HDC research yields results for soft fruits

The EMRA/HDC Soft Fruit Day gave growers a vital update on new predator controls, finds Brian Lovelidge.

The value placed by growers and advisers on Horticultural Development Company (HDC)-funded research and development work was clearly demonstrated by the number of visitors to the East Malling Research Association (EMRA)/HDC Soft Fruit Day at East Malling Research (EMR) on 24 November. With more than 110 in attendance, the audience was the biggest at any comparable event held at the centre.

Since the HDC was established in 1986, it has commissioned an impressive number of projects that have solved many problems that growers face, saving them money and enabling them to produce higher yields of better-quality fruit with less labour and other inputs.

Decisions about what lines of research work to prioritise are made by the company's soft fruit panel, comprising 10 growers and eight scientific and advisory members under the chairmanship of the Cambridgeshire grower Harriet Duncalfe.

The HDC is now funding 35 soft fruit projects being carried out by EMR, ADAS and the Farm Advisory Services Team. Thirteen of these were described by researchers at the soft fruit day. Most aim to solve problems of immediate concern, such as western flower thrips (WFT) infestation of strawberries.

HDC communications manager Scott Raffle said that although the pest is a big problem in many other crops it has only recently become troublesome in soft fruit, particularly everbearer strawberries. As a result of the damage the pest causes to the fruit, much of it has been written off.

One reason for this, asserted EMR researcher Jean Fitzgerald, is that the pest has become resistant to all of the insecticides approved for its control, including the newest one, Tracer. Furthermore, the predatory mite used for its control, Amblyseius cucumeris, has proved unreliable in everbearers.

"If you get a lot of (WFT) the predator cannot catch up and quite often growers release it at too low a rate, too late," she said. "So we're looking at different ways of controlling the pest. We've found that it overwinters in the crop and is active as early as March."

She has investigated ways of improving WFT control through better use of A. cucumeris. Treatments involved were the introduction into the crop (Jubilee) of slow-release Amblyseius breeder system sachets or the loose mite at various intervals starting before flowering.

Fitzgerald said that the release before flowering reduced early season WFT numbers and early fruit damage. Although the multiple release of the predator did not significantly affect pest numbers in the flowers, which WFT also damages, it did increase the amount of saleable fruit from the early picks.

"None of the treatments prevented fruit damage (right) through the season," she added. "So on farms with high WFT populations other strategies are needed to integrate with the release of A. cucumeris."

Another cause of significantly reduced income, red berry disease of blackberries, is being investigated by EMR's Jerry Cross and Adrian Harris. Cross explained that although the blackberry mite is thought to be the culprit, it now appears that "there is something else going on that we don't know about" because it has been very difficult to identify blackberry mite as the main cause.

"Red berry disease has become quite serious in the past few years, especially in protected blackberries, with some growers losing up to 50 per cent of their crop," he said. "This is thought to be associated with the loss of Elvaron Multi (a fungicide), which had acaricidal properties, and the fact that new varieties are more susceptible to the disease."

In a commercial survey he found that blackberry mite numbers were small and they did not relate to the crop damage score made by the growers concerned. To determine the best spray control he carried out an acaricide efficacy trial on four blackberry varieties - Loch Tay, Carmel, Chester and Loch Ness. The products involved were Headland sulphur, Codacide oil, Dynamec plus Break-Thru wetter and various mixtures of these products.

"The treatments performed equally well in reducing blackberry mite and red berry disease and increasing (marketable) yield," reported Cross. "Codacide oil looks the best choice as sulphur leaves an unsightly deposit and might be phytotoxic, so should not be used, especially during fruiting, and Dynamec is probably harmful to predatory mites."

Work on combating another serious pest, raspberry cane midge, was described by Adrian Harris. As eggs are laid in splits in the canes of primocane varieties, it paid growers to avoid damaging the cane, he advised. Unless the pest is well-controlled, infestation can result in cane death and thus reduced yield. At worst it can make raspberry production uneconomic.

