NIAB - National Institute of Agricultural Botany

Orson's Oracle

What should be on the label?

Posted on 03/02/2012 by Jim Orson

I said a few weeks ago that I would return to the 1970 edition of the Approved Products for Farmers and Growers. In those days approval meant that the product efficacy had been assessed and ‘it did what was said on the tin’. Efficacy assessment was not part of the registration process, but it was de rigueur to enter products into the voluntary Approvals Scheme.

Personally, I’ve regularly questioned why products have to be assessed for efficacy. It’s understandable that there are obligations on the label regarding crop safety and safety to following crops. The argument for statutory efficacy testing is that pesticides should not be used in the environment unless they do a useful job. On the other hand, the market would soon drop the products that didn’t do the job. That takes place despite a statutory efficacy assessment.

On the other hand, a target needn’t necessarily be on the label for a product to be widely adopted to control it. Trifluralin had a huge market for black-grass control in cereals, but the weed was not listed on the label as being susceptible.

In addition, the label recommended dose to do a particular job is often ignored. The best example of this is with cereal fungicides. In efficacy testing for authorisation the product is only applied once and no other fungicides are used. In practice, a programme of different fungicide products may be used to control the target. In this situation, adopting a lower than recommended doses is inevitable.

The other issue with the recommended dose is that it’s set to control the most difficult target on the label. Significantly lower doses may suffice for many of the more susceptible targets listed. Everyone can quote examples where this takes place. It’s regrettable that much of the dose information generated during initial development trials isn’t detailed on the label.

The other efficacy issue that now has great emphasis during the authorisation of products is resistance management. Overall I welcome this, but there are issues relating to some of the restrictions imposed. All too often it is closing the stable door after the horse has bolted. A good example of this is resistance to the ‘fops’ and ‘dims’. To be fair, the labels suggest that a wider view is taken of resistance management than just the specific measures they outline.

In many cases resistance is inevitable unless rather extreme measures are taken. Bayer imposed the need to use mixtures with Atlantis. However, it soon became clear that the only way to prevent resistance to Atlantis, and products that share its mode of action, was not to use them on a regular basis. Mixtures may have delayed the inevitable, but not by much.

I am increasingly convinced that resistance management is more of a socio-economic issue rather than merely producing guidelines and introducing some restrictions of use on labels. Resistance to outstanding pesticide-based solutions can occur very quickly. Glyphosate weed resistance developing in crops genetically modified to be tolerant to this herbicide. Roundup Ready was initially a great option, not only because of the level of weed control achieved but also the ease of management. The cost of the GM seed also meant that the breeders invested more in developing varieties. This resulted in farmers totally relying upon this one herbicide solution year after year. Weed resistance has taken a little of the icing off the cake but the area of Roundup Ready crops has not diminished.

There really is a need to learn the lessons of the past. This would suggest that an even more restrictive use may increase the lifelong benefits of new modes of action known to be vulnerable to resistance development. After the experience of the strobilurins, is it wise to allow two SDHI-based fungicides per crop?

Unfortunately, new discoveries are very active substances with doses, at most, of a few hundred grams/ha required to achieve control. This typically results in them having a single site of action making them more vulnerable to resistance development. The low doses and single site of action is a reflection of rapid screening methods in the discovery phase. They also mean that products based upon such active substances are more likely to be cheap to produce and, perhaps more importantly, they are more likely to get through our rigorous registration systems.

I’m rather surprised about the direction this blog has taken. I started by indicating I was going to discuss the contents of the 1970 Approvals book. That’ll have to wait for next week.

 

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