Article taken from The Fruit Grower magazine
By Rachel Anderson
Tackling tree fruit pests, and boosting orchards' health and biodiversity, are topics that continue to be at the centre of much of the research that is carried out at East Mailing Research (EMR). Entomologist Dr Michelle Fountain discussed some of these themes at the Agrovista Fruit Technical Seminar at Brands Hatch, Kent in January. Dr Louise Robinson-Boyer, of Kent-based firm PlantWorks, also gave a presentation at the event, where she explained to growers that they can boost the wellbeing of their orchards if they pay more attention to the soil.
Rhynchites weevil
Petal fall is the best time of year for growers to tackle the rhynchites weevil - an increasingly common pest in apple crops. This is one of the useful tips to come out of a project researching these insects that is part of a wider AHDB Horticulture project on the integrated pest management (IPM) of tree fruit pests and diseases. Dr Fountain told delegates that data collected by researchers at EMR showed that peak numbers of the pest were found at petal fall. She therefore advised growers to ""Spray as soon as the petals have dropped. Put the spray on post-petal early so you get them before they start to lay eggs."" She added that the discovery of this peak in weevil numbers is encouraging because it means that growers do not need to spray when the trees are in flower. She warned growers against spraying at this time because of the possible risk to bee populations. She said that, given the grave concern about bee health: ""It's quite a good thing for the industry to be careful until there's more evidence.""
Michelle also reminded growers that, due to label changes, they can no longer use chlorpyrifos post-flowering. Other trials, she revealed, have examined whether certain apple cultivars are more attractive to the pest - which can cause losses of 1% to 5% of a crop. The research team's results found that there may well be some differences in weevil populations between varieties. However, she said that a more significant find was the fact that the weevils, which cause corky scars on apples when they feed on the fruitlets, appeared in the trees the moment the trees broke their winter dormancy. She said: ""The first weevils on apples trees appeared when the first bud scales were visible."" She added that weevils are present in fruit trees from when the leaves start to appear and until June drop. But whilst scientists are starting to gain a better understanding of weevils' presence in the crop, Michelle told delegates that it is not yet clear exactly how the pests mate. An earlier investigation at EMR had hoped to identify a pheromone that could be used for monitoring purposes. Part of this project therefore tested the weevils' reaction to various different chemical compounds. The researchers were looking at both aggregate pheromones, which attract both sexes, and sex pheromones produced by the females. But Michelle said that, unfortunately, the results found ""no suggestion of attractive compounds from male or female rhynchites."" However, she did mention that the weevils responded to benzyl alcohol, which is found in plants.
Meanwhile, trials carried out in the orchard observed that the females prefer to be far apart when they are laying their eggs. Michelle said: ""If we put a female in a baited trap in a tree we did not find many other females there when they were laying their eggs. They could be dispersing."" She advised growers to keep on monitoring for the pest by tap sampling apple branches over a white tray. She admitted that this might be a frustrating activity given that the EMR scientist had to tap sample a minimum of 15 trees to find just one weevil.
Earwigs
Growers should be wary of the cumulative effects that their crop protection programmes could be having on earwigs, which are now known to be beneficial creatures in orchards. Dr Fountain told delegates that EMR has carried out, and is continuing to work on, research that is striving to develop an earwig-safe spray programme for apple and pear orchards. This is because earwigs prey on pests such as aphids, pear sucker nymphs and eggs, caterpillars, and codling moth eggs, larvae and pupae. So far the research has measured the short-term toxicity of ten different pesticides that were tested in a laboratory. The research has also included field trials that compared an 'earwig-friendly spray regime with a standard pesticide programme. The laboratory tests found that some of the products were having an effect on the earwigs and so, over time, they could have an effect on orchard populations. Chlorpyrifos, for instance, caused a significantly higher level of mortality than the other products. Spinosad also stood out in the trial as, after chlorpyrifos, it resulted in a lower number of surviving earwigs than the other products. A handful of pesticides were then tested on a plot outside but the results largely showed that the products were causing no significant difference to earwig numbers. Michelle said that the EMR team wondered whether this was because the plots, which had just six trees in each, were too small. A further trial was therefore carried out on two commercial farms in Kent -Broadwater Farm and Rodmersham Court Farm. Each farm had an orchard that received a standard spray programme and one that received an 'earwig-compatible' programme.
