Although the number of new finds of late blight in Manitoba seemed to have slowed down last week, new late blight finds were reported on potato from the Carman and Winkler areas this week, and on tomato crops east of Portage and east of Highway #75.
According to Dr. Vikram Bisht, plant pathologist, potato and horticultural crops with Manitoba Agriculture, all of the isolates tested so far are determined to be US23. “There is increasing metalaxyl insensitivity in the Pi from these samples and the use of Ridomil would probably have only marginal benefit.”
It is important to continue 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 seven days at various weather stations suggest mostly moderate risk in most of Manitoba. 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, Bisht notes a post-harvest treatment with phosphorus acid/phosphite fungicide could be considered for such fields.