5 February 1999

Growers need guidance through additives maze

A call for more

independent assessment

of spray additives was made

at last weeks meeting of

the Arable Research

Institutes Association.

Andrew Blake reports

HOME Grown Cereals Authority levy funds should be used to guide growers through the adjuvant maze, according to one supplier.

"In an era of reducing margins, the ability to get all the benefits of new chemicals at considerably reduced cost must be worth a further look," said Richard Newman, technical director of Interagro.

"Bemused, confused and almost inadequate," was how he described himself after a presentation by IACR-Long Ashton researchers on this complex issue.

Speakers included Dr Peter Holloway and Duncan Webb, who showed how the range of products in the Revised Adjuvants List 1998 affect spray characteristics and pesticide coverage, retention and uptake.

Videos of spray droplets bouncing across a leaf like ants and spreading to cover the surface gave delegates an insight into the detailed laboratory work involved. But to date MAFF funding has not allowed the studies to be pursued in the field, noted Dr Holloway.

For Mr Newman the key point was that adjuvants work. He likened them to the drive system of his car. "I have no idea what goes on under the bonnet. That is someone elses job. I know that if I turn the key it goes."

Pesticide manufacturers attitudes to adjuvants are clearly changing, he added. A frequent comment is that if pesticides needed adjuvants manufacturers would include them. "The facts do not bear that out."

When Cheetah (fenoxaprop-ethyl) herbicide was first launched the manufacturer was adamant that adjuvants were not required, he said. Within two years there was overwhelming evidence that a half dose with an appropriate adjuvant performed as well as the full dose alone. Earlier Weed Research Organisation work had shown similar potential with Roundup (glyphosate).

"Ignoring or rubbishing adjuvants wont make them go away. In todays economic and environmental climate pesticide manufacturers must accept that farmers will use them wherever possible."

Trials from several sources – including Morley Research Centre, the SAC and Ireland – more than make the case. In one instance adding Arma adjuvant to Alto (cyproconazole) fungicide boosted septoria control in wheat by 70%, he noted.

But exploring all potentially useful adjuvant/pesticide combinations is beyond the resources of firms like Interagro, hence his HGCA suggestion.

David Stock, AgrEvo formulations specialist, acknowledged that tank-mixing adjuvants could sometimes unlock products full potential. One reason for using them in the past was that commercial formulations had proved inadequate. "Some manufacturers made a dogs dinner of it. That is not the case any more. It costs £100m to get a new product to market so we have to get it right first time."

Other current reasons include use under what he described as "challenging" conditions, where active ingredients are potentially antagonistic, and where a dose cut is desirable for environmental purposes. Adjuvants can also assist where specialist all-in-one products are not justified by niche markets, said Dr Stock.

The main barrier to progress, emerging in ARIA discussions, appears to be manufacturers reluctance to identify more than a few select adjuvants to accompany their main products.

Mr Newman said 80% of all US pesticide labels include adjuvant recommendations. In the UK the picture is very different. "It is improving but it is slow."

"But why should we spend money to take away part of our market?" asked Dr Stock.

Gloucestershire farmer John Tingey said there was a strong desire for growers to know which adjuvants worked best with which products. "How do we find our way through this minefield?"

Long Ashton work on spray additives is confined to the laboratory, says Peter Holloway.

Would a spray additive help? The answer is not always straightforward. Adjuvant effects on spray quality

and interactions with leaf surfaces can have a big impact on results. Richard Newman (below) sees an increasing role for adjuvants.

SPRAY ADJUVANTS

&#8226 Additives coming of age.

&#8226 Actions better understood.

&#8226 Independent trials call.

&#8226 Registration loophole.

Data loophole under attack

A REGISTRATION loophole allowing adjuvant makers to avoid supplying residue data in the UK came under fire at the meeting.

Dr Stock said under present rules there was no requirement to provide such data if the adjuvant was recommended for use with half or less than half the approved rate of pesticide. "Where is the sense in that?"

The British Agrochemicals Associations view was that it would encourage adjuvant makers to avoid the authorisation process, he added.

Steve Wilson of Fine Agrochemicals was concerned that the ruling opened the door for less scrupulous manufacturers. "It casts a shadow over adjuvants which do have benefits and are useful to UK growers."

But Mr Newman believed the Pesticides Safety Directorates approach was sensible. "In the EU we are the only country that requires residue data for the use of adjuvants. If we had to do the work for every combination there wouldnt be an adjuvant industry."

Leaf wettability is key to retention

KNOWING whether a plants leaves are wettable or water repellent can help predict whether an adjuvant may help retain spray, according to Mr Webb.

Field beans, sugar beet, blackgrass, ryegrass and cleavers all have readily wettable surfaces, he said. "Adjuvants do not really increase retention on wettable foliage." Indeed, using an organosilicone product on sugar beet can increase run off, he pointed out.

But retention on water repellent species like cereals, peas, oilseed rape, wild oats, fat hen and sterile brome can be improved eightfold by using a suitable additive.

However, retention and coverage are only part of the picture. Uptake within plants, measured by radioactive carbon, may often be the key to pesticide performance, explained Dr Holloway.

Acetone ruled out

ONE outstanding adjuvant emerged at the meeting, though it is unlikely to reach the market. Researchers comparing products effects on spray retention and coverage found a standard acetone/water mix offered excellent results. But flammability rules out commercial use, said Mr Webb. &#42