May 27, 2016
Iain Richards Blog: BYDV horrors underline intelligence-based agronomy need
The horrific extent of BYDV infections in many winter wheat crops has become all too apparent with surging May growth in temperatures of up to 27oC accompanied by more than enough rain.
Thanks to a November insecticide timed from Agrii weather station-based TSum predictions of aphid development we have managed to keep infections in high risk late September, Deter-treated crops to only small foci of infection. This won’t significantly affect yield. But it underlines the value of basing our agronomy on the most up-to-date local scientific intelligence rather than just what we see ourselves at the time.
In just the same way, I have no doubt that what we know from our decision-support service not what is currently evident on the leaf will prove every bit as vital in our Septoria management.
The cold spring and late start to treatments has allowed us to keep the upper leaves nice and clean, thanks to good spray timings. However, with plenty of disease in the base of our wheats and our weather stations recording persistent rain splash events and temperatures well into the ‘twenties, infections occurring now are predicted to be well into their latent periods in a matter of days.
This means we aren’t holding back on our T2s, currently going onto rapidly emerging flag leaves. We’re basing these on the SDHI we find gives the best all-round Septoria activity, fluxapyroxad with a combination of epoxiconazole and metconazole, keeping rates up and generally including a multi-site protectant.
It isn’t a cheap fix but, with typical T2 trial responses of 1.5t/ha under nowhere near the disease pressures we’re currently seeing and clear warnings from our Septoria prediction system, it’s essential. After all, once we have lesions on the leaf it’s too late to do anything about them.
I’m glad to say, the excellent job done by carefully-targeted strobilurins at T1, varieties with good resistance and a week of hot, dry weather have largely allayed our earlier concerns over yellow rust.
Light leaf spot in our winter OSR is nowhere near as concerning as it was, either. The cold April meant our mid-flowering sprays only went on right at the end of the month and we included a decent rate of prothioconazole alongside fluopyram. With flowering starting late and drawing to a timely close, a single sclerotinia spray has been all we’ve needed in almost every case.
The madness of early May growth in the warm and wet brought even our later-drilled spring barleys along nicely, with early PGRs proving very effective in encouraging tillering. All our crops are now getting a T1 of prothioconazole to deal with rynchosporium and net blotch plus a broad-leaved weed clean-up. The sheer speed of recent growth has meant more than a little crop – as well as agronomist – stress, so magnesium and manganese deficiencies have shown-up widely. With an even shorter growing season than normal, we certainly haven’t waited for T1 to go in with necessary foliar nutrient support.