Rigid pgr programme key for first-time strob users
Rigid pgr programme key for first-time strob users
FIRST-TIME strobilurin users on wheat could be disappointed unless they adopt a robust growth regulator programme, says a Warks-based agronomist.
"If there was one over-riding message from last year, it was do not overlook late growth regulators if you are applying strobilurin fungicides," says Profarmas Peter Dews.
"Last season many crops which had received strobs grew big green canopies with a lot of leaf which held the rain. When the wind came three weeks before harvest they became top-heavy and down they went. Lodging was particularly noticeable in Rialto, a relatively tall variety."
About a fifth of the wheats in Mr Dews heavyland area received the novel fungicides in 1998. But with the new materials ability to boost yields and increased interest in their role as an anti-drought measure on lighter land, overall use could rise to 40% this year, he believes.
With catchy weather setting in during crucial early stem extension spray timings, the need for a late growth regulator could be stronger this season, he believes. "If people have missed that first application the later one will be even more vital."
Compared with barley, where crop height and the shortening effect of late regulators are normally more important, few wheats, until now, have merited such treatment. "It varies each year according to variety and field aspect, but it has only ever been 10% max." That figure may need to change if the full benefits of strobilurins are to be realised.
Best straw shortening should come from an application of products containing 2-chloroethylphosphonic acid, for example Terpal (2-ca + mepiquat chloride), Strate (2-ca + chlormequat) or Satellite (2-ca + choline chloride + imazaquin). Applications should be between third node (GS33) and early flag leaf, Mr Dews advises.
Depending on when the first strobilurin was applied, the pgr treatment could coincide with an early flag leaf spray, though a separate application may be required for maximum effect.
The optimum timing is between second node detectable (GS32) and flag leaf collar visible (GS39), he advises.
The latest timing in wheat is when the boots are swollen (GS45) or the flag leaf sheath opens. In barley it is before the awns are visible. "But at these later timings lodging control can be less effective."
Dose depends on previous applications and timings, crop variety and field/site fertility. But it should not be less than 1 litre/ha for Strate and Terpal or half rate, ie 2ha/pack, for Satellite. "When using Terpal a recommended ethylene oxide adjuvant such as Agral or Nion should be added at 40ml/100 litres of spray solution."
Only where the crop is clearly under stress is more caution justified. "Late growth regulation can damage crops in dry weather. But growers using strobilurins in their fungicide programmes should definitely consider a late pgr to avoid the problems of last year." *
STROBS AND PGRS
• Lush lodging-prone wheats.
• Late regulator sprays useful.
• Optimum timing GS32-39.
• Dry weather reservations.