With minds on T2s, most crops look reasonably clean and strong but a disease explosion is only a rain shower away, warn experts
Consecutive weeks of mild and dry spring weather have eased the disease pressure facing crops, which could leave some growers pondering how to approach their T2s. However, the variable nature of some crops and often regional nature of disease pressure means there’s no ‘one-fits-all’ answer, explains ADAS’ Jonathan Blake.
Having viewed the variety plots at Bayer’s Crop Doctor site at Walpole St Peter, west of King’s Lynn, Jonathan says it’s difficult to share a general message. “Some days favour brown rust sporulation, others yellow rust, while it’d be unwise to not consider septoria at T2, even in crops which appear clean.
“Yellow rust appears more prevalent here than septoria at the moment, but septoria has a long latent period of around 21 days. So while many crops appear clean, they’re still to see the effects of the rain which fell the week before Easter,” he adds.
Looking through the varieties, it’s possible to find examples of all the main foliar diseases – septoria, leaf blotch, yellow rust and brown rust – just not all in the same variety, says Jonathan. With this in mind, he comments regarding T2s.
“In most cases, it’s likely to be a protectant rather than a curative situation which simplifies decision making. Any of the main foliar threats could quickly take hold if conditions favour, so the starting point is to base treatments around active substances with good activity on septoria.
“This could be SDHIs, azoles or QiIs, such as isoflucypram, mefentrifluconazole, pydiflumetofen or fenpicoxamid,” he suggests.
To understand the protectant performance of fungicides, Jonathan highlights the value of AHDB’s fungicide performance curves. “The AHDB performance data gives a clear representation of a fungicide’s activity against each of the main foliar threats,” he says.
“Some of these may be broader than others in terms of their spectrum, which may simplify T2 applications by reducing the need to add other chemistry.”
This article was taken from the latest issue of CPM. For more articles like this, subscribe here.
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