Article taken from The Fruit Grower, March 2018, written by Rachel Anderson.
Tackling woolly apple aphid
Top fruit growers looking to control the problematic woolly apple aphid (Eriosoma Lanigerum) are likely to gain access to Bayer's spirotetramat SC100 this year.
Tim Lacey, Bayer's campaign manager for horticulture, informed delegates that this insecticide, that last year received an EAMU (Extension of Authorisation for Minor Use) under the name Movento Top, is expected to acquire either another EAMU or full approval this spring. He noted that, if it receives an EAMU, it will be for treating woolly apple aphid infestations only, but if it receives full authorisation it will be for use against other sap-sucking insects, including mussel scale, leaf curling midges and pear sucker. Tim said: ""Its main targets are any kind of pests that are sucking the sap out of the phloem."" A full authorisation would also see the product gain approval for use on other fruit crops, including outdoorgrown cherries and plums (for the treatment of aphids), outdoor-grown currants (for aphids, leaf midge and gall mite) and outdoor and protected strawberries (for aphids and tarsonemid mite).
Tim informed growers that spirotetramat disrupts the insect's lifecycle by inhibiting its ability to biosynthesise lipids. ""Insects are very dependent on lipids for their metabolic needs - energy, reproduction and metamorphosis."" Examples of the pesticide's effects on sucking pests include eggs that fail to hatch, poor larval development and the deposition of non-viable nymphs. ""It's not a knock-down product," asserted Tim, who stressed that getting the timing right is key with this product. ""Activity is mainly through ingestion of the active substance, so pests must be actively feeding. Get the timings right - don't leave it too late! Apply early in the pest's lifecycle for best effect. The young are more susceptible than adults."" He recommended that the product be applied from the middle to end of May, when the woolly apple aphids are just starting to move from the new colonies towards new growth. He also claimed that the product, which should not be applied before the end of flowering, is unique because of its two-way systemicity, which means that, from where it's been sprayed, the pesticide moves up and down the plant to new tissue.
The quest for canker-free trees
As the top-fruit industry continues to endure canker (neonectria ditissima) infections, there is now a renewed international focus on examining how this fungal disease develops during the nursery phase of production.
NIAB EMR's plant pathology research leader Dr Robert Saville explained that this renewed focus is helping researchers to understand the biology of the disease so that they can design practical management strategies as part of their quest to find 'the holy grail' of developing canker-free trees. He highlighted that there is a risk of canker infection at each of the key nursery stages, from producing the source material to storing and dispatching the young trees.
Fortunately, researchers in the UK and across the globe are examining some of these periods of risk.
UK-based canker research
Robert noted that one of the aims of an AHDB PhD studentship is to develop an easy-to-use canker detection tool so that asymptomatic infection can quickly be localised. So far, research carried out by PhD student Leone Olivieri has seen an apple branch artificially inoculated with the plant tissue. Robert said that, so far, preliminary data shows that asymptomatic tissue is present in the sapwood, but not the bark.
Meanwhile, a strand of the AH DB-funded project TF223 has the potential to lead to the eradication of asymptomatic infection in mother trees, revealed Robert. It is seeing a Fertinyect tree injection device used to treat canker-infected trees by injecting them, through the trunk, with various products, including fungicides, biologicals, defence elicitors and plant health promoters.
Robert reminded delegates that the 2016 trials looked at how the treatments can be used to prevent the expansion of existing canker infections. ""We measured the area of the existing canker, applied the treatments and assessed the change in lesion area over time."" Perhaps disappointingly, the results of these trials were highly variable, and so the idea for the 2017 trials was, said Robert, ""to reduce that variability to test more combinations of the treatments."" The trees were inoculated and the treatments applied when the canker sizes were the same. The lesion growth rates were measured, but the results were once again disappointing.
""Although we did manage to reduce the variability with our new methodology, we did not see much reduction in the size or growth rates of cankers with our different products."" He added: ""Going forward with this, we need to look at different products. We've got the right system, we are getting the products in, they're circulating around the tree, but we haven't yet got the right treatments [with which] to go forward.""
Another element of TF223 is the testing of various soil amendments, such as biochar, to see if they reduce transplant stress and the expression of latent canker ""in those crucial first three years of orchard establishment."" This new research includes a trial on a stool-bed that has been inoculated with canker, said Robert.
Furthermore, a new, four-year, BBSRC-funded project is looking into exactly what triggers canker expression, the switch from latent to pathogenic form. Robert explained that when all the interactions between the pathogen, the host plant, endophytes (micro-organisms that live inside the plant tissues) and the environment are right, ""you get the disease.""
""We know any latent canker in the tree is coming out in the early establishment phase, and we want to look at the biology behind this a bit more.""
International research
Robert revealed that New Zealand's Plant and Food Research has been working on developing propagation methods that are less favourable for canker development. Researchers have been evaluating budding techniques, commercially-available tapes and post-budding treatments. They've so far found, said Robert, that certain techniques and ways of grafting are more susceptible to canker than others. ""T-budding is the least favoured method of propagation," he said.
