Teagasc has confirmed that the loss of fluazinam as an end-of-season blight control spray will have a major impact on the Irish potato industry.
“Its value lay in the fact that both foliage and tubers were effectively protected from blight attack,” Dr. Stephen Kildea said.
This was the case until 2019 when it was first reported that the efficacy of fluazinam had reduced considerably. Causing the problem has been the development of a new blight strain – 37A2.
“The challenge now is that of finding a replacement for fluazinam.
“There are alternative, end-of-season products available, including one brought to market this year by BASF.
“And, obviously, growers must make best use of these options. But there is a limitation on the number of times these products can be used.”
Potato production
This year has seen an increase in the area dedicated to potatoes that are suited to chipping and crisp production. But there are some indications of these varieties being susceptible to early blight, caused by the fungus Alternaria solani.
“It depends on the variety and the season. Processing varieties do have a susceptibility to alternaria, or early blight,” Kildea said. “And it does need to be controlled.
“Alternaria and phytophthora infestans are different species of pathogen; alternaria is a true fungus, phytophthora is not. As a consequence the chemistries that are available do not cross from different species.
“So, it’s a case of using a true fungicide when it comes to controlling alternaria.”
Blight
Early blight takes the form of dark brown spots with circular rings giving a target appearance. These spots may merge to form dead patches.
The disease can be differentiated from late blight as white mould-bearing spores do not develop around the foliage spots during humid weather conditions.
In Europe, a heavy increase of early blight infestation occurs from mid-July onwards, especially during hot and dry weather or when the potato crop is under stress, and on physiologically older plants.
The disease then starts spreading from the lower leaves to the middle and finally upper leaf levels.
According to Kildea, the only product available at present that is effective against both pathogens is fluazinam.
“But this is no longer an option, given the resistance-related issues now associated with that specific chemical,” he said.
“When it comes to getting specific control over alternaria, a number of SDHIs are available. A number of azoles are also registered for use with potatoes in this context.”