28 March 1997

Spring PGRs in question on bone-dry cereal soils

By Andrew Blake

EXCEPTIONALLY dry soils raise question-marks about cereal growth regulators this spring.

Soils in parts of the east are already twice as dry as they were this time last year. This means crops may no longer merit early chlormequat, says ADASs John Garstang.

"The longer we go into spring with dry soil conditions the less pressure there will be to apply early PGRs as insurance." Indeed unnecessary treatment could create unwanted tillers and tax crops grain-filling capacity if the weather stays dry, he adds.

Sustained dry weather will also reduce the need for late PGRs, says Mr Garstang. But if it turns wet and crops become tall and lush from GS33 (third node), products like Moddus, Terpal and Upgrade can be relied on to shorten upper internodes.

In some dry years crops getting only early-season chlormequat have ended up taller than their untreated counterparts, he notes.

ADAS advice is to apply first split PGR at late tillering, or use a single treatment if weather or other field work delays application. But the need to spray crops at marginal lodging risk needs reassessing.

Growth regulator manufacturers take a different line. With chlormequat about 10% cheaper than it was last spring, the case for using it now remains strong, they maintain.

"Late treatments tend to be more expensive and can be more aggressive on crops," says BASFs Martin Lainsbury.

The down side of delaying is that growers may lose the benefits of better rooting, suggests colleague Tony Grayburn who confirms the drop in chlormequat price.

Novartis product manager Andrew Cottrell accepts that in the current dry conditions widespread need for chlormequat will be less than in 1996. "But I still believe there are plenty of crops that are extending rapidly, getting lush and need checking."

Adopting a wait and see approach risks losing the shortening effect on lower plant internodes which cannot be offset by later checks on upper internodes, he maintains. "You need to ensure the base of the plant is strong."

Main timing for the firms Moddus (trinexapac-ethyl), most often recommended as a half-rate mix with chlormequat, is GS30-32 (ear at 1cm to second node), he says.

Herts-based AICC member Jamie Mackay of SAMCO says that in theory the need for chlormequat is lower than normal this dry spring. "But in practice we are already going on with weed-killers and fungicides and you dont leave it out. The last thing my clients want is for me to save a few pounds and then have their crops go flat." With most crops already at GS30 the risk of encouraging unwanted tillers is relatively small, he believes.


&#8226 Very dry soils in east.

&#8226 Early regulator less justified?

&#8226 Risk of unwanted tillers.

&#8226 Later PGR safety net.

&#8226 Lower internode the key.

&#8226 Early treatment cheap insurance.

&#8226 Chlormequat price down.