Justin time for this autumn Bayer CropSciences insecticide Biscaya (thiacloprid)has gained an extension of use for the control of the main vector of turnipyellows virus in oilseed rape: the peachpotato aphid.
Yieldloss to TuYV is commonly in the order of 10-15% but can be as much as 30% in ahigh pressure year. Infections in September and October have the greatestimpact on yield. This is the time when peachpotato aphids are migrating fromweeds and summer host crops lettuce, potatoes and vegetable brassicas tooilseed rape as their winter host.
Followingthe EU restrictions on certain neonicotinoid seed treatments, which gave six toeight weeks activity against these aphids, growers next line of defence isfoliar insecticides. Bayer campaign manager for insecticides Neil Thompson saysthat Biscayas extension of use bolsters their armoury to three. Growers nowhave a fighting chance but success will depend on the duration of aphidmigration and how these foliar insecticides are deployed.
Biscayais the fastest acting insecticide to stop aphids feeding and to kill them so itis the logical first spray choice. Should aphid fly-in continue beyond its twoweeks activity a second spray will be needed. Flonicamid and pymetrozine arethe two options and both offer alternative modes of action to Biscaya.
BBROlead scientist Dr Mark Stevens, who led the body of research that our currentunderstanding of TuYV comes from, supports this approach. He says; From recentexperience of foliar insecticide options on sugar beet in BBRO trials, Biscayais the most effective product for quick knockdown and to reduce virustransmission.
DrStevens also emphasises the importance of crop monitoring. RIS 10-year mean trapping data shows that peachpotatoaphids can be active from emergence of OSR crops in early to mid-Septemberright through to the end of November. However, Dr Stevens points out that thismasks considerable seasonal and regional variation.
They may be active throughout this period, for partof it with occasional peaks, or be almost entirely absent. This means thatcontrol strategies may need to tackle sustained aphid pressure, some blips ofpressure or virtually none at all. Monitoring from emergence into early winter is therefore vital. Ideallyuse local yellow water traps and keep a close watch on AHDB aphid news.
As there is not yet a treatment threshold forpeachpotato aphids in OSR Dr Stevens says all growers can do this autumn is toconsider those that apply for similar virus threats in other crops. “Forexample the threshold in sugar beet at early growth stages for foliar aphicideapplication is one green wingless aphid per four plants.
For some, this threshold may appear to be low, but itis also important to remember that, in recent years, up to 30% of aphids havebeen found to be carrying TuYV. And if you have already applied a pyrethroid tocontrol cabbage stem flea beetle, it will also have had an impact on some ofthe beneficial insects that predate on aphids. In the future however, an OSRspecific threshold is needed for growers to implement proper IPMstrategies.”
Biscayasextension of use means it can now be used twice on a crop of winter oilseedrape at 0.3 L/Ha; once in the autumn to control aphids and once in the springto control pollen beetle. Conscious also of the increased risk of cabbage stemflea beetle damage to OSR following the neonicotinoids restriction Mr Thompsonadds;
We have not carried out any trials looking at Biscayaon cabbage stem flea beetle. Based on our knowledge of the pest spectrumof thiacloprid, there may be some level of efficacy against adults which arepresent at the time when Biscaya is being applied, however this wont be a usesupported by Bayer CropScience.