{"id":13047,"date":"2014-11-14T00:00:00","date_gmt":"2014-11-13T11:00:00","guid":{"rendered":"https:\/\/www.farmersweekly.co.nz\/cereal-killer-on-the-rampage\/"},"modified":"2014-11-14T00:00:00","modified_gmt":"2014-11-13T11:00:00","slug":"cereal-killer-on-the-rampage","status":"publish","type":"post","link":"https:\/\/www.farmersweekly.co.nz\/news\/cereal-killer-on-the-rampage\/","title":{"rendered":"Cereal killer on the rampage"},"content":{"rendered":"Reading Time: <\/span> 2<\/span> minutes<\/span><\/span>

Triazole fungicides are less effective\u00a0against this disease than they were seven\u00a0years ago.<\/p>\n

At the same time Septoria became\u00a0resistant to existing fungicides, a\u00a0new mode of action arrived on the\u00a0market in the form of SDHI (succinate\u00a0dehydrogenase inhibitor) fungicides.\u00a0These have prevented significant\u00a0production losses because of the presence\u00a0of the disease both in New Zealand and\u00a0Europe.<\/p>\n

However, Poole cautioned against\u00a0over-using SDHIs in order to maintain\u00a0sensitivity to the chemical. He said they\u00a0should not be used more than twice in\u00a0one cereal crop. Neither should they be\u00a0used curatively.<\/p>\n

Septoria, which is a stubble-borne\u00a0disease, has the potential to reduce\u00a0harvest yields by as much as 50%.\u00a0The spores are dispersed by both wind\u00a0and rain-splash and require 48 hours of\u00a098% humidity in order to infect the crop.<\/p>\n

Poole said the jury was still out on\u00a0whether irrigation had the same effect of\u00a0rain in so far as creating the conditions\u00a0that facilitate the spread of Septoria.<\/p>\n

The disease has a long latent period \u2013\u00a0time between the spores landing in the\u00a0crop and symptoms appearing \u2013 which\u00a0has been calculated at 250C thermal\u00a0time.<\/p>\n

A rough guide to calculating thermal\u00a0time is to add together the maximum\u00a0and minimum temperatures and divide\u00a0by two. With a maximum temperature\u00a0of 15C and minimum temperature of\u00a05C it would take 25 days to reach 250C\u00a0thermal time.<\/p>\n

Over the past two seasons damp\u00a0springs, susceptible cultivars, and\u00a0resistance to fungicides had meant\u00a0Septoria had been a big problem for\u00a0wheat growers.<\/p>\n

Poole said there was potential for\u00a0Septoria to be a problem again this\u00a0season because there was a lot of\u00a0innoculum in early sown crops. However,\u00a0the wet autumn meant that more crops\u00a0were sown later and this would reduce\u00a0the risk of the disease.<\/p>\n

How Septoria develops depends\u00a0entirely on the season.<\/p>\n

There were cultivars showing resistance\u00a0to Septoria and while late-sown wheat\u00a0crops are less susceptible to the disease,\u00a0there were yield penalties associated with\u00a0late-planted crops.<\/p>\n

Resistance to strobilurins, which have\u00a0been widely used since the 1990s, was\u00a0first reported in Europe in 1998 so the\u00a0chemistry only offered crops six years\u00a0of protection before resistance began to\u00a0occur.<\/p>\n

To date strobilurin resistance has been\u00a0recorded in 50 pathogens around the\u00a0world with the first reported cases in NZ\u00a0occurring in 2006.<\/p>\n

\n

Septoria tritici blotch has become the principle disease in wheat crops over the past two seasons.<\/p>\n<\/div>\n

Strobilurins are still effective against\u00a0rust but they were no longer effective\u00a0against Septoria.<\/p>\n

Triazoles have become gradually\u00a0less effective over the years with\u00a0laboratory tests showing Septoria\u00a0had become 10-100 times less\u00a0sensitive to triazoles since the early\u00a02000s. They needed to be used\u00a0at a high dose rate in order to be\u00a0effective.<\/p>\n

In the United Kingdom, the efficacy\u00a0of triazole fungicides against Septoria\u00a0had continued to decline and the\u00a0field performance at low doses has\u00a0deteriorated further.<\/p>\n

Rob Craigie from FAR explained\u00a0that resistance to triazoles was\u00a0complex and not all triazoles were\u00a0affected in the same way.<\/p>\n

He cautioned against over-using\u00a0triazoles and suggested using them\u00a0with a partner chemical which had a\u00a0different mode of action to reduce\u00a0the risk of resistance.<\/p>\n

This may improve disease control\u00a0while increasing efficacy.<\/p>\n

While SDHI\u2019s will control Septoria,\u00a0FAR\u2019s Nick Poole stressed the need\u00a0to use them judiciously because there\u00a0were not any new modes of action on\u00a0the horizon. Their efficacy needed to\u00a0be maintained.<\/p>\n

There is already some pathogen\u00a0resistance to SDHIs in Europe.\u00a0Poole said SDHIs should always\u00a0be used in combination with another\u00a0mode of action.<\/p>\n

\u201cThe new SDHI fungicides used\u00a0in combination with triazoles are\u00a0effective at controlling the disease\u00a0Septoria.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"Disease management in\u00a0wheat is undergoing a\u00a0significant change because the\u00a0fungicides that have been\u00a0relied on for decades are\u00a0becoming less effective.\nNick Poole from the Foundation for\u00a0Arable Research (FAR) says the strobilurin\u00a0fungicides farmers have been using are\u00a0no longer effective against Septoria tritici\u00a0blotch, which has been the principle\u00a0disease in wheat crops over the past two\u00a0seasons. While these fungicides will still\u00a0control rust, they won\u2019t work against\u00a0Septoria.\n","protected":false},"author":33,"featured_media":13048,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_FSMCFIC_featured_image_caption":"","_FSMCFIC_featured_image_nocaption":"","_FSMCFIC_featured_image_hide":"","footnotes":""},"categories":[3],"tags":[],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t