Assessments were carried out in spring, summer and late summer. Michelle told delegates that, whilst there were more earwigs found in the trees treated with the 'friendly' programme, the results were not straightforward. Some orchards had barely any earwigs in them, whilst some were full of the creatures. For example, the conventionally-sprayed orchards in Rodmersham had just 15 earwigs by the end-of-summer assessment and the 'earwig-friendly' orchard had 309. Meanwhile, the conventionally-treated orchard at Broadwater had an impressive 5,632 earwigs - which was even more than the 5,165 that were found in the farm's `earwig-compatible' orchard. Dr Fountain therefore told growers that this indicates that they could still apply products to an orchard providing that it has robust earwig populations. Growers just need to avoid using earwig-harming pesticides at key times of the year, such as from May onwards when there are young earwigs present. She said: ""Occasional applications of Gazelle or Calypso for early season pests are unlikely to have long-term effects if earwig populations are high."" She also urged growers to keep monitoring their earwig populations - such as through tap sampling or by going out in the evenings when these nocturnal creatures are about. She asked growers: ""On your farms, do you know which orchards have healthy predator numbers? And if you don't, what can you do to help?""
Boosting farm ecology
Ways in which growers can speed up the ecology of new orchards is the focus of a five-year AHDB Horticulture project that EMR is helping to conduct. Dr Michelle Fountain told delegates that this piece of research is particularly important, given that today's horticultural practices are increasingly intensive. She added that the project has so far put pollinators, which are an essential part of fruit production, in the spotlight as ""currently there is not much concentration on pollinators in our best practice."" Researchers have therefore been analysing which pollinators frequent certain crops with a view to developing ways of better understanding their habitat needs. Michelle revealed that the pollinators in apple and pear orchards were analysed, as were the pollinators in eight blackcurrant plantations. The results showed that many different pollinators forage on these crops - including honeybees, bumblebees, hoverflies, and wasps. Interestingly, solitary bees, which do not live in colonies, were the pollinator that most frequently visited the blackcurrant and apple plots, whilst honeybees were the most frequent visitor to the pear plots. Meanwhile, solitary bees were the second most frequent visitor to the pear orchards.
Michelle said: ""Andrena dorsata and Andrena haemorrhoa are common solitary bees on all three crops."" Dr Fountain also revealed that the researchers looked at what happened when the pollinators were taken away. Arguably, the results spoke for themselves, as when the plants were put inside a pollinator-free `tunnel' only two-thirds of the pear fruit set and a little over 20% of the blackcurrant fruit set. Michelle also told growers that future aspects of this particular project are likely to focus on the habitat needs of `the key players' and which pollinators are the most effective. She also pointed out to growers that another reason this project is being carried is that new orchards are often vulnerable to outbreaks of pests and diseases. ""What often happens in new orchards, because you've not got many of your predators, is that you get sporadic outbursts of pests."" However, she noted that there is a lot that can be done to help the orchard reach its 'ecological climax', to the point where such problems subside. Such helpful practices include having flowering crops in some of the alleyways and incorporating mycorrhizal fungi into the soil. Dr Louise Robinson-Boyer told delegates that PlantWorks manufactures these particular fungi - which, she explained, help plants tolerate stress.
