Biopesticides – playing a bigger role

They say that the only constant is change – and this is certainly the case when it comes to crop protection. As growers of protected ornamentals and salads were reminded at this year’s AHDB’s biopesticide conference in Kenilworth, Warwickshire, biopesticides – that is, plant protection products based on living microbes and natural products such as plant extracts and insect sex pheromones – are likely to play a bigger role in future. With this in mind, AHDB’s five-year AMBER (Application and Management of Biopesticides for Efficacy and Reliability) project is finding out how best to help growers get the most out of these products, Rachel Anderson reports.

The start of a “green” revolution

Growers of protected crops would certainly agree that integrated pest management is the way forward – not less because it is part of the European Union’s Sustainable Use Directive on pesticides. Warwick Crop Centre’s Dr Dave Chandler, who is leading the AMBER project, predicted that, given the global concern surrounding chemical products, this approach will continue after Brexit. “I think the number of synthetic chemical pesticides available is going to go down quite a lot. There’s real concern about the impact that intensive farming is having on insects, for example, so, I think that the pressure on farming is only going to increase.” He added: “We need a new green revolution in farming and growing – one that will be sustainable and protect the quality of products without affecting the environment.”

Horticultural consultant Chris Need, warned delegates of the increasing public concern surrounding chemical residues. He noted, for instance, that a German research station has been analysing the chemical residues on a range of ornamental crops. “Whilst there are no MRLs [maximum residue limits] for ornamentals, there is a lot of interest in Europe about this. So, if they are looking into it, then our retailers will probably follow at some stage.” He added that, sofar, he hasn’t found any evidence that any British retailers are testing for residues on ornamental crops – “but it’s certainly something that we should all be bearing in mind.”

Whilst we may not quite yet be experiencing a “green” revolution, the crop protection market is undoubtedly changing. As Andy Brown, secretary of the International Biocontrol Manufacturers Association (IBMA), noted: “There are currently more new biological active ingredients being registered than synthetic chemicals.” In fact, the biocontrol market has grown by more than 300% between 2008 and 2018. Andy said: “It’s growing at about 19% a year in the UK, compared to the synthetic chemical industry – [which is growing at] 2% or 3%. Admittedly, its starting at a smaller value but it shows you how much the industry is changing.”

Whilst growers want to use biopesticides, some remain wary of them because of the inconsistent results they can give. More knowledge on how to use them is undoubtedly needed, which is why AMBER – which is due to wrap up at the end of 2020 – is coming in to help. Dave asserted: “AMBER is providing underpinning knowledge so that we can get the best out of these products.”

Lesson one – delivering an effective dose

Having observed how growers have been using biopesticides on both protected ornamental and edible crops, the AMBER project has so far identified two key “lessons” that growers should be aware of. Firstly, they need to ensure that they are delivering an effective dose to the target. This includes, said Dave, optimising water volume and getting the best from their sprayer. The AMBER team observed, for example, that chemical residues in spray tanks have been affecting the performance of biofungicides. “I am going to moan at you. You are not changing your nozzles properly. Are you carrying out proper maintenance on your sprayers? Are you investing in the best technology that you can? You will need to now because, in new crop protection systems, there’s no margin for error.”

Clare Butler Ellis from Silsoe Spray Application Unit, and Ruud Roeven from Syngenta, gave similar advice to delegates. Clare, for example, emphasised that accurate dosing, water volume, distribution of product and the size of the deposit on the plant (including the solution’s initial droplet size) are key factors to consider when applying biopesticides.

Water volume

Guidelines of some biopesticide products instruct growers to apply them as a specific dose, whilst others are a bit vague. As part of the AMBER project, Clare therefore carried out a trial on chrysanthemums (chosen as they are bushy ornamental plants with lots of surface area) that aimed to identify the optimum spray volume. This, explained Clare, is the volume of solution that gives the maximum amount of active substance to the plant with the optimum deposition characteristics. Interestingly, water volumes greater than 100 litres per hectare did not improve the distribution of spray over the plant.

Lower volumes can be achieved, advised Clare, by using a small nozzle. She added that no volume will cover 100% of the leaf surface without something to reduce surface tension. “Biopesticides seem to have very little in the way of spreaders and wetters added,” added Clare.

