Seed treatments well worth a look

Failure to use neonicotinoid seed treatments on high pest pressure sites can result in near total crop failure (centre).

After early-season aphid pressure, specialist insecticide seed treatments look set to prove their worth in minimising virus yellows damage to sugar beet.

And the latest products clearly helped crops establish in tricky conditions last spring.

The relatively mild winter encouraged aphids to build up on over-wintering hosts, says crop protection specialist Alan Dewar. The unusually warm April then stimulated them to move into beet crops from oilseed rape and brassicas much earlier than normal.

"Around 1.5% of the winged migrants were carrying beet mild yellowing virus," says Dr Dewar. "And with up to 10 aphids on each plant, we can expect primary infection with virus yellows, even in Cruiser Force or Poncho Beta-treated crops, to be about 10-15%.

"In previous years we've not seen Cruiser Force or Poncho Beta-treated crops with more than 5% infection, but this early pressure has been unprecedented. Over nearly 25 years of research, I've never seen as many winged aphids in the crop."

While the full impact will not emerge until the end of August, Dr Dewar expects untreated crops to have up to 70% of plants infected, causing significant yield losses.

"We're expecting it to be a bad year universally for virus yellows and even treated crops will have some infection. However, seed treatments will have considerably reduced infections compared with untreated crops, or where growers relied upon foliar sprays."

Growers who relied on granular treatments in high risk Docking Disorder areas can expect to see heavy virus yellows, he adds.

"In future, these growers should really think about combining a granular treatment with a seed treatment."

In terms of product efficacy there is little to choose between Poncho Beta and Cruiser Force when it comes to aphid control, says Dr Dewar.

But this year's trials suggest the latter controls larger pests, such as millipedes and wireworms, better.

"Three out of six trial sites have shown soil pest damage, despite the dry April conditions reducing pest pressure.

"At Whittlesford, Cambridgeshire, where wireworm pressure was intense, Cruiser Force has provided a higher plant population than Poncho Beta.

"It's a similar story against millipedes and symphylids on fen soils at Baston in Lincolnshire, where Cruiser Force has given about 5% more plants in treated plots.

"The tefluthrin component of Cruiser Force is proving a better soil pesticide against these larger pests."

Product persistence has been good, Dr Dewar confirms. Despite the dry April, soil insecticides kicked-in after the first decent rain and were still giving benefits 8-10 weeks later with the crop at the eight-leaf stage.

"In late June we were still seeing plant kill due to millipede pressure in untreated crops."

Independent agronomist Bob Simons describes the Baston Fen site as particularly "nasty" when it comes to establishing crops, flat millipedes being the main problem. "You can't split the two treatments on aphid control, though it seems tefluthrin just has the edge in difficult pest situations.

"But the key message is that all products have really delivered in what has been a difficult year."

Cruiser Force was available at a small premium over Poncho Beta on a limited range of varieties last year, notes the AICC's Pat Turnbull. "Both treatments offer very similar, good and persistent activity on foliar pests.

"This season, in parts of Norfolk, where insecticide seed treatments were not used, we've seen high levels of damage from capsids and/or thrips causing multi-crowning due to their feeding on seedlings."

Aphid control

The use of insecticide seed treatments on top of granular treatments at Docking Disorder sites to improve early aphid control and control other foliar pests is well worth considering, adds Dr Turnbull.

There were effectively two emergence periods this season, says Broom's Barn's Mike May - early April when soils were still moist below the surface and May after the rains.

"In both situations emergence was surprisingly good, ie where only part of the field emerged early, virtually all the rest came through about eight weeks later after the rain.

"In fields treated with Poncho Beta, Cruiser Force (or Gaucho, some was being used up from 2006) there have been very few problems."

Most issues have been on the 15% of the beet area where such seed treatments were omitted, he says. "These have caused many more headaches than in the whole of the rest of the crop."

andrew.blake@rbi.co.uk