Monitoring at-risk crops for aphids needs to be done until winter conditions take hold, growers are being advised.
Thanks to the mild conditions, aphids are likely to be multiplying and moving on the ground in autumn-sown crops, especially in more southerly areas where they were not fully controlled before flights ended.
As a result, the risk of spread of barley yellow dwarf virus (BYDV) and turnip yellows virus (TuYV) is likely to be high, warns AHDB Cereals and Oilseeds.
The exceptionally mild weather, which most areas have been experiencing throughout late November and early December, has led to some late aphid flight activity at Wye (Kent) and Starcross (Devon) being reported but there is not much elsewhere.
In the far South, there is a small chance of winged aphids still arriving from outside crops. Activity on the ground will continue until temperatures drop, with development and reproduction possible down to 3-4degC and walking between plants still possible above 1degC.
AHDB says it is hard to be precise about the level of frost needed to deliver a knock-out blow to aphids, but three to five consecutive days with temperatures dropping below -6degC should cause high mortality.