Robert also said that researchers at the Netherlands' Wageningen University are starting a new project this year that aims to develop a new Dutch quality label for trees.
""They are getting empirical data on the different risk periods of infection through the nursery stages."" He added that, based on their analyses, researchers are developing different control measures for the propagation phase of top-fruit trees, items such as rain covers to protect nursery stock at the growing-on phase. Robert said: ""The idea would be to bring all of this together and generate a protocol for nursery production. The companies that follow this would get a Dutch quality label on their trees. So, this is one to look out for.""
Getting the correct leaf-to-fruit ratio
Fruit grower John Portass of Wisbech Contract Farming became the first grower to address the Agrovista Fruit Technical Seminar when he spoke on the important subject of thinning. As Paul Bennett, Agrovista's technical head of fruit, explained: ""We thought it would be a good idea to have a grower address the subject of thinning, because the pressure is always on how to produce the best quality fruit in the right size-bands without spending too much money.""
John shared his thinning techniques as well as some of his costings and results, all of which no doubt gave some of the growers in the audience some ideas and inspiration. ""An effective thinning programme will be key to our future success," he asserted, revealing that his business supplies fruit to M&S, Waitrose, Tesco, Co-op, Aldi, and Delmonte. Driven by these brands, the farm now aims to grow 65 tonnes/ha of Gala, a level much greater than the 40-50 tonnes/ha that he grew a few years ago. John said: ""We probably felt we were growing our best quality fruit at that stage, and as we've increased our volumes over the years with new systems, there have been times when that eating quality has deteriorated."" He added that, as the farm does not want to compromise the quality of the fruit, ""what we work on is to get the correct leaf/fruit ratio. We want to produce consistently good crops year-on-year and not be biennial.""
John noted that, in the past, he has spent as much as £2,000/ha on thinning which, given the industry's rising inputs and diminishing returns, ""today we can't justify."" With these concerns in mind, John shared the approaches to thinning that his business has developed over the past few years.
Tree shape
""Tree shape is important," asserted John, who revealed that his farm, which features post-and-wire systems on ""good, moisture-retentive"" soils, has changed the shape of its trees and its canopy over the past few years. ""Modern orchard design allows for the effective use of fruitlet thinners, allowing for a reduction in labour inputs," he added. John revealed, for example, that one of his Gala orchards features a tall, slender tree with a maximum width at the base of 60cm and 30cm at the top. The trees have ""very good light distribution"" with few shady areas. ""We like it to be an open tree with good spray penetration. If I'm walking through the orchard in the mid-summer I want to be able to walk through the trees and see three or four rows into the orchard. It's not a fruit wall, it's a very slender spindle cropping on one to four-year-old lateral branches."" He noted that these tree shapes are maintained by mechanically pruning them and hand-pruning when necessary.
Darwin blossom thinner
Whilst some growers swear by this machine, John told growers that he doesn't like the negative effect of the Darwin blossom thinner. ""It definitely works, and it's fairly cheap, but we feel that we get more elongated fruit with the Darwin, maybe due to the hormones produced?"" He said that other effects of the Darwin include poor fruit shape, inconsistent fruit counts, a risk of russeting, and canker infections.
Spray regime
John said that the farm uses a mixture of thinning regimes, depending on what best suits that season. Typically, he starts with the foliar nutrient ammonium thiosulphate (ATS) after the orchards' pollination and fertilisation conditions have been assessed. ""We just want to get rid of the fruit on the one-year wood," he said. This process is carried out two or three times, with each spray covering a different part of the tree. ""For example, we would target just the bottom of the tree if the one-year wood was coming out of there first.
Then we would spray the whole tree or maybe just the tops of the trees."" He then uses fruit thinners including Brevis and MaxCel, noting that Brevis is particularly effective. He revealed, for example, that a trial he ran two years ago comparing Brevis with MaxCel saw Brevis thin 35% of fruitlets and MaxCel thin 20% of fruitlets. He also noted that MaxCel is much more temperature-dependant than Brevis. ""You need to have three to five days of quite warm days in June.""
Hand thinning - ""the final operation""
John said that he hand-thins when necessary and that this typically starts in mid-June. The farm thins down to singles and doubles and removes any poor-quality fruits. ""We aim to achieve that by mid-July," he says.
A worthwhile investment
The average cost of John's thinning regime is, he revealed, around £685/ha or £10.54/tonne. Arguably, this is a worthwhile investment, given the difference in returns it brings. He showed a slide, for example, that compared the difference in returns between a non-thinned orchard with a 70% grade-out and a thinned orchard with a 90% gradeout. The non-thinned orchard returned £0.37 /kg, whilst the thinned orchard returned £0.4 7 /kg. The income/ha (after thinning costs had been deducted) on the non-thinned orchard was £24,050 whilst the thinned orchard was £29,580. John said: ""For us, effective thinning has increased our profitability.""
If you can measure it, you can manage it
Whilst the UK's top fruit sector has not yet fully embraced precision farming techniques, factors such as rising labour costs and the uncertainty surrounding Brexit mean that ""it's not something that growers should be shying away from.""
