Despite low aphid counts so far this year, cereal and oilseed rape aphid populations may increase following the recent rain, particularly if an Indian summer develops. This is just when young winter oilseed rape crops are at their most vulnerable, growers are being advised.
As potato harvesting gets underway and aphids move on to other food sources, growers are being warned by experts to be on their guard against against a potential aphid threat, although SRUC entomologist Andy Evans says burning-off of potato crops’ haulm can help to keep aphid populations down, as does not give as them time to adapt their physiology to changing circumstances and move on.
If aphids do move into winter oilseed rape seed, control could be challenging. This is because crops will not have the safeguard of neonicotinoid seed treatments to protect them from aphids and the aphid-transmitted turnip yellows virus (TuYV), unless planted in areas where emergency approval for their use has been granted. In addition, there is resistance in peach-potato aphid populations to the pyrethroids now used for protection from flea beetle.
Dr Evans reminds growers to keep their eyes on the ground and use the suction trap network data for their local area to check whether the peach-potato aphid is present. Although so far this year flights of these aphids are quite low, higher than average numbers have been caught in suction traps and water traps this season. This aphid can cause up to 30 per cent yield loss in oilseed rape through transmission of TuYV to the vulnerable seedlings.
“If we now have a cold spell, it will knock the aphids dead but if we get warm, settled weather, action may be needed if aphids fly into crops.”
He advises growers to check on the leaves (including the underside of the leaves) and if aphid colonies are present there are two main options available to reduce the threat from TuYV: pymetrozine at 0.3 kg/ha; thiacloprid at 0.3 l/ha.