Ruud from Syngeta noted that, depending on the product, adjuvants can help to optimise the performance of the biopesticides. Trials carried out in the UK on pepper crops showed that XenTari (used to control the twinspot moth caterpillar) performed better when it was mixed with an adjuvant (just over 60% control compared to just over 70% control, for example). Ruud informed The Commercial Greenhouse Growerthat a couple of new biopesticide-related products from Syngenta are expected to be available on the UK market in the near future.

Timing is everything

Knowing the best time to apply a biopesticide is the second key “lesson” so far learned in AMBER, reported Dave. He emphasised that, to apply a biopesticide in its “Goldilocks zone,” growers must understand its mode of action and how it relates to its target pest or disease. Helpfully, the AMBER team is using, and developing, mathematical models to help identify optimum biopesticide application strategies for growers.

Understanding your biopesticide

Jude Bennison, senior research entomologist at ADAS, and ADAS plant pathologist Aoife O’Driscoll, have been investigating what happens to the organisms in biopesticides once they are sprayed onto the crop. Aoife asked: “If you apply the recommended dose, how long do the organisms survive at a level that will control your diseases? If you apply them preventatively, before there are any pathogens present, what are the best conditions to spray them in, and what are the number of organisms you need to get effective control of your disease?”

The experiments have so far found, for example, that a viable population of Prestop (Gliocladium catenulatumstrain J1446) lived on the foliage of tomato plants for up to 14 days after it was applied to the leaves when there was no host present. Aoife said: “In the absence of any food source, when you apply the G. catenulatum, the number of spores increased and did not decrease. It has a really, long persistence with no disease present. That’s a really important message to take from this.” She added that the result fits quite well with Prestop’s mode of action. Its technical notes state that it’s a fast-growing fungus that deprives pathogens of living space and nourishment.

Meanwhile, AQ10 (Ampelomyces quisqualis)–a naturally-occurring parasite of powdery mildew – did not persist for very long in the absence of a powdery mildew host. Aoife said: “By day seven, a viable population was virtually undetectable. But this is not a negative result. It just reinforces the message that you need to understand your biopesticide. You need to think of them as having personalities. Treat each one differently.”


How biopesticides perform alongside other forms of crop protection, such as beneficial insects, is another consideration for the industry. ADAS horticulture consultant David Talbot said: “If you are unsure of compatibility and you can’t get any information from your suppliers, probably the best advice we can give is to try and leave as long an interval as possible between the application of that biopesticide and your next introduction of predators.”

“So, if you are introducing a predator weekly, try to angle your biopesticide between releases or maybe even [try] missing releases if you are on top of your pest control.”

David added that product compatibility lists are available – with one having recently been produced for Prestop.

David also reminded growers that biopesticides can complement biocontrols, as was shown last year when the fungus Beauveria bassianawas used as a supplementary treatment to phytoseiulus persimilison tomato crops. “You can see that the number of adult nymphs and eggs were much lower when Phytoseiuluswas combined with Beauveria. This is a useful knockdown treatment that can be used this summer.”

Gaining new insights

Ant Surrage, from Fargro, informed delegates that biopesticides’ performance can also be optimised by understanding a crop’s microclimate – namely, “the environment the plant is feeling rather than the environment that the sensor is feeling.”

The firm has teamed up with remote sensing specialist 30MHz to enable growers to install “lots of little sensors around the glasshouse” that give feedback in real time to help growers start to build up a picture of their crop. The sensors may, for example, show up hot or cold spots – such as where a door is being left open or where there are air flow issues. “We can then start looking at simple solutions to start managing that environment better,” said Ant – who explained that biopesticides tend to have certain environmental conditions where they have maximum efficacy. This technology, explained Ant, transports data onto a user-friendly dashboard, named Zensie, which alerts growers to when environmental conditions are “Goldilocks.” “On the dashboard for the optimisation of Naturalis L, [for example], we have a temperature and a humidity gauge. When they both go green the spray team gets sent a text message to say that the conditions are correct to go out and spray.”

Plainly, both commercial companies like Fargo and 30MHz – and research projects such as AMBER – are helping growers to gain knowledge, and get the most out of, these increasingly important tools. And, as the AMBER team continues its research and passes on its knowledge, growers of protected crops will continue to gain confidence in using these “living products.”