Topical tips for better disease control

A few simple steps to improve fungicide application can deliver big benefits in terms of disease control, especially when spray timings are stretched or spraying conditions are less then ideal.

With disease pressure building, the rewards are likely to be substantial this season. Better fungicide efficacy boosts yield and improves return on investment, important when grain prices are under pressure, says Agrovista technical manager Mark Hemmant.

In addition, keeping ahead of disease ensures fungicides act mainly as protectants, reducing the chances of diseases such as Septoria developing resistance to key chemistry, he adds.

“Sprays are rarely applied in ideal conditions, especially on farms with large areas to cover. Over the past eight years, we’ve carried out a lot of trials examining how to improve fungicide efficacy when application has been compromised in some way,” he explains.

“They show that paying attention to a few key application areas such as boom height, adjuvant use, nozzle type and water volume can make all the difference when it comes to how well disease is controlled.”

Nothing, however, can fully make up for poor timing, he stresses. “Letting a key timing slip can have a big impact on yield. Our trials show even a week’s delay at the flag leaf timing can cause yield potential to fall away dramatically, by around 0.5-1t/ha, and by much more as the delay increases (see table).”

Nozzle type

Standard 110-degree flat fan nozzles remain the best option when applying fungicides to wheat, delivering a good droplet spectrum that ensures effective coverage and good penetration at the usual 100-200 litres/ha rates, says Mr Hemmant.

“Flat fans were consistently more effective when used with triazole/SDHI treatments in normal spraying conditions, producing an average yield increase of 0.29t/ha over air induction (AI) nozzles in five years of trials.

“However, the larger air-filled droplets produced by air induction nozzles are less prone to drift, which is useful in marginal conditions. This gives operators a much better chance of maintaining correct fungicide timings.”

Adding Velocity, an oil-based adjuvant, can help lift efficacy of AI nozzles, improving droplet structure to aid penetration and spread on the leaf, says Mr Hemmant.

“It’s beneficial with any nozzle, but particularly with AI nozzles. It can improve performance to levels near those achieved by flat fan nozzles, allowing growers to get job done without having to sacrifice efficacy and yield from using a 'poorer' AI nozzle.”

Alternating forward-facing (30-degree) and vertical nozzles improved flat fan and AI performance, aiding coverage and penetration. It also reduces drift, probably because it allows air to pass through the spray curtain, reducing the tendency to create eddies behind it, he explains. 

Boom height

When it comes to application technique, boom height has a major effect, says Mr Hemmant. “Apart from bad timing, this is probably the biggest cause of poor fungicide performance. The optimum boom height is 0.5m above the crop. Doubling it typically increases drift by a factor of 10 with flat fan nozzles.”

Water volume

Water volumes of 100 litres/ha delivered better disease control than 200 litres/ha in Agrovista trials targeting yellow rust, says Mr Hemmant. “Even under high disease pressure we saw yields rise by up to 0.5t/ha. This is partly due to the finer spray improving coverage and the fact that each droplet contains more active ingredient.”

Halving the water volume also means less downtime travelling and filling the sprayer, which can increase work rates by a third, he explains. “That means more of the crop can be treated at the optimum timing.”

He warns against reducing volumes further, even if it is permitted on the product label. Drift can increase if smaller nozzle apertures are required, and smaller droplets can also dry too fast in hot conditions, reducing uptake. Crop penetration may also suffer.

“However, on rare occasions with very high Septoria pressure, higher (200 litres//ha) water volumes have performed better than lower (100 litres/ha) volumes.  Adding Velocity also allows growers to maintain product performance in these situations,” says Mr Hemmant.

Table 1: Effect of timing – SDHI timing v triazole (yield t/ha)

Treatment (litres/ha)

23 May

(ideal T2 timing)

30 May

(week too late)

12 June

(very late)

Librax (1.0) + Ennobe (0.5)




Librax (1.0)




Adexar (1.0)




Aviator (1.0)




Seguris (1.0)




Ennobe (1.5) + CTL (1.0)










24 March 2015

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