Tag Archives: late blight

Late blight alert – July 27th, 2017

This information is updated from an earlier article by Janice LeBoeuf.

We have had multiple reports of late blight in conventionally managed tomato fields this week.  Typically, this disease is well managed in tomatoes with a broadspectrum fungicide program including chlorothalonil.  However, high disease pressure due to environmental conditions, combined with a dense leaf canopy and rapid growth may have resulted in poor spray coverage and reduced efficacy.

Commercial growers should scout often and ensure they are using fungicides with good late blight activity in their fungicide program.  When late blight is in the area, spray intervals should be shortened.

Under continued high disease pressure, growers should consider adding a targeted late blight fungicide to the spray program.  If late blight has been identified in a field, use a fungicide with curative and antisporulent activity, see the table below for late blight fungicides and their properties. Continue reading Late blight alert – July 27th, 2017

Late blight alert – June 28

Late blight foliar lesionLate blight has been confirmed on tomatoes in Chatham-Kent.

Recent weather has been conducive to the development and spread of late blight.  Commercial growers should scout often and ensure they are using fungicides with good late blight activity in their fungicide program.  When late blight is in the area, spray intervals should be shortened. Continue reading Late blight alert – June 28

Late blight spores detected in Dufferin and Simcoe counties – 2

Advanced late blight symptoms

The Ontario Potato Board reports that for the second time this season, late blight spores have been detected in their spore traps in the Shelburne and Alliston areas. Late blight symptoms have not been detected, but it means that spores were present in the area. Continue reading Late blight spores detected in Dufferin and Simcoe counties – 2

Late blight update – July 28

Early foliar symptoms of late blightTo date, I know of no confirmed cases of late blight in Ontario, but there have been a couple of reports out of Michigan (on potatoes). Nevertheless, our experience of recent years would indicate we are likely to see it in Ontario tomatoes at some point in the season.

Remember that conventional tomato growers using a recommended fungicide program for early blight, septoria leaf spot, and anthracnose, are also protecting the crop from late blight infection. Cloudy and high humidity or wet conditions are favourable for late blight.  The pathogen prefers cool temperatures.  The disease is suppressed by hot, dry weather, but it can continue developing and spreading when suitable conditions return.

If late blight is found in the area, tomato growers should: Continue reading Late blight update – July 28

Late blight spores detected in Dufferin and Simcoe counties

Advanced late blight symptoms

The Ontario Potato Board reports that late blight spores were detected in their two spore traps in the Shelburne and Alliston areas on July 7. Late blight symptoms have not been detected, but it means that spores were present in the area. Continue reading Late blight spores detected in Dufferin and Simcoe counties

Late blight update – July 10

Early foliar symptoms of late blightTo date, I know of no confirmed cases of late blight in Ontario, but it has been found on potato in Branch County, Michigan (south of Battle Creek). Nevertheless, our experience of recent years would indicate we are likely to see it in Ontario tomatoes at some point in the season.

Remember that conventional tomato growers using a recommended fungicide program for early blight, septoria leaf spot, and anthracnose, are also protecting the crop from late blight infection. Cloudy and high humidity or wet conditions are favourable for late blight.  The pathogen prefers cool temperatures.  The disease is suppressed by hot, dry weather, but it can continue developing and spreading when suitable conditions return.

If late blight is found in the area, tomato growers should: Continue reading Late blight update – July 10

Fungicide efficacy summary tables for management of diseases in field tomatoes

By Cheryl Trueman, Ridgetown Campus – University of Guelph

About these tables:

  • Efficacy Table - AnthracnoseThese tables were created using results from replicated processing tomato field trials at the Ridgetown Campus, University of Guelph. Please contact the author for more information on research methods and copies of full reports. The tables are for information only and do not guarantee successful results with the use of any product.
  • Always check the most recent version of the product label before applying any product.
  • Only products labelled for ‘control’ of the specific disease are included in each table except where noted.
  • Click on each table to see larger versions.

Continue reading Fungicide efficacy summary tables for management of diseases in field tomatoes

Tomato late blight update

Tomato late blight has now been confirmed in Niagara Region, Bruce County, Wellington County, Chatham-Kent, Essex, and Elgin Counties. Credible reports have been received from Norfolk County, as well. It is widespread across the Great Lakes region at this point.

OMAFRA has been collecting samples of tomato late blight for a research project by L. Kawchuk, Agriculture and Agri-Food Canada, Lethbridge, Alberta. He is able to isolate the pathogen (Phytophthora infestans) from the samples to look at their fungicide sensitivity and determine their genotype. Most of the samples in the Great Lakes region the last couple of years have been the genotype known as US-23. It becomes a concern when there is more than one genotype in an area and when new genotypes are found (the higher the number, the more recent the genotype has been identified). New genotypes, for example, could be more aggressive and better adapted to our growing conditions. Continue reading Tomato late blight update

Late blight update – August 11

Late blight has been confirmed in numerous tomato fields in Chatham-Kent in recent days. Disease pressure is very high and weather conditions are good for disease development and spread.

Growers in the Chatham-Kent region or near other late blight outbreaks should consider shortening their fungicide schedule to five days while weather conditions remain favourable for late blight (moisture from rain, fog, dew and moderate temperatures). In areas of high disease pressure, such as Chatham-Kent, targetted late blight fungicides that have some level of systemic activity, should be added to the program. It is critical to rotate chemical families when using these products. Continue reading Late blight update – August 11