Potatoes in Canada

Features Agronomy Diseases
Manitoba potato report: Aug. 9

Disease update
The number of new finds of late blight seems to have slowed down, even though the disease continues to be a concern. All of the isolates tested so far, were determined to be US23. Late blight was found in market-garden plots of potato and tomato in Oakville area, in Central Manitoba. 

There were scattered rains and strong winds on Aug. 4 and 7, which may have spread the disease. 

It is extremely 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). Full fungicide coverage of foliage in high risk areas should be maintained. 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 the province. There is forecast for a few rain days in many potato growing areas, in the coming week. 

Due to wet and warm conditions there are reports of stem rot/blackleg. Hail damage and European Corn Borer (ECB) injury appears to have contributed to some of the stem rotting. Early blight in general appears to be very minor.

Pest update
The aphid counts remained low in the third week (July 5-11) and the fourth week (July 12-18) especially in the southern seed production area. Potato aphids, but not Green Peach aphids (GPAs), were found in these weeks. There were no aster leafhoppers (ALH) and potato leafhoppers (PLH) noted in the traps. 

In the fifth week (July 19-25), the aphid counts have increased significantly over the previous week. Green peach aphids were trapped from the Portage area only. The potato aphids were trapped in all the three seed production areas. Potato aphids are fairly efficient PVY transmitters, but not as efficient as GPAs. The “other aphids” in the traps are poor transmitters, but make up with higher numbers. 

With other crops in the region maturing and near harvest, the aphids will find the green potato crop very attractive. It may be helpful to the seed growers to consider tank mixing insecticide with the aphid-oils application, especially if the crop planted had some level of PVY in the seed itself. 

The results from suction and pan traps in seed fields for the third, fourth and fifth week can be found here.

Currently, there is no report of any serious Colorado potato beetle (CPB) feeding in commercial potatoes. 

European Corn Borer:
Delta trap monitoring for the ECB moths using pheromone lures continue to show some adult moth activity – in Carberry, Brookdale in Rural Municipality of North Cypress-Langford, Treherne (RM of Victoria), Shilo (RM Cornwallis), Glenboro (RM of Glenboro-South Cypress) and Carman (RM of Dufferin) area. 

After a peak activity in mid-July, the number of trapping has reduced. After the appearance of very young larvae (Figure 1) was the trigger for insecticide application in fields close to last year’s serious infestations. Some ECB injury and larvae were noticed in the Carberry area. 

Insecticide application could be considered when significant larval counts appear, and especially in areas where the stem infestation was high in 2015. Please consult the 2016 Manitoba Guide to Field Crop Protection for the choice of insecticides.

 


August 11, 2016
By MBPotatoes.ca

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