Prolonged wet conditions in many parts of the country mean that winter spray programmes are behind schedule and time is running out for some applications.
"Snow and cold pose a number of issues for anyone looking to spray," said initiative manager Patrick Goldsworthy. "Melting snow is likely to result in saturated soils.
"This may lead to recently applied pesticides being lost in run-off or field drainage. The risk of run-off will be worse where ground is frozen. Best practice is to not spray frozen or water-logged soils until field drains have stopped running."
Catchment Sensitive Farming's Steven Bailey added: "The temptation is to take advantage of the good travelling conditions offered by frozen ground.
"The downside is that if heavy rain falls before a thaw, the risk of run-off is very high. Spraying in such conditions poses a significant risk of pesticides reaching water as well as potential crop damage."
Best practice is being promoted by the Voluntary Initiative and the Crop Protection Association in partnership with the England Catchment Sensitive Farming Delivery Initiative.
Further advice is available in the Voluntary Initiative booklet H2OK? Water Protection Advice, available at www.voluntaryinitiative.org.uk.