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'Consequences of Alternaria still too much underestimated'
"The damage of Alternaria in potatoes is – certainly in recent years – greater than that of Phytophthora. Most growers have a strong focus on Phytophthora. But the consequences of Alternaria are still underestimated." That's what Jan-Willem Scherpenisse, arable advisor at Van Iperen, says.
According to him, early control – preferably before flowering – is essential to keep the disease under control. This year, for the first time, this is possible with the drug Propulse.
"Alternaria starts with some small spots in the leaf. That always seems a bit harmless, especially when you compare it with the large Phytophthora spots. But in the end Alternaria can swirl through the crop at least as quickly and devastatingly as Phytophthora. Then you can Phytophthora can still intervene after an infection. With Alternaria it is already too late and you can only watch the crop continue to die. This not only gives production a serious blow, but MH spraying can also be much less effective because this requires a healthy and vital crop. All in all, the consequences of Alternaria are often greater than you initially expected."
Jan-Willem Scherpenisse explains in a few sentences why Alternaria is such a vicious disease in practice. As far as he is concerned, the disease should be taken a little more seriously. "Growers still too often think that damage from those spots will not be that bad, until they see their crops deteriorate further later in the season. In that regard, Alternaria really is a silent killer."
Mancozeb and Difenoconazole
Ten years ago, Alternaria was still a disease that really only caused problems in southern parts of Europe. In the Netherlands, the damage was mostly limited, especially because many mancozeb-like products and strobilurins were used against Phytophthora at the time. At the same time, Alternaria was also kept sufficiently under control with these means. "But about five years ago we suddenly had to deal with greater damage, especially in the very sensitive variety Bintje. Research showed that a strain of Alternaria Solani had become less sensitive to substances from the group of strobilurins and that in a certain strain of alternaria alternata even complete resistance was found. Deploying these resources around flowering – which was common at the time – therefore no longer made sense. Fortunately, with products based on difenoconazole (including Narita®), we once again got our hands on a good weapon to combat Alternaria. Together with mancozeb – which has been used more widely in recent years to add manganese to the crop – we have been able to keep Alternaria reasonably under control," the advisor looks back.
'Propulse comes at the right time'
Now that mancozeb will disappear from the scene next season and the enforceability of the substance difenoconazole is also increasingly becoming a 'discussion point', Alternaria threatens to become a problem again. Moreover, the climate in the Netherlands also seems to be becoming somewhat 'southern', which means that the disease can thrive in any case.
Scherpenisse is therefore pleased that the drug has recently been Propel is allowed against Alternaria in potatoes. "Propulse comes at exactly the right time in that regard. Because with the disappearance of mancozeb, the rinse becomes very thin," he says.
This season, the advisor wants to introduce Propulse to the growers as widely as possible. He also recommends applying the product about 8 weeks after emergence, just before flowering, and then alternating it with Narita®. "Propulse is sprayed preventively, so well before Alternaria is visible. That may feel a bit 'premature' for growers, but it is essential to keep the disease out of the crop. It is also important not to extend the interval. to grow, i.e. no more than 14 days. And also important: keep spraying long enough, especially if the crop has to remain green well into September."
Botrytis and Sclerotinia
Scherpenisse advises growers to 'test' this year with Propel† "Because from next season, the product will irrevocably play an important role in potato cultivation." Finally, the advisor also points out the side effect of Propulse on Botrytis and Sclerotinia. "In this way, the product actually tackles all important fungi – except Phytophthora – and the crop remains greener and more vital."
