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Manitoba potato disease report for August

August 15, 2016 - New late blight finds were reported on potato from Carman, Winkler areas and on tomato crops east of East of Portage and east of Highway #75, according to Vikram Bisht. Frequent fungicide applications are being applied to control the disease; and in one case the tomato plants have been pulled out and destroyed.

Samples have been collected for strain identification. All of the previous samples, tested by Lethbridge Research and Development Center were determined to be US-23 strain.

"There is increasing metalaxyl insensitivity in the Pi from these samples and the use of Ridomil would probably have only marginal benefit," says Bisht.

It is important, he continues, to scout for late blight, especially in low lying, irrigation pivot center, wheel tracks of irrigation systems (guns/pivots), tree-line protected areas and under hydro-power lines (areas where applicators may have difficulty covering).

It is also critical at this time to monitor potato and tomato plants in home gardens. The DSVs (late blight risk values) accumulated over 7-days at various weather stations suggest mostly moderate risk in most of the province. There is forecast for rain and risk of thunderstorms today afternoon in many potato growing areas. Full fungicide coverage of foliage in high risk areas should be maintained.

Due to continued high moisture levels in many fields, it may be helpful to harvest the low lying areas last, so it will be easier to manage the storages.

Also, a post-harvest treatment with phosphorus acid / phosphite fungicide could be considered for such fields, adds Bisht.

August 17, 2016  By MAFRD