Need for aphicides increased by the Indian summer
WINTER cereals emerging as late as last weekend may need an aphicide treatment to prevent barley yellow dwarf virus taking hold, warns ADAS. And early crops already treated may need a second spray to avoid late infection.
"Normally we have a wet, windy spell at the end of this month which stops aphids flying into crops," says entomologist Jon Oakley. "But we are still seeing a few winged aphids in areas which have enjoyed an Indian summer."
Growers in those areas should consider spraying even recently-emerged crops, he says. Usually, plants emerging after mid-October are considered safe. Crops can be sprayed as early as the two-leaf stage, but can be left to five leaves to suit herbicide applications.
Crops sprayed more than two weeks ago may need treating again within the next fortnight, adds Mr Oakley. "The spray does not protect new foliage."
Growers may need to look hard. "Aphids can be difficult to find. I would want to be sure I hadnt got them before deciding not to spray, especially in sheltered areas."
Arthur Marshall of Woodford Farm Services, Plympton, Devon, has seen more aphids this year than ever.
Near the coast, he is using a three-spray programme to contain the pests. Many crops have been treated once, with a second spray due this week. A top-up will be needed at the end of the month.
"Crops came up very fast this year. Normally, 20% of the crops dont need spraying. But everything looks as though it has been early-drilled. It is still growing strongly, so spray is being diluted as soon as its applied. And aphid migration looks like it will go on and on. We are certainly not going down the low input road. Cypermethrin costs 55p/acre, but the crop is worth £300."
Peter Taylor, of Bishops Stortford-based Samco, does not consider his area to be at high risk. But he has more aphids than usual, and reckons some 10% of crops will be sprayed twice. "We sprayed some sheltered, early-emerged, lush crops early on as cheap insurance."
In a normal year he advises growers to spray crops emerging before the end of October as routine. But this season, crops drilled after sugar beet and potatoes may also be at risk. "If it stays mild, crops coming up in November will need treating. But if it turns cold and we get below average day temperatures, they will be OK."