Little and often…
Little and often…
To strob or not to strob? That is the question for weather-struck wheats which are looking the worse for wear, as Gilly Johnson finds out
KEEP that wallet in your pocket; think twice before splashing out on strobs this season, says Suffolk-based independent agronomist, Simon Draper. The extra cost may not be justified on many crops which could struggle to reach normal yield potential, he argues.
The strob yield boost shrinks with crops which are below par, he reckons. Hes put together a ready-reckoner (right) to pinpoint where strobs will be worth it – and where they wont.
"We know that strobs can give more yield, but the question is, how much? Were expecting relatively low yields from our later drilled wheats, from crops which have been sitting in waterlogged soils, and also prices are relatively low. Spending on strobs should be questioned."
It can be seen from Mr Drapers ready-reckoner, that these scenarios work against strob use. Only in high performance crops, where the strob yield boost is significant, is the investment likely to be worthwhile.
Instead he favours another route to higher yields: a little-and-often fungicide strategy.
He pioneered this system back in the days before strobs arrived, so it was based around triazoles. The little-and-often tactic wins out in two ways. It is cheap in terms of variable costs – the agchem bills can be halved compared to a conventional two/three-spray programme – and its also more effective, he says, because by delivering a pre-emptive strike against infection, plants never have to waste energy by mobilising their own defences.
Independent trials confirm a triazole-based little-and-often programme can work well, delivering yield increases of between 7-12%, he says. "Building in a strob to this approach would only deliver another 3% in extra yield potential, because we are starting from a higher baseline." So plumbing this into his ready-reckoner, the economics rule out including a strob within a little-and-often programme.
His basic system is based on Opus (epoxiconazole), with the first spray at 0.25 litres/ha, followed 10 days later by 0.2 litres/ha, then 0.25 litres/ha followed by another 0.2 litres/ha, with a final low dose of Folicur (tebuconazole) on the ear. A little Fortress (quinoxyfen) might be included to combat mildew early on, depending on varietal susceptibility, says Mr Draper.
Capacity
In total, wheat could be given five sprays, with the first treatment going on about mid-April. Over the whole season the crop might only be given the equivalent of one full dose of Opus – hence the savings.
The case against is that growers must be prepared to go into the crop perhaps every 7-10 days, a commitment which can add to fixed costs. The farm must have the spray capacity and the manpower to cope. "Its not for everyone, or for every field," says Mr Draper.
And its certainly not to the taste of agchem manufacturers. Not surprisingly, they take issue with Mr Drapers advice that lower yield potential crops should not be given strobs. Trials done by BASF, manufacturer of kresoxim-methyl based fungicides (Landmark etc) show that thin plant stands benefit from a greater relative yield boost from strobs due to an increase in green leaf area, particularly lower down the canopy (Crops, 20 January, p29).
ADAS plant pathologist Bill Clark reckons that cutting strobs from your fungicide programme will compromise yield and margins: "HGCA work on the physiology of strobs has shown their biggest effect, especially at T1, is keeping leaves 3 and 4 green for longer.
"Its these leaves which are important in thinner crops – so strobs are actually equally, or in some cases more, effective important in thin crops as they are in thicker crops. By cutting strob inputs in thin crops you end up with a self-fulfilling prophecy; the crop is going to be low yielding, so you cut inputs, the yield is reduced – and youve proved yourself right!"
The "little-and-often" approach has been criticised on the basis that iot breaches the strob resistance management guidelines, which limit strobs to two sprays.
"For economic reasons, Im not using strobs in my little-and-often programmes, so the resistance issue doesnt arise," says Mr Draper. "We are complying with the guidelines. But I would question the argument that it might encourage resistance, because we are keeping disease out right from the start, and maintaining a constant supply of triazole within the plant, so the pathogen is not given a chance to develop and become resistant."