The changing face of plant protection – The Fruit Grower

In the top-fruit sector, because of the impending loss of insecticides such as Explicit (indoxacarb) and Gazelle (acetamiprid), options are becoming increasingly limited, so growers need to understand how to achieve the best possible efficacy from what is still available.

Jonathan says: “One of the challenges will be how to deal not only with the target pest, but also others that have been incidentally controlled by the same active. For example, indoxacarb controls both caterpillars and apple blossom weevils, while Gazelle principally targets aphids but also gives some weevil control. Once these broader-spectrum insecticides are gone, any new products coming through will be more pest-specific, so incidental control will be lost. Moreover, many growers have avoided pyrethroid insecticides for decades so they can build up beneficials, and this insecticide group is likely to be under significant pressure at re-registration over the next five years.

He adds that for Lepidoptera control after flowering, Coragen (chlorantraniliprolel) is expected to remain available, but as it has an EAMU for codling moth in apples, it is advisable to time its use accordingly.

“This means that new strategies will need to be devised for pre-flowering caterpillar control to ensure the level of control that will be sufficient for growing a commercial crop”.

Assuming that indoxacarb is not available for 2025, growers will be looking at available options for codling moth control and assessing their potential efficacy, continues Jonathan. “Coragen will probably still be around, but we need to move towards a more integrated system of control as few or no new insecticides will be coming through”.

Pheromone mating disruption is a strategy with  good potential, he observes, noting that currently there is only one product licenced for GB, RAK 3+4, which, unfortunately, has been commercially withdrawn by BASF. “If all the growers in an area adopt a mating disruption system, then it can be very effective.

“However, the nature of our farming in the UK is patchwork, which means that there are not many joined-up areas that are growing apples. As a result, there are ‘edge effects’, such as unsprayed orchards next to commercial orchards, and while the mating disruption works where it is applied, it does not stop the moths from breeding next door and the females entering the commercial orchard”.

There are some additional concerns in that the product comes in plastic dispensers which need to be put out and collected manually to be disposed of, he adds. “However, we know that mating disruption can be effective when used collaboratively, and there are some alternative off-the-shelf mating disruption products that could be authorised for use in Britain. However, the cost of registering them may well be prohibitive for the size of the market. It will be interesting to see the proposals CRD make for registering alternative controls like this, as this is an important barrier for the market”.

Nevertheless, other interesting products are in the pipeline, he adds. These include a sterile insect technique for codling moth, successfully used in Canada under regional control, and there are new products being developed which we may see in a few years’ time, including peptide-based insecticides and sprayable pheromones, but these are some way off practical use in the UK. “In the meantime, we are seeing good results in controlling codling moth with Madex Top, a biopesticide containing a granulosis virus specific to the pest,” adds Jonathan.

A better understanding of how to use alternative products in a strategy to fill the gaps between conventional products is crucial as they become scarcer, says Jonathan. “There will be no direct replacement for indoxacarb, so control will entail stacking combinations together to ensure that you do not have to deal with such a big population year-on-year. In a similar way, we have also been looking at elicitor and biostimulant products, and how they can help to improve disease control across a range of crops; for example the addition of the biostimulant ProCrop ISR to apple scab programmes has been seen to help make the crop more robust against the disease and in grapes it has helped improve plant health to better fight off downy mildew”.

These products will not replace conventional plant protection products, but have the potential to make programmes more robust, so Hutchinsons are exploring their value in both replicated and commercial scale trials. “There are a lot of products on the market, and they all make some sort of statement about improving plant health or robustness, but it is crucial to put them to the test to sort out which ones add value for the grower. We need to be open-minded and assess alternatives and get them to work with a few growers, as this builds confidence, not only amongst our own agronomists but also when growers discuss a product between themselves. This will help our industry move away from the ‘pest control in a bottle’ mind­ set, towards ‘systems’ thinking. For example, we need to consider the orchard as a biological system and work out how to manipulate the biology in our favour, such as through encouraging beneficials, or the introduction of nematodes and viruses to reduce the numbers to acceptable levels. Insecticides will still be necessary for just that last correction of pest numbers”.

