Black dot is increasingly top of mind these days, regardless of where you are growing potatoes. Symptoms can develop on almost all parts of the plant, including stems, leaves, stolons, and tubers.

Black dot leads to reduced yield and quality, fewer tubers, and reduced tuber weight. Foliar symptoms are associated with potato early dying and early vine decline.

What we know

Black dot is caused by Colletotrichum coccodes. With a wide host range and the ability to survive on crop residue and in soil, this soilborne fungal pathogen is endemic in many soils in Canada.

Black dot symptoms can be easily confused with early blight and brown spot on leaves, Verticillium wilt on stems, and silver scurf on tubers – a good reminder to seek an expert opinion or laboratory diagnosis to confirm which diseases you are facing.

Colletotrichum coccodes can be tricky – infections happen early in the season, with symptoms developing later.


¹ Syngenta Photo shows black dot sclerotina on potato stem
² Photo source

​​​​​​​Potato plants growing in sandy soils which are prone to sandblasting, or those in areas that see stress from high temperatures, poor drainage, or low nitrogen tend to have more severe symptoms. 

What you can do

1. Apply fungicides like Quadris Top^® preventatively, before row closure and targeting stems.
2. Manage crop stress as much as possible.
3. To limit tuber infection, avoid injury during harvest and harvest when skin is set.
4. Explore options to limit early season sandblasting.

 

What does Quadris Top do?

Quadris Top® contains two active ingredients, azoxystrobin (Group 11) and difenoconazole (Group 3). Applications of azoxystrobin before row closure help reduce black dot stem severity, while difenoconazole provides early season protection against early blight and brown spot.


Source: External replicated trials conducted in WA, 2004-2006, n = 3 (Cummings et al. (2008) Am. J. Pot Res DOI 10.1007/s12230-008-9040-4). One application of azoxystrobin applied as Amistar (112 g AZT/Ha) in 2004-2005 or Quadris (173 g AZT/Ha) in 2006 was made just prior to row closure.

Performance evaluations are based on internal trials, field observations and/or public information. Data from multiple locations and years should be consulted whenever possible. Individual results may vary depending on local growing, soil and weather conditions.

Always read and follow label directions. Quadris Top^® and the Syngenta logo are trademarks of a Syngenta Group Company.