November 23, 2017
Aphid Alert Tool Proves Invaluable in Early Winter BYDV Protection
A BYDV alert tool developed over the past four seasons by Agrii’s decision support team is proving invaluable in helping agronomists and their growers across the country maintain the most effective winter cereal aphid control in the face of increasingly variable national and local weather.
The tool – in the form of an app for agronomists’ smart phones, tablets or laptops – employs the company’s national network of physical and virtual weather stations to provide daily in-season tracking of local aphid risks using the established T-Sum method. It is also proving useful ahead of the season in assessing local risks for both treated and untreated seed at any sowing date based on the warmest and coolest seasons of the past 30 years.
“Our BYDV Alert App gives an immediate graphic representation of the accumulation of day degrees over 3oC for any site each day through the key aphid risk period for autumn-sown crops,” explained developer, Dr Francesca Salinari.
“We know it takes an average of 170 of such day degrees for the second generation of wingless aphids to be produced, leading to the rapid spread of BYDV. After a further 170 degrees the third generation will appear, at which stage their progression and BYDV spread becomes exponential.
“We also know the benchmark temperature requirements for wheat emergence and the length of effective protection given by both seed treatments and pyrethroid sprays.
“By bringing this intelligence together with automatically up-dated daily temperature records from our weather stations we can provide accurate estimates of aphid risk and spraying alerts for first and follow-up insecticide foliar applications at any site in the country.
“Our decision support app gives agronomists an up-to-date map of the UK colour-coded for aphid risk in 25km squares, together with the ability to assess the current risk for any of their crops by individual location and sowing or last spray date at the touch of a button,” she pointed out.
Agrii’s BYDV Alert App records for the past few years underline the extent to which aphid risk has varied with sowing date, seed treatment and season as well as location, making spraying decision-making increasingly difficult.
Last season, for instance, untreated crops sown at Salisbury in the last week of September reached the high risk start of the second aphid generation by mid- November while those receiving a seed treatment needed a foliar spray by late-December 22 (Figure 1a). In contrast, untreated crops sown on October 20 only became high risk from Christmas time and treated crops never reached an alert threshold by the end of the year (Figure 1b).
The exceptionally warm autumn and early winter of 2015, however, saw untreated late -September sown crops on the same site becoming high risk before the end of October and needing a second foliar application as early as the beginning of December. The high risk period for treated crops started almost a month early than 2016 and these too reached an alert for a second foliar application by the end of December (Figure 2a). What is more, even treated late-October sowings saw a significant aphid risk by Christmas that season (Figure 2b).
“With the latest information on aphid migration from Rothamsted, our agronomists and their growers have found this addition to our decision support service invaluable in planning and targeting their follow-up sprays at just the right time to catch new generations of aphids before they can really spread the virus,” reported Dr Salinari.
“Such timely treatment is, of course, also important in combatting the development of the pyrethroid resistance we know to be a growing problem in grain aphids,” she added. “It is particularly valuable given the growing frequency of milder autumns and early winters. And it is set to become even more critical if neonicotinoid seed treatments are restricted.”
T-Sum tracking of aphid development saved Andy Nash and his Wiltshire, Hampshire and north Somerset growers being as badly caught out by BYDV as many in 2015/16. So it isn’t surprising the Agrii BYDV Alert App has become an essential tool in their winter cereals management .
Andy has been using T-Sums – based on his own calculations from local weather data – for several years to achieve the greatest possible precision in his BYDV spraying recommendations.
So the App, and Dr Salinari’s weekly BYDV Bulletin which preceded it, fitted his requirements perfectly.
“Traditionally, people used to go in with their BYDV spray as soon as their untreated crops got to the 2-3 leaf stage then reckon the job was done,” he recalled. “This was perfectly OK when we could rely on a decent winter from mid-November to restrict aphid development.
“With the seasons as variable as they have become, though, this approach simply isn’t good enough any longer. On the one hand, it means large numbers of migrating aphids may arrive after the spray and escape. And, on the other, their progeny may go to spread BYDV widely before declining air temperatures bring their development to a halt. Which is exactly what happened for many in 2015/16 when aphids were still flying here in January.
“At the same time, relying on post-em herbicides for our grass weed control always used to give us the flexibility to add a pyrethroid at relatively little cost when going through the crop later on if we had any aphid concerns. Now, thanks to resistance, our grassweed control is largely pre- and peri-em. So in many cases an extra pyrethroid spray means the extra cost and time of a separate pass through the crop.
“With the Francesca’s App we can see exactly how aphids are developing in our crops – treated or untreated – from their actual sowing dates. Watching the graph building allows us to plan and time our spraying for the maximum effect and economy. We then reset the clock to track any development from later-arriving migrants in case we need to spray again.
“That way we only ever spray when and where we need to. If the season is particularly mild – as it was in 2015 – we use the two sprays really needed for most crops and even give our treated, late-sown wheats a December follow-up. And if it’s cooler, like last season, we only spray the majority once. This has to be the best approach environmentally as well as economically.”
Andy Nash and his growers also find the BYDV Alert App valuable ‘out-of-season’ in planning specific seed treatment and early crop protection programmes for the increasingly wide range of wheat sowing dates necessary in the face of black-grass pressures.
“It brings much needed science into the whole business of BYDV control in a practical and immediately understandable way,” he stressed.