Watch out for a possible leap in cereal diseases after the combination of warm conditions in early May following the high April rainfall, growers are being urged.
High grain prices mean there’s now much more at stake if barley doesn’t receive adequate disease protection between T2 and harvest, says Iain Hamilton of Syngenta. Depending on location, this can be anything up to six to eight weeks
Rain-splash conditions last month will have helped the establishment of wet weather diseases such as Septoria tritici in wheat, and Rhynchosporium and net blotch in barley, warns Syngenta technical manager Iain Hamilton.
Now, hotter conditions will have compounded this by shortening the development period for Septoria, he says, while also encouraging temperature-loving diseases, such as rust.
“As a result of these factors, it will be vital for growers to consider all these possible disease threats when making their fungicide spray decisions in May,” says Mr Hamilton, “whether they are spraying at T2 in winter wheat and winter barley, or T1 or T2 in spring barley.
“This is especially the case since recent growing conditions have led to the sort of lush crop growth that rust thrives on. Septoria is in virtually all wheat crops now, while brown and yellow rust are being found in susceptible varieties,” he adds.
Overall, Mr Hamilton says the weather conditions have increased the need to consider a three pronged-approach with T2 fungicide decisions in wheat and barley - using a strobilurin for green leaf retention and persistent protection, especially against rust; a triazole for curative disease control; and Bravo for added protection against Septoria tritici in wheat and activity against ‘leaf spotting’ in barley. As well as being a major problem in Scotland, he says leaf spotting is increasingly being reported further south.
“As the basis for a three-pronged strategy, consider using Amistar Opti as a cost-effective way to get hold of the components of the strobilurin Amistar plus Bravo,” Mr Hamilton says, “then add the triazole in. Alternatively, if growers have already chosen a strobilurin plus triazole, then strongly consider adding Bravo to create the three-pronged strategy,” he adds.
Looking at T2 in wheat in more detail, Mr Hamilton says effective protection is so important because the flag leaf which it is designed to protect can contribute around 40% to yield.
Also, although rust control can be achieved with an effective triazole, the addition of a rust-active strobilurin extends the length of protection - to as much as six weeks - and acts at different stages of the rust life cycle, to enhance triazole activity, he adds.
Similarly in barley, high grain prices mean there’s now much more at stake if barley doesn’t receive adequate disease protection between T2 and harvest, he says. Depending on location, this can be up to six to eight weeks.
For maximum green leaf protection during grain-filling, he says T2 barley mixtures should therefore include a strobilurin for persistence - with independent trial plots having shown that including Amistar Opti not only improved green leaf area 41 days after spraying, but also reduced spotting 32 days after spraying and boosted yield. As an alternative to mixing Amistar Opti with a triazole, in situations where there is less need for curative disease control it could be mixed with the fungicide Kayak, he suggests.
Meanwhile for spring barley at T1, Mr Hamilton says because of Rhynchosporium sensitivity shifts to triazoles, Kayak makes a good choice. As well as boosting barley yield, it provides a different mode of action against the tough diseases of Rhynchosporium and net blotch to triazoles, while its broad-spectrum activity also extends to eyespot and mildew, he adds.
“With the importance of protecting spring barley early - while also managing triazole sensitivity shifts - Kayak at T1 makes an ideal tank mix partner choice. It can be mixed with Amistar Opti for extra protection against Rhynchosporium or net blotch, or with a suitable triazole for extra curative action against Rhynchosporium or net blotch,” he adds.
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