Grain prices would have to fall to below £27.50/t before fungicide use became uneconomic, according to a detailed investigation of responses to fungicide treatment in the HGCA Recommended List trials.

The analysis, carried out by variety expert Richard Fenwick for BASF, attempted to pinpoint where fungicide responses are economic and which agronomic factors had the biggest impact on the return on investment from fungicides.

According to Mr Fenwick the average yield response in Recommended List trials to the HGCA’s fungicide programme over the past six seasons ranged from 1.29t/ha to 3.56t/ha.

But in each season fungicide use was economic when margins over fungicide cost were calculated using an average farmer programme cost of £55/ha.

“In fact, grain prices would have to drop to £27.50/t before they became uneconomic.

It shows grain prices shouldn’t really affect fungicide programmes.”

That calculation was based on farm fungicide programmes achieving the same yield response as the HGCA “blockbuster” programme designed to keep all disease out, he admits.

“But NIAB trials comparing full, half and quarter doses across Recommended List trials suggested a half-rate programme, which is equivalent to what farmers would typically spend, typically yielded 95% of the full programme.

“In practice it would make very little difference to whether it was economic to spray fungicides.”

Not surprisingly perhaps, he found variation in conditions from year to year, and moisture availability were the biggest factors affecting how much return growers get from fungicides.

“Unfortunately, growers have very little control over either of these.”

But other factors, such as variety, previous cropping and soil type, do influence the response to fungicides to a greater or lesser extent, and could be manipulated to target fungicide use more effectively, he believes.

“I’m sure a lot of growers use broadly similar programmes across the whole farm.

These days it is all about attention to detail.”

Growers should concentrate spending on fungicides on crops in situations where the best responses are likely, such as first wheats on moisture-retentive soils, he says.

“Conversely, there is no point throwing lots of money at a crop on a drought-prone soil if the potential isn’t there – they are the sites where you can cut back on fungicides.”

Susceptible varieties gave the best returns on fungicide use.

“That means they should be targeted, possibly even for increased doses.

Growers certainly must not think because a variety gives a massive response to a fungicide they can cut down on dose as they have got a big leeway – you could start losing that response,” he concludes.

mike.abram@rbi.co.uk

more detailed analysis of the report’s findings will appear in Crops on 11 March.