The impact of stretched fungicide spray timings is an area agronomy and advisory company Agrii researchers have been investigating in recent years
The impact of stretched fungicide spray timings is an area agronomy and advisory company Agrii researchers have been investigating in recent years alongside the value of both T0 and T3 sprays.In the absence of a T0 and with identical chemistry, theyve found that bringing the T1 forward from the ideal timing by five days and delaying the T2 by 10 days as can easily happen where the weather limits spray days hits yields by around 0.4t/ha. Their work, however, has also shown a T0 can completely reverse this loss. With larger acreages and increasingly variable weather, one of the most valuable roles of a T0 is the effective protection it gives against T1 and T2 timing problems, points out Agrii head of agronomy, Colin Lloyd (left). Having said that, analysis of 10 years of all our trials work to 2011 shows an average T0 yield response of just under 0.4t/ha. Whats more, the least T0 response weve ever recorded in a season has been 0.2t/ha. At a cost of around 12/ha, this is less than half the return it gives from wheat at 150/t. Our work also shows a typical response of just under 0.5t/ha from a T3 spray, he adds. Again, though, this varies widely between varieties from 0.2 to almost 0.8t/ha. Once more it underlines the importance of both variety choice and variety-specific agronomy in foliar disease management. As far as fungicide selection is concerned, Agrii research further demonstrates the importance of matching chemistry to both variety and season for the greatest value. Across five varieties over three years in six locations, the average response from a three treatment programme involving an SDHI rather than a standard triazole/strobilurin combination was just over 0.5t/ha. The extra yield benefit of the SDHI, however, ranged from less than 0.1t/ha with the least responsive variety to a full 1t/ha with the most responsive. And in wet seasons the average five variety response was over 0.9t/ha against just 0.2t/ha in dry seasons. Given the particular activity of SDHIs against septoria, Colin finds it no surprise they deliver more in wet years. Nor that his work shows a clear relationship between SDHI response and varietal resistance to septoria tritici. He stresses, though, that this understanding can make all the difference in deciding when and where to target the chemistry for maximum financial benefit. Equally valuable in this respect, he has no doubt, is the intelligence in-depth Agrii trials are providing every year on specific responses to a range of dose rates, using stacked triazoles to combat changing septoria sensitivity, and interactions between fungicides and protein quality as well as yield. We mustnt forget the importance of the right spraying technique either, he says. Our studies with different nozzles, forward speeds and water volumes at T2 highlight the considerable effect these specifics can have on spray coverage and disease development in the lower canopy, in particular. They show correct application is especially important with higher risk varieties, in high disease pressure seasons and where timings get stretched for one reason or other. More haste and less speed is, for instance, clearly the best approach to manage a variety like Oakley which already has disease in the lower canopy. So, here Id be sticking with a flat fan nozzle delivering 200 litres/ha at 610kph to ensure sufficiently good penetration. Only with more resistant varieties and lower disease pressures would I be switching to nozzles that allow faster work rates and lower water volumes.