Spotted-wind drosophila (Drosophila suzukii) "is a difficult and complicated pest to control" but thanks to a three-year industry and Government-funded research programme "we are learning so much so quickly and need to get that out to growers", AHDB Horticulture knowledge exchange manager for fruit Scott Raffle told this year's British Independent Fruit Growers' Association technical day (25 January).
He explained: "There has to be an integrated approach. Crop hygiene is essential but growers don't like it because it's costly and time-consuming - you have to pick every last fruit including those on the ground, then keep them in anaerobic conditions, then incorporate them into the soil surface."
He said the pest of softand stone-fruit "has now spread to all parts of the UK, with year-on-year population increases since 2012", adding: "We are short of protection products at the moment, though Spinosad appears to give the best control."
The SF 145 project comes to an end this month. "We still need to improve our understanding, including of the use of repellents to make trees less attractive, and attract-and-kill approaches, where commercial development is ongoing, bait-and-spray, and so-called dead-end hosts as well as more work on chemical controls," he said. "We hope a new project will start in April."
Fruit tree canker
On another headache for fruit growers, NIAB EMR plant pathologist Dr Robert Saville, who leads a five-year project to improve integrated pest and disease management in tree fruit, now entering its third year, said of canker in apple trees: "There is resistance in apples but also a lot of susceptibility, especially in newer varieties. There are always wounds in an orchard and always spores. Nursery infection can be a route. The tree loses vigour because of girdling."
Among a range of control strategies currently being tested at the Kent research station are injections of various fungicides, said Saville. "We have tested nine products, including some not approved, but none had a statistically significant effect, either curatively or protectively, while some even showed a phytotoxic effect."
Over the next four years the effect of supplements on tree health is being studied using hyperspectral imaging to detect the disease, while NIAB EMR will also be documenting genomes of variants of the Neoectria pathogen. "All the isolates are very similar, making the problem more tractable in terms of disease resistance," said Saville. Work is also ongoing with the University of Reading on bacterial canker control in stone fruits through "bacteriophages", of which he said: "These have potential to be biological control agents, but that's still a long way off."
Drone-mounted sensors "could be used to detect all sorts of problems including early onset of canker", Yara UK agronomist Mike Stoker told growers. "Danish growers are already using aerial thermal imaging on their Christmas trees. Aphids cause the trees to generate more heat and that can guide your spraying. The technology is growing exponentially, though it takes a while to be approved as a user."
This contrasts with the situation in chemical pest and disease control, according to BASF agronomy manager for fruit and vegetables Simon Townsend. "Due to the introduction of the hazard-base system of EU approvals, new fungicidal actives are few and far between - only two new products have been through the system in the last five years and the next one won't be along until at least 2020," he pointed out. "So we need to look after what we have and companies like ourselves have focused on defending existing products." Speaking about Sercadis, a scab and mildew fungicide now available to apple and pear growers, he said: "It's very mixable so the best strategy is to use it preventively in a tank mix with partner products that are as good." Trials last year at NIAB EMR "showed it also increased leaf size by up to 50%", he added.
On machinery, NP Seymour director Nick Seymour said the German-manufactured Darwin blossom thinner "is now used by over 30 growers, and now by two growers of stone fruit", and "appears to give the tree a wake-up call, leading to greater fruit size and uniformity". Featuring an adjustable spindle speed that can be tailored to blossom density, the new Darwin S model "is on trial this year and will be available next", he added.
Driverless tractors, meanwhile, can already "play back" a recorded route through an orchard, and so can be used to mow alleys automatically, he explained. But using satellite-based GPS systems gives insufficient accuracy in the field, so a real-time kinematic station is required locally to get accuracy down to 20mm. "The full package including tractor will cost around £115,000 plus VAT," he said. "Machines will increasingly carry out routine and repetitive tasks while you get on with something else."
The loss of chemicals is making mechanical orchard weeding more appealing, said Seymour. The Ladurner features automatic tree sensing, while the Braun Rollhacke is adjustable for depth and angle, and can be combined with other orchard operations.
EMR NIAB farm manager Graham Caspell admitted that 2016 was "a complete disaster" for the Kent research station's concept pear orchard, due to a combination of weather factors. Yet the previous year the orchard, where innovative pear-growing formats are being trialled and compared, gave a net return of £24,000, just six years after planting, with the V-format giving more than 70 tonnes of fruit per hectare. "I think double-head will be the way to go, however, as it's more conducive to mechanical pruning, but we have a long way to go on this," he added.
Meanwhile, climate change may mean a longer growing season, but also premature bud break and fruit blossom out of sync with pollinating insects as well as fewer frost days, said Professor Christopher J Atkinson of the University of Greenwich, explaining that under climate change models up to the year 2080: "Blackcurrant yields will increase in Scotland but decrease elsewhere in the UK."
He added: "Climate change isn't consistent or linear and I would put money on variability getting larger. Growers will have to understand and deal with vulnerability. But it is also an opportunity in terms of the crops we can grow."