Winged peach potato aphids are moving into oilseed rape crops and growers should treat the pest before it spreads turnip yellows virus (TuYV).
HGCA-funded monitoring work carried out by Rothamsted Research estimates that 70% of UK peach potato aphids – or Myzus persicae – carry TuYV.
Left untreated, the same project has estimated that the disease could cost the industry about £50m each year from lost yield in excess of 200,000t.
As with cabbage stem flea beetles, without neonicotinoid insecticide seed treatments rape crops have been left unprotected against Myzus this autumn.
Independent entomologist Alan Dewar says winged myzus aren’t difficult to find in parts of East Anglia, but it’s their wingless progeny that alerts to the risk of virus spread when found in the crop.
“When a virus-infected winged aphid lands and feeds it takes up to three weeks for enough virus to build up in the newly infected plant to pass it on to feeding offspring.
“So if you only have winged aphids, you still have some time to spare before secondary infection will occur. If there are plump, wingless aphids present they’ve been there a week or so and need treating immediately,” says Dr Dewar.
Trapping at Syngenta’s Innovation Centre’s and monitoring of brassica vegetable crops by their field technical managers has also detected the movement of winged myzus.
Turnip yellows virus containing tips
- Monitor Rothamsted Research aphid alerts and crops to substantiate risk
- Treat as soon as wingless aphids detected in crop
- Two products now approved – Plenum and Tepekki
- Use methylated seed oil with insecticide to improve control
The company’s Simon Roberts says growers must take heed of these early warnings and be ready to treat as soon as infestations are found in their crops.
“It’s important to get the application timing as precise as possible to prevent focci of virus developing in the crop from the feeding activity of infected aphids, which could then spread further as the season progresses,” he adds.
Widespread resistance is present in populations of myzus to both pyrethroids and pirimicarb, leaving growers with limited options for control of the pest.
It was feared Syngenta’s Plenum (pymetrazone) would be the only effective product available this autumn and as it can only be applied once and gives two weeks protection, timing is crucial.
However, an emergency approval has been granted for Belchim’s Teppeki (flonicamid) this autumn, taking the pressure off growers’ decision on when to spray. The product also has no resistance issues.
“If it stays mild until the end of October and aphids continue to move, then you will need more than one spray, so it allows you to alternate,” says Dr Dewar. “In my trials Plenum with an oil has shown the best results, but both will do a job.”
Mr Roberts explains that aphids stop feeding almost immediately after ingesting Plenum once it has been applied to the crop.
“Although they may remain alive on the plant for up to four days, they pose no further risk of virus spread,” he adds.
Belchim’s development and marketing manager Simon Leak explains that Teppeki works in a similar way, by stopping aphids feeding and growers won’t see the knockdown effect provided by some insecticides.
“Don’t expect to see dead aphids, but if you look through a hand lens you will see that they have stopped feeding and will seem disorientated,” he adds. “They then die from dehydration or starvation.”
Both products are systemic and translaminar, so will control aphids feeding on the underside of leaves where they may not have come into contact with the spray and both give about two weeks protection against the pest.
Mr Leak says adding methylated seed oil to Teppeki will also improve product penetration and coverage of the target.
“It’s applied at 100g/ha with a water rate of 200 litres/ha, although in a denser crop a higher water rate could required. It can be applied up to eight true leaves or 11 December this year,” he adds.
Bayer CropScience reports that it is waiting for an extension of use for its foliar insecticide Biscaya (thiacloprid) to control myzus in oilseed rape. The company anticipates getting approval just in time for growers looking to control the pest this autumn.
Brian Ross, technical manager at Frontier, welcomes the peace of mind more product choice will provide, but reminds growers that they should still remain vigilant and only spray where necessary.
“It’s a case of keeping an eye on Rothamsted Research aphid alerts and getting on your hands and knees and looking for aphids as the risk rises.
“We just hope that some cold weather arrives and helps slow the aphids down,” adds Mr Ross.