""Microbes are a real possibility for aiding sustainable crop production," she said - adding that land managers are now starting to consider the importance of the area `below ground' by reducing their tillage and introducing crop rotations, worms, organic matter and beneficial insects. She also explained that the use of excessive amounts of pesticides and fertilisers is damaging the mycorrhizal population in the soil. But this mycorrhizal fungal network, she said, increases the active uptake surface of roots by up to 700 times, so it's a site of transfer for nutrients. Dr Robinson-Boyer told delegates that, until very recently, PlantWorks had mainly supplied the gardening market. However, as commercial growers have started to cotton on to the benefits of these fungi, industry trials have started to take place. She said: ""Collaborations with research and industry are increasing our understanding of efficacy."" So far work has included trials with the seed houses Cotswold Seeds and Limagrain, who are examining its value in animal feed crops. Meanwhile, agronomy firm ProCam is trialling the product on potato and wheat crops and trials at EMR have already shown positive results on strawberries. Dr Robinson-Boyer explained that arbuscular mycorrhizal fungi (AMF) -which are found in most plant species - were added to the coir substrate and the result was an increase in Class 1 fruit, improved plant growth and a better tolerance to drought. She said: "[There was] an average 10%-20% increase in Class 1 fruit in coir substrate, using commercial fertigation."" The strawberry plants also required less water, she said, ""with 40% less irrigation."" Dr Robinson-Boyer added that the product has also been trialled on trees - although not in a commercial orchard. Rather, it was tested on woodland trees such as oak, beech, birch and ash. Those trees that were growing on the treated soil established, and grew more robustly, than the untreated trees, she said. Dr Robinson-Boyer therefore pointed out to growers that having such microbes in the soil is commercially beneficial. ""You may not need the same amount of crop protection. I'm not saying completely take it away - maybe just a reduced requirement.""
Spotted Wing Drosophila
Fruit growers should start deploying their spotted wing drosophila (SWD) monitoring traps in the hedgerows and woodlands of their farms from the end of February. This was the advice given to growers by Alex therefore emphasised that, as growers need to ensure that control measures are put in place as soon as adult pests are found, ""monitoring is a very important starting point"". He also pointed out that, as the season progresses, growers must alternate the products they use because the risk of the pests becoming resistant to plant protection products is very high. But before they start applying any chemicals, Alex advised growers that, after deploying their initial traps in woodlands in February, they should start putting traps amongst their crops from March. They could, he added, even consider precision Agrovista's fruit agronomist Alex Radu, who reminded delegates that SWD is monitoring, when now an established pest in stone and traps are placed soft fruit crops. around the outside perimeter of the crop before it ripens, because this practice has ""some success in delaying SWD entering the crops," he said. Alex advised growers to use the modified Biobest Droso traps with additional holes - the same trap that was recommended to growers in 2015.
However, he also reminded them that as the season progresses ""The fruit becomes more attractive than the traps themselves."" Focusing this year's talk on cherry and plum crops in particular, Alex noted that fine nets can also help to delay the time it takes for SWD to enter the crops. However, he pointed out that all covers and nets should be removed as soon as harvesting is finished. ""It's important to remove the cover just as soon as you finish harvesting as birds will start to eat the remaining crop and that will reduce the buildup of the SWD, population."" Alex explained that the likelihood of the pest building up resistance to pesticides is high because its Recycle can be quite rapid - as little as 12 days. He said: ""Relying on the same plant protection products is a big mistake - if you keep relying on a couple of products you will select resistant pests."" Alex told growers that there is a relatively limited number of products available to them for treating this pest and that some of the available products can have a detrimental effect on beneficial insects. However, ""it's not at doom and gloom," he said. Products that were approved for controlling SWD on cherries in 2015 included Tracer and Exirel. Other products that can be used on cherries include Hallmark with Zeon technology, Reggae, Calypso, Gazelle, Pyrethrum 5EC, and Spruzit. The products that can be used on plums include Tracer, Hallmark with Zeon technology, Pyrethrum 5EC, Spruzit and Gazelle. Delegates were also reminded to follow AHDB Horticulture's recommended ways of treating SWD-affected waste fruit, which includes enclosed composting.