Growers rely on chlorpyrifos for controlling the pest, but this is harmful to beneficials. Furthermore, being an organophosphate, it might not always be around. Consequently, the main reason for the project involves assessing the value of alternatives.

The products he tested were the new, more predator-friendly, neonicotinoids, Calypso, Centric and Gazelle against chlorpyrifos. He determined the number and timing of sprays necessary to achieve the best results. He noted that Gazelle had given good control of the midge in Polish trials.

In 2009, all of the insecticides proved effective when applied curatively six days after he had split the canes of the plants used for the trial. Sprays at half rate plus a silicone adjuvant were just as good. However, the treatments were ineffective when used preventatively six days before cane splitting, which led to almost immediate egg laying.

The result of a similar trial this year, without Centric, which is no longer approved for fruit crops, showed that spray timing is critical. The treatments worked well when applied a few days after cane splitting, although a threeor four-spray programme is needed for good control, maintained Harris. In commercial practice, pheromone traps are required to determine the best spray timing.

Although Phytoseiulus persimilis can control red spider mite in protected strawberries and raspberries very well, it has shortcomings. A project to find out whether any native predatory mites could back it up has been carried out by ADAS entomologist Mike Lole with some "interesting" results.

"Phytoseiulus is a tropical mite and does not survive our winters, may fail at low temperatures and can be costly," he said. "But there are native Phytoseiid mites that may be beneficial."

To identify these mites a number of ADAS consultants collected 55 soft fruit crop foliage samples, mostly strawberries and raspberries, from 32 farms in 18 counties. Lole examined the samples to see what mites they harboured. He found only five species, including Amblyseius californicus (only on strawberry foliage), which is not native and therefore cannot be released in outdoor crops. Most of the mites on raspberries were A. andersoni.

Lole said he was surprised to find the Typhlodromid mite because it commonly inhabits apple orchards. He pointed out that A. californicus and A. andersoni are mass-reared in the UK.

Weed control in bed-grown strawberries is never easy, partly because some weeds develop resistance to the dwindling number of approved herbicides. That is why the HDC commissioned ADAS soft fruit specialist John Atwood to evaluate the herbicides used for a range of purposes in the crop.

The first herbicides that Atwood examined were residuals for use on pathways between beds, where groundsel, willowherb, annual meadow grass, sow thistle, redshank and black nightshade predominate.

"Overall the best and longest-lasting control was given by Chikara, a sulfonylurea, but it's not got approval for strawberries and so there's a need to get a SOLA (specific off-label approval) for it," he said. "Springbok, a winter oilseed rape herbicide, also did well. One problem with Sencorex, which also gave good results, is groundsel resistance."

Of the post-planting contact products assessed, Springbok, Teridox and Goltix plus Alpha phenmediphan induced leaf distortion, while Goltix at 5l/ha caused only slight leaf scorch and stunting but was safe at 3l/ha, explained Atwood. Dual Gold, Alpha phenmediphan and Dow Shield were also safe.

"The fruit was tested for residues of Goltix and Dual Gold but none were found," he said. "There's a new SOLA for Dual Gold and one is under consideration for a wider application window for Goltix (currently it can only be used from September onwards)."

Atwood explained that the use of Shark as a contact treatment for runner and weed control along the pathways or alleys was brought about by the loss of paraquat. However, it proved ineffective for runner control, though with the addition of Harvest its activity was improved. Harvest at 5l/ha gave the best results, but Reglone was only partially effective against both runners and weeds.

Shark was also tested as a winter clean-up treatment on beds and matted rows at two rates and three timings. There was little difference in the appearance of the plants between the December (just dormant) and 4 April (early growth) treatments. There was also no difference in the appearance of the flowers in the high-rate (0.33l/ha) April treated and untreated control.

Shark currently only has approval for use before planting strawberries, nor can it be applied to pathways or to the crop itself, explained Atwood. However, the HDC hopes to get a SOLA for its use on the crop, he said.

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