In mid-August of 2014 Late Blight (Phytophthora infestans) was observed in commercial and backyard potato and tomato crops across central Saskatchewan. Subsequent development and spread of the disease was limited in potato crops but severely damaged the foliage and fruit of tomato crops. Tests conducted by Agriculture and Agri-Food Canada Lethbridge confirmed that the strain of Late Blight that occurred in Saskatchewan (and much of North America) in 2014 was more damaging to tomatoes than to potatoes or other Solanaceous crops.
Late Blight carries over from season to season on infected seed potatoes. As much of the seed potato crop grown in Saskatchewan in 2014 would have been exposed to Late Blight and could be carrying the pathogen there is an increased risk of Late Blight reoccurring in 2015. Commercial and hobby growers are urged to pay special attention to the health of the seed potatoes they decide to plant. Seed tubers showing signs of Late Blight (see the picture below) should not be planted. Growers should be aware that some cultivars of potato (Norland, Shepody, Pontiac, Russet Norkotah and Yukon Gold) are much more susceptible to infection by Late Blight than others (Russet Burbank, Alpine, Classic and Milva). The tomato cultivar Defiant (Johnny’s Seeds) has been bred with enhanced resistance to Late Blight – and trials conducted by the University of Saskatchewan indicate that Defiant produces good yields of small but high quality fruit.
Potato growers should begin scouting for signs of blight soon after emergence of the crop. Commercial growers should be ready to apply blight control products as early and as often as required. There are a few fungicides available to backyard gardeners that will provide some degree of protection against blight. Growers need to be aware that these products must be applied before the Blight arrives – they will not stop a Blight outbreak once it becomes established. As blight thrives under cool moist conditions, growers are urged to avoid wetting the foliage if possible and to time irrigation events so that the canopy has time to dry before nightfall. Staking tomatoes increases air flow the canopy and this slows establishment and spread of Late Blight. Having a good hill over the developing potatoes protects the tubers from infection by any blight spores that wash off infested foliage.
For more information of Late Blight and tips for managing this disease see the Late Blight Fact sheet at: www.usask.ca/agriculture/plantsci/vegetable/factsheets.htm
If you suspect late blight or any other problems in your crop contact Gardenline (306 966-5865), Doug Waterer at the University of Saskatchewan (306 966-5860) or Connie Achtymichuk with Saskatchewan Agriculture at (306 787-2755) immediately.
Late Blight on potato leaves, a potato tuber and on tomato fruit.
Potato tuber picture c/o I. Evan (Alberta Agriculture)