Expert Opinion: Ascra’s Curative Activity a Major Benefit for Growers
ADAS principal research scientist and fungicide expert Jonathan Blake says many of the available SDHIazole options perform well at the T2 timing, but some clear differences in its ability to control Septoria have developed over recent seasons.
These differences can be attributed to the speed of uptake and persistence within the plant leaf, which are influenced by the active’s relative solubility in water and how readily they penetrate the leaf layer.
Mr Blake notes that SDHI isopyrazam – contained in Syngenta’s Keystone and Seguris – is not as curative due to slower uptake, but has good persistence, so works better in a protectant situation. At the other end of the scale, a Vertisan plus Ignite mixture works very fast, so has better curative activity, but doesn’t have the same persistence as the rest, so is not as strong as a protectant.
Similarly, BASF’s fluxapyroxad, particularly when applied in the form of metconazole co-formulation Librax, gets into the plant quickly and effectively and showed itself to be very curative in 2016 trials.
“Aviator has a bit of both [speed of uptake and persistence], but Ascra seems to be very strong at both ends of the spectrum, so is both highly curative and persistent,” says Mr Blake.
In ADAS fungicide trials, products are pulled apart for their speed of uptake and curative activity by testing them throughout the Septoria latent period, with treatments applied at one, five, nine and 13 days after infection.
Mr Blake says in recent trials, Ascra showed itself to be highly effective throughout the latent period, giving between 80 and 90% control across all the timings.
Looking at the figures in more detail, that 80-90% equated to about 5% better control than Adexar when applied at the 1.2 L/ha rate and about 10% higher at 1.5 L/ha.
“Ascra gives similar control when applied nine days after infection as it would if applied at the start – usually you would see products fade at that point.
“It is giving very good control of Septoria and the extra curative activity during the latent period is extremely valuable to growers.”
Mr Blake adds that Ascra also adds persistency over other SDHI products, enabling it to delay the progress of disease within the plant for longer. “So when applied at T2, you will get lower rates of infection,” he says.
Laboratory research by Bayer in Monheim has shown that with fluopyram coming from a different class of SDHI to its partner bixafen in Ascra they can control different insensitive Septoria isolates.
But Mr Blake points out resistance could develop just as readily to both, so the only sensible way of slowing resistance developing is to use balanced mixtures with a range of modes of action.
So, it is perhaps good news that the concerns about key resistance management tool chlorothalonil having a negative impact are not evident with Ascra.
“Ascra seems to work well with chlorothalonil, having a neutral effect in a curative situation and a positive one in a protectant situation, so it is definitely worth having in the tank,” says Mr Blake.
2016 AHDB FUNGICIDE PERFORMANCE TRIALS
Ascra delivers bigger yields and outperforms other SDHIs in both protectant and curative situations