High levels of barley yellow dwarf virus (BYDV) have been seen in cereals this year, which should encourage growers to reconsider their seed treatment options for 2012 plantings.

The most likely cause is the extraordinary conditions seen in the South West during January, which allowed the flight and migration of the aphid virus vector, says Jonathan Blake at ADAS.

“Unless the crop was sown very late, seed dressings would have made very little difference to infection of BYDV. However, it will have focused people’s minds on the threat.”

Richard Harrington, head of the Rothamsted Research insect survey, says that although it is far too early to predict next autumn’s aphid levels, a mild and moist summer could allow levels to build in wild grasses.

“With the right conditions they can multiply and spread to the new crop, but the best advice is to keep an eye on forecasts, which should prompt growers to check crops for aphid numbers. In high-risk areas, seed treatments would make sense,” says Dr Harrington.

Consequently, insecticide seed treatment could prove to be popular for the coming drilling season, with Deter and Tripod Plus being the two products with activity on aphids.

“We have always treated with Deter where there is a perceived threat, however, we have seen huge amounts of BYDV infection this year in both wheat and barley,” says Stephen Harrison, AICC agronomist in the South West.

“We will be increasing our Deter-treated area to about 50-60% from the 40-50% that it has been in recent years.

“Late-drilled crops after maize or grass would not pose a problem, but I will be using a wider definition of what is ‘at risk’ when considering the rest of my cereal area,” adds Mr Harrison.

With the extra cost of £90-100/t for the addition of Deter to seed, combined with dressing for seed-borne and foliar diseases, could result in seed costs of up to £500/t. However, Mr Harrison believes the investment is worth it with grain prices remaining strong.

“It has been shown there is a yield response with Deter in any situation, as it has some activity on slugs and other pests such as flea beetles.

“A well-timed pyrethroid spray will still be necessary though, and growers should be prepared to follow up with further applications where you get the secondary infection we have seen this year,” he points out.

The focus this autumn, along with BYDV, should be on the seed-borne diseases and take-all, which have the most serious threat to establishment and crop growth, says Mr Blake.

“Bunts and seedling blights should be covered by a standard, single-purpose seed dressing, along with smuts, but they are rare. Growers continually sowing home-saved seed will be particularly at risk,” he points out.

Mr Harrison is committed to encourage testing on all seed, which is best practice when considering what seed dressing, if any, is required. “If you find out what pathogens are present on the seed, you can make an informed decision and, in some cases, we won’t treat the seed whatsoever,” he says.

Yellow rust

Along with the incidence of virus infection being high this year, yellow rust was also evident in wheat crops following the mild conditions during the winter months. “It cycles extremely quickly,” says Mr Blake.

“Therefore, it can diminish final yields even at the early stages of crop growth, which makes it the most serious pathogen to consider in the autumn and spring.”

Mr Blake believes that a yellow rust active seed treatment is necessary where susceptible varieties such as Oakley or Torch are grown. “In a normal year where fungicide programmes run smoothly with correct timings, there wouldn’t be a huge benefit.

“However, in a season such as this, it will take some pressure off the spring fungicide programme and also give some peace of mind through the winter,” he explains.

Supply

There have been concerns over the availability of aphid-active seed dressings with the increased demand.

“Use of Galamo to protect against yellow rust will also increase, with many more planted varieties susceptible to the pathogen, but there will be more of both products available than previous years,” says Bayer CropScience product manager Peter Stacey.

“We have anticipated the extra demand for Deter and Galmano by communicating with distributors and we are hopeful there will be enough to meet the extra demand.”