Stress factors, such as low rainfall so far this season and reduced crop nutrition, could increase the risk of Alternaria (early blight) in potato crops according to Syngenta Technical Manager Andy Cunningham.
“Any agronomic factor that increases stress on the crop can act as a precursor for Alternaria infection, as well as the severity of the outbreak,” he said. “Early season infection and subsequent loss of leaf area inevitably has a greater impact on yield.”
Because of the increased risk, Andy believes growers should consider Alternaria protection earlier in their blight programme, as fungicide control of the pathogen must be applied preventatively.
“Alternaria treatments have historically been focussed to start around the end of June or beginning of July,” he explained. “Where growers have identified an increased risk of stress, or have historically suffered from Alternaria losses, however, that may need to be brought forward this season.”
To counter the Alternaria threat, Mr Cunningham suggested the use of Amphore Plus (which incorporates the strong late blight protection of mandipropamid with the Alternaria activity of difenoconazole) through the primary risk period: “Using the pre-formulated combination delivers 20% more difenoconazole with each application to boost alternaria protection, compared to the maximum permissible rate of the active when applied as a straight product,” he added.
Andy also highlighted that the cumulative effects of multiple stresses can have greater effects on potatoes, even at relatively low levels. “Plants that are already performing sub-optimally under stress from moisture or nutrient deficits, for example, can then be impacted badly by further pressures.
“That has been especially evident with the increasing impact of heat stress on potatoes. Enabling plants to be better prepared to cope with the adverse effects of heat stress with applications of the biostimulant, Quantis, could help mitigate the effects of other stress factors and reduce the crops’ susceptibility to Alternaria.”