Growers Choice Interactive
A new apple sawfly (Hoplocampa testudinea) model is due to be added to Agrovista's online pest and disease forecasting service, Growers Choice Interactive (GCI), this spring. Alex Radu informed growers that the new model will show growers the egg-laying females' activity, the development of these eggs and therefore ""the best time for insecticide application."" This imminent addition to GCI will see apply sawfly join a list of several other pests and diseases that can now be managed through the system, including a fireblight (Erwinia) model that was added to GCI last year, and a new canker (Neonectria) model. Alex reminded growers that the system also monitors codling moth and scab activity and is able to calculate the level of risk of infection using the data it collects from its many weather stations. He said: ""Depending on the farm, on the weather station, the situation can vary significantly."" He therefore stressed that it's important for growers to time their insecticide applications according to information given by the GCI model.
Apple scab
Top fruit growers now have another way of controlling apple scab (Venturia inaequalis) and pear scab (Venturia pyrina) as BASF's new fungicidal product Delan Pro has just been given the official stamp of approval by Government. Simon Townsend, agronomy manager for BASF, told delegates that Delan Pro is a combination of a new formulation of dithianon (125g/1) and potassium phosphonates (561g/1). Describing the new product, Simon explained that KHP, the potassium phosphonate part of the product, marks ""the first registration of KHP as a fungicide for top fruit."" The product's release is timely because its follows changes that have been made to the label of another scab treatment, Dithianon WG. These changes have made Dithianon WG ""less robust than the old label."" Differences between the old label and the new include the description of the product's effect — which has gone from being ""for the control of"" to ""for the reduction of"" apple and pear scab."" Additionally, the number of applications of Dithianon WG that growers can use has been reduced from 12 to six times a year and the dose rate has been reduced from 0.75kg/ha to 0.5kg/ha. Simon added: ""Our approval has been granted on the assumption that growers' use of dithianon-containing products is restricted to 2.1 kg/ha/year."" Simon also reminded growers that another BASF product, Dithianon Flowable, has now been withdrawn. He explained that the final sales of this product took place in November 2015 and added that stocks of Dithianon Flowable must be used up by November 2016. However, he noted that the arrival of Delan Pro onto the market would ensure the continued use of dithianon as a ""robust 'stand-alone' spray."" He pointed out that the product may even have the ""potential benefit for activity on powdery mildew and moderate Nectria control"", although he informed growers that Delan Pro should not be used on crops destined for cider or perry production. He also advised growers to keep a close eye on the product's maximum residue level (MRL), which is currently 75mg/kg for pome fruits. He said: ""Producers should carefully manage the risk of phosphonate residue accumulation and possible MRL excesses caused by the additional use of other phosphonate-generating products, including unregulated foliar fertilisers."" Simon added that, as well as the new Delan Pro, BASF has also brought onto the market a new formulation of the growth regulator Regalis Plus that includes a built-in water conditioner.
Tackling codling moth
Trials on a promising new IPM programme that is tackling codling moth have had promising results for a second year running. Simon Townsend reminded growers that codling moth is a particularly challenging pest as its hatching larvae quickly bore into fruit, making it difficult to control with insecticides. He also noted that it has been reported that the pests has developed resistance to pesticides. In 2015 BASF therefore ran a second trial to test the combined effects of the insect mating disruptor pheromone product RAK 3+4 and BASF's biopesticide Nemasys C (a nematode solution containing Steinernema carpocapsae). Simon said: ""The objective is to fill the orchard with pheromones and confuse the poor old males so they cannot find the females."" The trial took place in an old Gala orchard near Wisbech, Cambridgeshire and had similar results to the previous trial in 2014. Simon explained that the reference orchard had 60 or 70 codling-infected fruits per 1,000 whilst the orchard that received the IPM treatment, which sees Nemasys C applied later in the season, had just one or two per 1,000 fruits. ""We are very pleased as it was a high pressure orchard," said Simon. The RAK 3+4 product has yet to be approved in the UK but is currently approved for use in Belgium. •