AgronomyLate blight alert in southern Ontario

Late blight alert in southern Ontario

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A&L Biologicals Laboratory has confirmed the presence of late blight spores in the Alliston, Ont. area. Spores were not detected in the spore trap near Shelburne, Ont., but conditions for the development of late blight are perfect not only near Alliston but across the province of Ontario.

To date, there are no reports of potato late blight in Ontario. But potato fields must be protected against this devastating disease to avoid economic losses. In fields where there is water standing between the rows, aerial spraying may be an option.

Rainy weather with relatively cool nights favours potato growth, which means that new leaves may be unprotected two days after spraying.

Preventative fungicide sprays, regular field scouting, the destruction of volunteers and the elimination of cull piles are effective management practices that reduce the risk of late blight.

Preventative Fungicides

According to many growers, Bravo Zn plus an EBDC (Penncozeb, manzate, etc.) have proven to be effective in reducing the incidence of late blight incidence.

Late Blight Specific Fungicides

  • Curzate has a kickback effect of approximately 36 hours. In other words, it will kill the late blight lesions that have developed within the last 36 hours.
  • Revus: Very effective
  • Acrobat
  • Allegro
  • Forum
  • Gavel: good choice close to the end of the season
  • Orondis Ultra
  • Phosphorous acid-based products (foliar sprays may cause some phytotoxicity)
  • Presidio
  • Ranman and Torrent (same active ingredient)
  • Tattoo C
  • Copper hydroxide: kills late blight spores

Late blight specific fungicides should be used with Bravo Zn or with an EBDC to reduce the development of resistance.

Remember to hose down your sprayer after spraying an infected field. An ounce of prevention is worth a pound cure!

More information

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