This was the point made by Agrovista's precision system service representative Jack Harris, who added, ""The UK industry is going to have to innovate more to help it move along."" He added: ""It's not going to be the 'be all and end all'. When I talk about precision I want you to think about it as the 1 % or 2% extra that you can add to the other things you are doing, like using the correct chemicals, adjuvants, cultivations or cultural controls, all of that in the toolbox will hopefully help drive yields up.""
He revealed that precision farming techniques that are being used in other crops could benefit the top fruit sector. These include 'above ground' techniques such as flying drones over the farm to map good and poor areas, and 'below ground' techniques such as measuring soil-health using soil-mapping technology. Jack revealed that in December 2017 Agrovista used the Veris U3 in the 4ha Mill Lane orchard near Wisbech. ""It was the first time the machine had been used in an orchard, probably in the world."" Jack explained that these machines take several readings, measuring, for example, the soil's organic matter and pH. Maps, such as an EC (electrical conductivity) map have been created from the readings and will be used alongside tissue samples and fruit counts during the growing season. All this data will help to highlight any subtle variations in the orchard - areas where it might need more care. As Jack said: ""If we can measure it, we can manage it.""
Protecting the integrity of plant protection products (PPPs)
The need to protect the integrity of PPPs by using them sensibly was the topic of several presentations at this year's seminar. Agrovista's David Taylor reminded growers that adjuvants can play a vital role in helping to improve the efficacy of PPPs. David asserted that spending slightly more money on using adjuvants, such as the Discovery range, in a tank-mix will result in cost savings. ""By using these products, we are just trying to improve the products that you've still got left in your armoury, by ensuring that they hit the target, stick on the target, cover the target and break into that target's surface.""
He noted that Agrovista sells the Discovery range of adjuvants for top fruit products, including: Companion Gold - for contact herbicides, Remix (Grounded) - for residual herbicides, Velocity (Transcend) - for fungicides, Roller - for insecticides, and pHruit - a water conditioner.
In a similar vein, Paul Bennett advised growers that, as spring approaches, they should start a well-timed programme for scab and mildew for apples, by using as many different active ingredients as possible. He added that they should follow FRAC (Fungicide Resistance Action Committee) guidelines because ""the challenge is to manage potential resistance issues while ensuring good control of scab and mildew."" He added: ""The really important message is that we are not going to get many more actives, so we really have to look after the products that we've got."" He noted, for example, that products with a single site mode of action, such as Stroby, are more prone to developing resistance, whilst PPPs with a multi-site mode of action, such as Captan, are less likely to do so.
Moreover, Agrovista agronomist Simon Warren helpfully reminded growers that there are plenty of active ingredients that they can use to manage spotted wing drosophila (SWD), populations of which are rising in the UK year-onyear. But he stressed the need to alternate chemicals, to reduce the chances of the pest, that affects stone and soft fruit crops, particularly cherries, building resistance to any of the products. He listed the many actives that are available for use as part of an integrated approach to managing this pest, with the most effective products being: Spinosad (Tracer), Cyantraniliprole (Exirel), Lambda-Cyhalothrin (Hallmark with Zeon technology), Thiacloprid (Calypso), Acetamiprid (GazelleNulcan), and Pyrethrum (Pyrethrum 5EC).
Simon suggested that growers could start with Exirel, that gives crops 14 days protection, and follow up seven days later with Vulcan, Hallmark or Calypso. This could then be followed seven days later with Tracer.""If we were seeing a large amount of activity in your traps or in the field, it might be worth going back to Tracer rather than going back to Exirel and then starting again. You have plenty of applications that you can use.""
Simon also noted that the pest is more active in the morning and in the late afternoon, when humidity is at its highest, so the timing of the sprays will help. He added that using a water conditioner will improve the efficacy of the product. This is due to most chemical actives working best at pH4-6, but most of us living in a hard water area of pH7 -7.5.
Pollen and nectar mixes for orchards
Spring is one of the best times to establish a pollinator mix in an orchard, Agrovista agronomist Tom Johnson pointed out. ""Spring or autumn are the best times; but any time that you can create a very good seedbed is the most important factor when sowing."" He stated that crops need pollen transfer, through wind, self-pollination and insects, to set fruit. But he also warned that planting a pollinator mix to help with fruit-setting is perhaps a little bit more technical than some growers might realise. ""You can't expect to stick your hand in a bag of seed, chuck it out and it will grow - it just won't work like that.""
Tom explained, for example, that growers must first prepare the ground, killing off weeds and cultivating the land to 10cm deep, and then creating a fine tilth at the surface. Moreover, the location of the pollinator mix, and the type of soil, will determine which type of mix growers should use.
""You have to make sure that you choose the right one," asserted Tom, who pointed out that there are lots of different mixes, such as field-corner mixes and alleyway mixes. ""We can advise and manage the correct mixture for your situation.""
Tom also stressed the importance of managing the pollinator mixes after they have been planted. In fact, trials using pollinator mixes in a commercial Hereford cider orchard in 2012-13 showed that management of the mixture is important, to ensure that the beneficial insects return year after year.