5 April 1996

Adjuvant reaches the parts others cant

AN adjuvant with good spreading power said to allow pesticides to reach previously hidden areas has been launched.

Newman Agrochemicals claims its Silwet L-77 is the first organosilicone additive authorised for use with fungicides. The product lowers the surface tension of spray solutions to spread pesticides 25 times further than other non-ionic wetters, it says.

More than 50 independent UK cereal trials in the past five years show its use has consistently boosted disease control compared to using fungicides alone, it adds.

Yield increases averaging 0.3t/ha (2.4cwt/acre) represent a six-fold return on the cost of the adjuvant, according to technical manager David Foster.

Newman says the new adjuvant eases fungicide flow between leaf sheath and stem, potentially improving eyespot control. It also helps sprays penetrate deeper into canopies to reach untouched inoculum of mildew and septoria, making it "ideal" for treatments from first node to flag leaf (GS31 to 39).

The product performed especially well in trials under severe Septoria tritici pressure at the University of Wales, Aberystwyth.

Crop science lecturer Malcolm Leitch says its ability to provide "thorough coverage of the complete leaf" was particularly valuable to the protectant component of a fungicide programme based on Impact Excel (chlorothalonil/ flutriafol).

Flag leaves in unsprayed plots had 100% septoria by July 6 and the yield was 6.3t/ha (2.5t/acre). Full-rate fungicide plus the adjuvant gave 2.3t/ha (18cwt/acre) more. Even at half-rate Impact Excel the Silwet boosted yields by 9% or 0.67t/ha (5cwt/acre) over the same dose of fungicide used alone, reports Mr Leitch.

He believes the adjuvants super wetting properties may have helped the sprays to enter the leaf stomata. "This would be particularly useful for the systemically-acting component of the fungicide," he comments.

Despite such results Mr Foster urges care in choosing spray additives. "There may be components of a tank mix which wont benefit from the adjuvants mode of action."

lInteragros Slippa, launched last autumn, contains the same basic organosilicone as Silwet L-77, says the firms Richard Newman. But the formulation is slightly different to counter wash-off. &#42

Silwet L-77 gives a thorough coverage of the complete leaf, says University of Wales crop science lecturer Malcolm Leitch.