This is a granulosis virus (a type of baculovirus) that infects the larvae of the codling moth and kills them, explains Jonathan, adding that sub-lethal doses will get passed on 10 subsequent generations, so populations tend to decline.

“Commercial growers signing up to use this biological means of control could use entomopathogenic nematode applications in the autumn to reduce the overwintering populations, and Madex Top in the spring,” he says. “What you are targeting is the trunk of the tree, where the overwintering codling moth is found in the cracks and crevices of the bark. Here, the nematodes can find and attack them. September is a difficult time for growers as they will be harvesting, but as the product is best applied in high water volumes and damp conditions. It can be applied when it is drizzling. So, when picking has halted because of wet conditions, there may be a window of opportunity”. This strategy could also be combined with mating disruption in the future, should a product become available again.

However, biopesticides are not as forgiving as conventionals, warns Jonathan. ”If you do not get the timing quite right, a conventional will still usually work relatively well, but a biopesticide may be less effective”.

Even in a glasshouse there can be times when biopesticides have not worked so well, normally because the grower did not know how to use the product correctly, such as timing or growth stage, or pest lifecycle. Consequently, some growers have returned to using conventionals.

“Biological products need more handholding from agronomists to ensure that they are used correctly, such as timing applications to egg-hatch using pheromone trapping and modelling. This is why we are working to refine understanding of how to get the maximum effect from Madex Top; for example, applications should not be made when it is raining and growers need to be aware that the product breaks down in high UV light but lasts longer in lower UV conditions

Effective control of codling moth and other Lepidoptera species in the absence of indoxacarb is still possible using bioinsecticides such as Madex Top and Delfin, says Iván Velasco, stone- and top-fruit specialist at Hutchinsons. He has been working closely with a grower in Kent who has been trialling Madex Top in a 58ha pear orchard and a 10ha apple orchard for three years.

He is also assessing how well Delfin (Bacillus thuringiensis kurstaki SA-11,SA) works in winter moth and other Lepidoptera in cherry orchards. “One of the challenges in cherry crops going forward will be pre-flowering control once Indoxacarb has gone”, says Iván. “However, Delfin is very safe for pollinators, so it can be applied at flowering”.

While the biological insecticide is aimed at all Lepidoptera species and can be applied to both first and second generations, he observes that it is non-toxic to beneficial insects and predatory mites. In-field trials are underway to determine the efficacy of Delfin on winter moths in pear orchards, reveals Iván, adding that although it looks promising to date, this is the first year large-scale use and more needs to be done to assess efficacy. “Applications are made when the first instar larval stage is reached, and two applications have been made so far this season. Water volume will depend on crop growth stage, and it is crucial to ensure adequate crop coverage. It can also be applied as a tank mix with other products. We’ll continue to trial and evaluate, to further refine our understanding of this new biological treatment”.

A three-year commercial demonstration project to show how effective codling moth control can be achieved in a post-indoxacarb world is planned to start imminently, reveals Jonathan. “Our industry is concerned because the loss of insecticides will make conventional control of hatching eggs and larvae more difficult. Additionally, growers trialling mating disruption have seen mixed results and the only product registered has been commercially withdrawn. With our project partners, Andermatt UK, Koppen UK and Landseer, the project aims to show that growers can achieve commercially realistic levels of codling moth control using currently available products and techniques. but without using indoxacarb. Controls will initially focus on using Madex Top for in-season control, with careful timing of applications driven by automated TrapView pheromone traps. This will be augmented with autumn applications of Capirel (Steinemema feltiae) entomopathogenic nematodes to reduce over-wintering adult codling moth populations. We plan to have at least two commercial orchard sites up and running before the end of May and will be inviting the industry to share in the findings as we go along”.