Syngenta's Plenum insecticide knocks out aphid resistance threat in oilseed rape

Oilseed rape growers now have an effective option to control late aphid infestations and minimise the risk of yield-robbing Turnip Yellows virus this autumn, with a new approval for the novel resistance beating insecticide treatment, PLENUM.

The autumn application option will be especially welcome with the increasing numbers of the most virulent virus spreading aphid, Myzus persicae, that are resistant to all other autumn foliar insecticides in OSR. Early season reports of aphid activity this year, issued by Rothamsted Research and the HGCA, have revealed that 96% of Myzus tested were resistant to pirimicarb and 94% resistant to pyrethroids – the mainstay of growers’ autumn insecticide strategies.

Syngenta OSR Technical Manager, Chris Charnock, advocated that where aphid populations build up later in the season, PLENUM is the perfect complement to current seed treatments to extend control of all aphid species through the autumn.

He warned that Turnip Yellows virus (TuYV) is spread by aphids feeding on an infected plant, and then moving onto an uninfected plant to continue feeding; greater aphid activity in the crop results in faster and more widespread infection. TuYV has typically resulted in yield losses of 0.5-0.75 t/ha in UK commercial crops, although up to 1.5 t/ha reductions have been shown in trials.

“PLENUM stops the feeding activity of all aphids feeding on treated plants within an hour,” he advised. “Although treated aphids may stay alive for up to 48-hours, any further feeding activity is stopped and the subsequent risk of virus spread prevented.”

Chris highlighted that PLENUM acts by both direct contact from the spray or the ingestion of sap from treated plants. The systemic activity within the plant means that any new aphids feeding will also be controlled, as well as further limiting aphid activity as the plants grow through the autumn.

Independent trials of PLENUM in OSR last year demonstrated an 80% reduction in aphid numbers three days after treatment in late October. Virus trials at Brooms Barn have also shown up to 70% reduction in the number of plants infected by TuYV with PLENUM treatment.

Experienced independent entomologist, Alan Dewar, who has trialed PLENUM for the past three years, reported that in some years overwhelming numbers of aphids can infect a large proportion of plants by primary infection; in most years, however, secondary spread from primary foci of infection is what causes the yield loss.

“Good timely control of aphid results is a reduction in TuYV infection, with concomitant potential increases in yield in years when virus incidence is high,” he added.
Chris Charnock advised autumn PLENUM applications should be made as soon as Myzus activity is seen in the crop, at 0.3 kg/ha when used alone, or 0.2 kg when used in conjunction with a recommended methylated rapeseed oil.

The new approval now allows for PLENUM to be used once in the autumn to counter the aphid threat, and again as a pre-flowering application in the spring for Pollen Beetle control.