12 March 1999

Fine-tune may be needed for strob-treated crops

By Andrew Swallow

NITROGEN, pgr and seed rates could all need changing for strobilurin treated crops, says manufacturer BASF.

Raising N rates is one suggestion. Field trials show that nitrogen response curves are altered by Landmark (kresoxim-methyl + epoxiconazole). Research in the firms German laboratories shows increased activity of the nitrogen assimilation enzyme, nitrate reductase.

But business development manager Steve Waterhouse urges caution. "We can generate more yield by applying more nitrogen to kresoxim treated crops, but reduced amounts of nitrogen could boost margins, too.

"Less nitrogen is left in the soil after harvest, which has to be a good thing environmentally," he adds. But distributor Crop Cares agronomy specialist Neal Boughton points out that may not be so popular on farm.

"Two years ago where we had oilseed rape following a field of strob trials you could see a distinct difference in establishment where strobs had been used.

"Such differences may not go through to yield of the following crop, but growers will notice it, and it could allow pigeons in."

Plant growth regulator management also needs attention. "Higher potential yields mean higher risk of lodging," says Mr Waterhouse.

But he counters suggestions that kresoxim-methyl treatments increase lodging more than Amistar (azoxystrobin). "Across seventeen trials and two years we have not seen a difference."

Mr Boughton echoes the importance of pgrs. "The strobs produce a heavy ear on a green, more flexible and more pliable stem. I think that both strobilurins can make crops more susceptible to lodging."

Any antagonism of kresoxim-methyl with ethylene promoting pgr Terpal (ethephon) is dismissed by Mr Waterhouse.

The persistent greening effect means lower leaves can contribute more to grain fill. Such canopy modifying effects must have implications on optimum seed rates and sowing dates, he suggests.

But green straw can cause harvest problems, and will be investigated in field trials this summer, says Mr Boughton. "In some crops last year the grain was fit at 15%, but the straw was still 50%. The combine just could not separate them."

lBASF assures growers of adequate kresoxim-methyl supplies in time for T1. It expects to take at least half the strobilurin market, which the company puts at 25-30% of all cereal fungicides. A small Europe-wide price increase is forecast, but that will be less than 5% in the UK.

STROB POINTERS

&#8226 N optimum more flexible and higher?

&#8226 Less residual N available for following crops.

&#8226 More pgr required.

&#8226 Lower seed rates possible.

&#8226 Strob/Terpal antagonism dismissed.