WHILE WARM conditions may have lead to good crop establishment and growth, growers need to beware of the increased aphid risk in mild weather, ADAS has warned.

Aphid development is affected by temperature and an accumulation of “day degrees” above 3 ºC from the date of crop emergence can be used as a guide to predict optimum spray timings, explained ADAS consultant Susan Twining.

The number of day degrees can be calculated by subtracting 3 ºC from the daily mean temperature, she said.

“Updated guidelines indicate that secondary spread of aphids and BYDV can occur when 170 day degrees have been accumulated.”

With mean temperatures around 14-15 ºC, early September sown crops could benefit from aphicide treatment towards the end of September if aphid infestations become obvious and start to show signs of increasing, she said.

“Crops that have been treated with imidacloprid-based seed treatment (Baytan Secur, Raxil Secur or Sibutol Secur) should be protected for around six weeks, although a shorter protection period is likely if crops are drilled at very low seed rates.”