Black Dot (disease)

Black Dot disease is caused by the plant pathogen known as Colletotrichum coccodes (C. coccodes).  It is able to effect all of the underground parts of the potato, including the roots, tuber, and stolon. C. coccodes is also able to infect the stem and foliage of the potato plant[1]. It can be introduced into an area by planting an infected tuber, and then spreading to other plants. A sign of Black dot disease is black microschlerotia that are produced by the pathogen, and can be found on the roots, the tuber, the stems, and the leaves[2]. This can be used to diagnose Black Dot. Symptoms of Black Dot disease include silvery lesions on the surface of the tuber, brown or black lesions on the leaves, leaf wilting, and chlorosis[1].


Black Dot disease can be seen in many of the places that grow potatoes around the world. In a lab cultured sample taken from Black Dot of potatoes, conidia grew best at 82.4 F and a pH of 6[1]. High humidity and temperature are conducive to the inoculation of Black Dot[3]. The disease is spread more quickly when there are a bunch of schlerotia in the soil, rather than when the foliage is inoculated by conidiospores[2]. Infection often occurs in early spring, but it takes until later in the growing season for symptoms to appear[4]. Plants that are stressed are more susceptible to getting Black Dot than plants that are more healthy[5].


Spraying fungicides early on in the growing season, before the inoculation of Black Dot, can reduce the severity of the infection. If fungicide is applied later in the growing season, it has little to no effect on the disease. For fungicides to have a lasting effect, they must be sprayed multiple times[4]. Cultural control is another way to manage Black dot disease. This includes using crop rotations that aren’t a host plant. The rotation needs to be fairly long (3-4 years), to allow for the survival structures to die[6]. Other methods include using disease free seeds, planting in soil with relatively low moisture levels, and by controlling the level of humidity and the temperature when the tubers are being stored[3].


  1. ^ a b c Lees, A. K.; Hilton, A. J. (2003-02-01). “Black dot (Colletotrichum coccodes): an increasingly important disease of potato”. Plant Pathology. 52 (1): 3–12. ISSN 1365-3059. doi:10.1046/j.1365-3059.2003.00793.x. 
  2. ^ a b Tsror (Lahkim), Leah; Erlich, Orly; Hazanovsky, Marina. “Effect of Colletotrichum coccodes on Potato Yield, Tuber Quality, and Stem Colonization During Spring and Autumn”. Plant Disease. 83 (6): 561–565. doi:10.1094/pdis.1999.83.6.561. 
  3. ^ a b “Idaho Potato Diseases – Black dot”. Retrieved 2017-10-23. 
  4. ^ a b Ingram, Jason; Cummings, Thomas F.; Johnson, Dennis A. (2011-07-01). “Response of Colletotrichum Coccodes to Selected Fungicides Using a Plant Inoculation Assay and Efficacy of Azoxystrobin Applied by Chemigation” (PDF). American Journal of Potato Research. 88 (4): 309–317. ISSN 1099-209X. doi:10.1007/s12230-011-9195-2 – via SpringerLink. 
  5. ^ Andrivon, D.; Lucas, J.-M.; Guérin, C.; Jouan, B. (1998-08-01). “Colonization of roots, stolons, tubers and stems of various potato (Solanum tuberosum) cultivars by the black-dot fungus Colletotrichum coccodes”. Plant Pathology. 47 (4): 440–445. ISSN 1365-3059. doi:10.1046/j.1365-3059.1998.00267.x. 
  6. ^ “Black Dot Disease of Potatoes fact sheet”. Retrieved 2017-10-23. 

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