June 9, 2014
Latest research highlights importance of Autumn decisions in what foliar disease control
Wheat variety and seed treatment choices at T(-1) can markedly improve the efficacy and flexibility of spring fungicide spraying, reveal the latest in the long-standing series of integrated disease management trials at Agrii’s Throws Farm Technology Centre. So much so that, trials manager, Steve Corbett is adamant that autumn decisions must be the first priority in foliar disease control wherever yellow rust is a risk.
“Across much of southern and eastern England, this year is the second bad rust season we’ve had in the past three,” he pointed out. “Rapid growth from early sowings and extremely mild conditions meant we saw significant levels of yellow rust in early-sown plots of key varieties before Christmas. A dry spring held infections at bay until Easter. But warm, wet conditions since then have seen the disease cycling rapidly, really putting the pressure on spraying at a time when reliable spray days have been hard to find.”
Although not drilled until October 26, this season’s wheat disease management trial at Throws has seen yellow rust develop strongly in susceptible varieties. At the most recent scoring in mid-May, for instance, Solstice and KWS Kielder receiving only a single purpose seed dressing (SPD) averaged 12.1% and 11.7 % leaf infection respectively. In complete contrast no yellow rust was recorded at all in Crusoe in the absence of foliar treatment.
A T0 on April 4 followed by a T1 on April 15 pegged back disease development well in the Solstice and KWS Kielder controls to average just 0.45% in mid-May. But when T1was the first foliar fungicide, leaf infection levels averaged nearly five times this level across the three different T1 regimes.
Compared to the SPD, Galmano Silver (two thirds rate fluquinconazole) seed treatment more than halved yellow rust infection in the two susceptible varieties without foliar treatment from an average of 11.9% to just 5.6%. It also almost halved average leaf infection levels post-T1 in the absence of a T0.
“These results underline the importance of either growing varieties with a high level of yellow rust resistance or ensuring the best, early season protection,” commented Steve Corbett. “They also reinforce the yield benefits of up to 0.75t/ha we saw from fluquinconazole across all foliar fungicide regimes in our 2011/12 trials.
“Our research consistently shows resistant varieties and the best seed treatment are both highly effective at keeping early yellow rust infections at bay for an extended period – far longer than we originally thought would be possible in the case of fluquinconazole. This means there’s no temptation to bring T0s forward to deal with early problems and stretch subsequent spray timings as a result. Which, in turn, leaves less opportunity for Septoria as well as both brown and yellow rusts to take hold.
“Wherever yellow rust is a threat, I’d strongly advise treating any variety with a resistance score of less than 5.0 with two thirds rate fluquinconazole at T(-1) as a matter of course,” he suggested. “And given the speed at which we’ve seen varieties break down in the recent past, I’d also be considering it wherever scores are less than 7.0; especially for September drillings.
“After all, we know just how difficult it can be to get well-timed T0s applied when we’re dealing with large acreages and heavy ground, in particular. What’s more, our trials show that stretching the T1 to T2 gap by a relatively modest 15 days can hit easily yields by 0.4 t/ha.
“In our experience, good variety and seed dressing choices at T(-1) can make all the difference, giving us the leeway for the less-than-ideal foliar fungicide timings we are so often forced to accept.
“As such, we should see them as the first – and arguably most important – of our annual wheat disease management decisions, based firmly on the same value per hectare considerations as our other fungicide inputs rather than merely cost per tonne of treated seed.”