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Disease risk for potato growers from alternaria and late blight this season

Following the second wettest winter on record across Britain, dealing with crop trash and volunteers has been difficult to tackle in the field.  This will lead to an increased inoculum reservoir and a heightened risk for development of alternaria and late blight this season. Technical Manager at UPL UK & IE, and potato crop specialist, Don Pendergrast discusses further.

“Late blight is usually foremost in a grower’s mind when developing potato fungicide programmes, but alternaria, also known as early blight, should be considered first.  Alternaria is a primarily a soil-borne fungal pathogen of potatoes, which infects crops early in the season. If left unchecked, the disease can cause defoliation and yield reductions of up to 30%. 

There are a number of fungicide actives that offer a cross-over control for both diseases.

Mancozeb is a multi-site contact fungicide which should form a key component of any potato fungicide programme as it offers protection against alternaria and late blight. Mancozeb, contained in products like MANZATE 75WG® is applied at full rate prior to the disease infection taking place, and has shown to be effective in a programmed approach for both diseases.  

Euroblight ratings on alternaria control show a 7-day interval of application for mancozeb to be a very effective control option, which can be further enhanced by partnering with other actives such as dimethomorph.    

Dimethomorph, contained in DIMIX®, applied early in the season, is a useful option in combination with mancozeb. Thanks to the translaminar locally systemic nature of dimethomorph, it protects new growth that occurs between each spray application, with the active moving up through the canopy.

The additional systemic activity of propamocarb contained as a formulation with dimethomorph in DIPROSPERO®, means there is a full complimentary package of modes of action when combined with mancozeb.  Dimethomorph in combination with mancozeb has proven to be a premium performer when protecting against early infestations of late blight.

Propamocarb and cymoxanil found in UPL’s PROXANIL® used at 1.5l/ha and combined with a multi-site contact such as mancozeb is ideal for resistance management and provides very good control.  Early infections of blight strains such as 37_A2 will require the most robust combinations to maintain control.  

Trials in 2019 showed that in this scenario the eradicant activity of propamocarb in PROXANIL in combination with mancozeb is the most cost effective and powerful solution.

UPL launched its free Blight Forecast App last year. Tools like this will be as important as ever given the complexities and pressures of controlling Late Blight in potatoes, particularly in this high-pressure season. Downloading the App gives growers both Hutton Period and Smith Period data, alongside additional layers of information such as leaf wetness and spray conditions on a field-level.

It will important that growers use every tool available, both in terms of technology, chemistry and IPM strategies to ensure the disease pressure legacy of this winter is managed successfully.”

Source: UPL UK & IE

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Lukie Pieterse, Editor and Publisher

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