The best margins over fungicide costs are achieved where barley fungicides are applied at the most effective and responsive timings, and tailored to the disease risks. Unlike wheat, where yield is limited by the amount of sunshine that can converted to carbohydrate and moved in to the ears, barley yield is limited by the number of grain sites set early the season before stem extension. In winter barley crops with more overwintering disease than the spring crop this is therefore a really key timing to protect the crop from disease and retain side tillers that might otherwise be lost to disease and so hang on to those grain sites. The later fungicide sprays timing at booting to early ear starting to emerge are aiming to retain green leaf area and fill these grains, aiding quality as well as yield.
While there is a relatively high risk of overwintering disease in winter barley crops and the T1 spray tends to be very responsive, in the spring barley crop early disease risk is often low. Omitting a spray though at T1 could run the risk of disease infecting the crop before it reaches the protection of T2 sprays, but on the other hand crops are often growing extremely rapidly and look very clean as they come up to stem extension. Recent work at SRUC has focused on trying to understand the risks better and work out in what situations sprays can safely be reduced or omitted. In 19 trials over three seasons the average yield response to a T1 spray is a little over 0.2 tonnes per hectare. The response to a T2 spray in spring barley in the same trial series was just over half a tonne but there was no additional advantage on average to using both a T1 and a T2 as the response to a two spray programme was also just over the same half tonne mark.
The trial series ran over 2017, 2018 and 2019 and it was only in the wetter May and June yards that any rhynchosporium appeared in trials and significant levels only developed on very susceptible varieties like Concerto. In 2020 it is likely that a good proportion of the crop will be fairly late drilled by which time soils will be warming and growth will be rapid. There is therefore scope this year to think about disease risk and, if the crop is clean and has a reasonable rhynchosporium rating like Fairing or Laureate, and heavy rain is not forecast then reducing or dropping the T1 fungicide could save money without putting the crop at undue risk. Of course, this is always situation specific and if there are diseases other than rhynchosporium which often occur on the farm, or there is not the resource to walk crops and check that they are clean some level of protection might be required.
The later sprays in winter barley this year may fall after the 20th May cut off for use of chlorothalonil, and in the spring crop this will almost certainly be the case. The risk of ramularia losses are therefore greater this season. There is some retained efficacy in prothioconazole, and the new Revysol azole also has efficacy although neither matches the efficacy of chlorothaonil. The efficacy of the multisite fungicide folpet is variable – although there are certainly situations where it might be helpful it does not offer the same level or consistency of protection as chlorothalonil. Ramularia is a stress triggered disease so take care with complex spray mixes and growth regulators to avoid any unnecessary stresses to the crop, which chlorothalonil may previously have masked. Similarly, there is more interest in crop nutrition to keep the crop green and in fungicides which can help with green leaf retention.
Article first published in the Scottish Farmer
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