8 September 1995

Autumns time for adjuvants

ADJUVANTS – spray additives – have a useful, albeit limited, role to play in autumn herbicide treatments.

For some time, adjuvants have been advised to maximise the effect of some graminicides in oilseed rape. Fusilade (fluazifop-P-butyl), for example, requires Agral, and Actipron must be added to Laser (cycloxidim). Pilot (quizalofop-ethyl) also needs a suitable adjuvant oil.

More recently, adjuvants have been included in label advice for Cibas new cereal weed-killers based on clodinafop-propargyl, namely Topik (straight clodinafop), Amazon (clodinafop + diflufenican) and Hawk (clodinafop + trifluralin).

"Weve tested additives ever since we started developing clodinafop," says the firms Andy Pigott, who points out that the labels include named adjuvants such as Adder, Agral, Galion and Li700. "Our preference is for mineral oil. This gives the most robust control across the range of easy- to-kill to difficult blackgrass."

One problem, he says, is that the UK market for adjuvants is very complex. With big differences in performance users need to choose with care, he warns.

The ways in which different materials alter the results are still not fully understood. But work at Silsoe Research Institute confirms Mr Pigotts view.

Dr Paul Miller has just completed the first year of a MAFF-funded study to examine their effects. "We tried six different types of adjuvant to see if they made any difference to spray quality and droplet structure," he says. None are marketed as anti-drift materials but solely as pesticide enhancers, he notes. "The surprise was that we got much bigger differences than we expected."

Droplet size effect

The experiments, based on droplet size and velocity measurements of sprays from flat fan nozzles, are still only in their initial stages, stresses Dr Miller. But the clear message is that product selection could have a drastic effect on the performance of the sprays active ingredients, particularly where drop size is critical.

"Were not talking about a mere tinkering exercise," he comments. The work suggests some products can easily shift spray quality from fine to medium. Others may render medium quality output coarse, he warns.