Threat of rose thrips voiced at soft-fruit day

The annual East Malling Research Association/AHDB Horticulture Soft-Fruit Day at the renamed NIAB EMR in Kent on 23 November updated growers on progress made by levy-funded research on pest and disease control.

ADAS senior research entomologist Jude Bennison said rose thrips (Thrips fuscipennis) "is native and has never been a problem but now poses a threat to the strawberry industry. We have been seeing bronzing almost identical to that caused by western flower thrips (WFT, Frankliniella occidentalis) even where that was controlled by IPM. The lighter-coloured WFT is already resistant to most insecticides. Tracer is effective for spotted-wing drosophila (SWD), so save it for that in the season. We need an effective biological control for rose thrips, perhaps an entomopathogenic fungus."

WFT can already be controlled by the predatory mite Neoseiulus cucumeris, but because both pest and predator are so small it can be difficult for growers to monitor establishment, said Dr Jean Fitzgerald. As part of AHDB project SF 156, "based on sampling we did last year, the best strategy to assess for both is to monitor 'button' fruit", she said. Work is now focused on determining predator/prey ratios in relation to crop damage.

In the same project, Dr Tom Pope of Harper Adams University carried out a polytunnel-based study and leaf bioassays to assess aphid controls in strawberry. The polytunnel experiment showed that Hallmark (lambda-cyhalothrin) provides effective control of potato aphid on overwintered strawberry plants, unlike Calypso (thiacloprid) and Chess (pymetrozine), though Calypso, as well as Hallmark, was effective in the assays.

Fungicidal sprays

Also in SF 156, NIAB EMR researchers have investigated the possible toxic effect on predatory mites of fungicidal sprays, including in combination. Mixes of Nimrod (bupirimate) and Teldor (fenhexamid), and of Signum (boscalid+pyraclostrobin) and Systhane (myclobutanil+ cyclohexanone) "can be harmful to N. cucumeris, particularly if repeated in a spray programme", they found, and urged growers to control thrips and tarsonemid with biological controls early in the season before chemical insecticides are required against SWD.

On fungal control, NIAB EMR research leader Dr Angela Berrie said: "Powdery mildew can get very bad in late-season crops and modern varieties are more susceptible. It can come in on plant material, and fungicides aren't always effective, especially on everbearers. Then we have the loss of actives like Systhane. The current approach isn't sustainable and we need a new one, incorporating biocontrols and biostimulants in programmes."

A trial begun last year, initially stymied by low powdery mildew incidence, tested 10 commercial and trial biocontrols individually and in combination against conventional fungicides. Though all treatments "significantly reduced" mildew, the grower considered the control achieved to be "not commercially acceptable".

A second trial this year at EMR and ADAS showed high mildew incidence and is currently being evaluated. "Hopefully this approach will give better control of mildew, particularly in long-season everbearer production," said Berrie.

On raspberries, NIAB EMR entomologist Dr Chantelle Jay said of attempts to integrate overhead spraying with biocontrol of two-spotted spider mite: "Control of SWD is key to these experiments." After modifying the boom design and nozzle type from last year, this year has shown that "the booms appear to keep down SWD numbers as well as the knapsack sprayer did".

On raspberry root rot control, ADAS pathologist Dr Erika Wedgwood said: "You can spread it by reusing water and it can be in plant material, though you can't see it," adding that soil sterilisation "is now limited". The SF 158 project is looking at "plant strengthening products" as well as biofungicides, "but it is early days on this".

On bush fruit, Michelle Fountain and colleagues are working to develop pheromone traps for gooseberry sawfly (Nematus olfaciens) and blackcurrant sawfly (N. ribesii). "We want to develop something that will last all season but are not near to producing a pheromone at this stage," she said. "Next year we will work to correlate numbers caught in standard red delta traps with crop damage and with numbers of natural enemies."

Her NIAB EMR colleague, research technician Maddie Cannon and her team, have meanwhile been surveying earwig numbers in blackcurrant crops in five widely dispersed areas. "There are big differences, even on the same farm," she said. "That may be down to soil, mowing or herbicides, which we are looking at now. The revocation of the aphid control Aphox on blackcurrants means we will have to rely more on natural predators."

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