised. IPM relies on the use key predator and parasitoid populations building up within potato crops to control TPP life stages. The use of selective insecticide products during the early to mid-stages of a crop will conserve resident natural enemies and enable these populations to build.

IPM research at Pukekohe and in Waikato commercial crops has validated reduced spray programs that are important additions for IRM for TPP (MacDonald et al 2015; Walker et al 2015). This is due to major reductions in number of insecticide applications required, being 10 less applications in early crop ‘fresh’ potatoes using validated action thresholds, and halving applications in summer main crops from about 10 to 5 sprays by applying a mineral oil alone every second week, rotated with selective insecticides plus oils (MacDonald et al 2015).

As part of the IPM program, and a sound resistance management strategy, regular surveys (every 5 years) of susceptibility of TPP, and other key pests, to commonly applied insecticide products should be undertaken in the major potato growing regions.

References

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