United Kingdom
September 26, 2014
Just in time for this autumn Bayer CropScience’s insecticide Biscaya (thiacloprid) has gained an extension of use for the control of the main vector of turnip yellows virus in oilseed rape: the peach–potato aphid.
Yield loss to TuYV is commonly in the order of 10-15% but can be as much as 30% in a high pressure year. Infections in September and October have the greatest impact on yield. This is the time when peach–potato aphids are migrating from weeds and summer host crops – lettuce, potatoes and vegetable brassicas – to oilseed rape as their winter host.
Turnip Yellow virus on OSRFollowing the EU restrictions on certain neonicotinoid seed treatments, which gave six to eight weeks activity against these aphids, growers’ next line of defence is foliar insecticides. Bayer campaign manager for insecticides Neil Thompson says that Biscaya’s extension of use bolsters their armoury to three. “Growers now have a fighting chance but success will depend on the duration of aphid migration and how these foliar insecticides are deployed.
“Biscaya is the fastest acting insecticide to stop aphids feeding and to kill them so it is the logical first spray choice. Should aphid fly-in continue beyond its two weeks activity a second spray will be needed. Flonicamid and pymetrozine are the two options and both offer alternative modes of action to Biscaya.”
BBRO lead scientist Dr Mark Stevens, who led the body of research that our current understanding of TuYV comes from, supports this approach. He says; “From recent experience of foliar insecticide options on sugar beet in BBRO trials, Biscaya is the most effective product for quick knockdown and to reduce virus transmission.”
Dr Stevens also emphasises the importance of crop monitoring. RIS 10-year mean trapping data shows that peach–potato aphids can be active from emergence of OSR crops in early to mid-September right through to the end of November. However, Dr Stevens points out that this masks considerable seasonal and regional variation.
“They may be active throughout this period, for part of it with occasional peaks, or be almost entirely absent. This means that control strategies may need to tackle sustained aphid pressure, some blips of pressure or virtually none at all. Monitoring from emergence into early winter is therefore vital. Ideally use local yellow water traps and keep a close watch on AHDB aphid news.”
As there is not yet a treatment threshold for peach–potato aphids in OSR Dr Stevens says all growers can do this autumn is to consider those that apply for similar virus threats in other crops. "For example the threshold in sugar beet at early growth stages for foliar aphicide application is one green wingless aphid per four plants.
“For some, this threshold may appear to be low, but it is also important to remember that, in recent years, up to 30% of aphids have been found to be carrying TuYV. And if you have already applied a pyrethroid to control cabbage stem flea beetle, it will also have had an impact on some of the beneficial insects that predate on aphids. In the future however, an OSR specific threshold is needed for growers to implement proper IPM strategies."
Biscaya’s extension of use means it can now be used twice on a crop of winter oilseed rape at 0.3 L/Ha; once in the autumn to control aphids and once in the spring to control pollen beetle. Conscious also of the increased risk of cabbage stem flea beetle damage to OSR following the neonicotinoids restriction Mr Thompson adds;
“We have not carried out any trials looking at Biscaya on cabbage stem flea beetle. Based on our knowledge of the pest spectrum of thiacloprid, there may be some level of efficacy against adults which are present at the time when Biscaya is being applied, however this won’t be a use supported by Bayer CropScience.”
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