10 September 1999

PICK ADJUVANT FOR RIGHT MIX

CHOOSING the right adjuvant can make a big difference to autumn herbicide performance, especially where resistant black-grass is a concern, says John Haywood, technical manager with Intracrop.

But growers must remember that what may be a beneficial adjuvant with one herbicide can prove antagonistic to others in exactly the same conditions, he warns.

"A good example of this is putting mineral oil with Hawk," he explains. "That combination works well, but mineral oil is antagonistic with Lexus. So if these two herbicides are going to be used together in a tank-mix, the choice of adjuvant becomes critical."

The creation of a herbicide additive database by Intracrop should help growers with decisions this season and clarify tank-mix situations, he adds. "Each different adjuvant was tested with individual herbicides in order to create the data," he notes. "And different rates were also examined."

The database information can either be accessed via the Intracrop Adjuvant Helpline or by asking your distributor, continues Mr Haywood. "The information now exists, so growers should make good use of it. We can give very concise field-specific recommendations for a wide range of herbicide programmes. Theres no reason to get it wrong."

He stresses that adjuvants are designed to maximise herbicide performance and improve the control of moderately susceptible weeds. "Dont forget that certain adjuvants may work well with small weeds, but performance tails off quickly if applications get delayed."

He cites a trial looking at blackgrass resistance management which shows how even the performance of full rate herbicides can be boosted by the right adjuvant. Blackgrass control rose from 75% to 92% with the appropriate adjuvant, from a single herbicide application.

"This trial shows that an investment of between £2.50 and £5/ha in an adjuvant is worthwhile," he says.

Mr Haywood also points out that some formulations of the same herbicide do not respond to additives, depending on the dose used. "A good example of this is glyphosate. Sting does not respond to an adjuvant, so dont use one with it."

He concludes by putting growers minds at rest. "We know that adjuvants are considered to be a confusing area of agronomy. The database should help make decisions easier and maximise the weed control achieved."

The Intracrop Adjuvant Helpline can be contacted on 01969 640655. &#42

Control of blackgrass

Herbicide Herbicide + Herbicide + esterified Herbicide

alone mineral oil methylated seed oil + Galion

% control 75 79 87 92

Plants remaining a sq m 45 38 24 14