Early Blight (Alternaria solani) of Potato

Primary damage to potatoes by early blight is attributed to premature defoliation of the potato plants, which results in tuber yield reduction.  Initial infection occurs on older leaves with concentric dark brown spots.  Disease severity is highest when potato plants are injured, under stress or lack proper nutrition.

Please consult the 2014 Potato Crop Weed and Pest Control Guide for information on control options.

Be on the Watch for Onion Diseases

Cool, wet weather this past week is conducive to disease development in onion fields. Monitoring is necessary for Alternaria sp., leaf blotch (Cladosporium sp.) and Stemphylium sp. on direct seeded onions as these diseases were found in onions grown from sets.

Please consult the Guide to Pest Management in Onion for more information on control options. 

To learn more about Stemphylium, a devasting onion disease, please see this informative article which has good pictures to help you identify the disease.

Watch for Tomato Diseases

Tomato Leaf Mold

 
Due to a wet growing season the tomato crop, especially in high tunnels, has been infected by leaf mold. Some growers experienced difficulties associated with leaf mold in June while others are getting their crop infected now.

Tomato leaf mold is caused by Fulvia fulva (also known as Cladosporium fulvum).  This fungus attacks during cloudy, humid weather and can be particularly severe in plastic greenhouses.  We certainly have had weather that would favour this pathogen.

 
Tomato leaf mold can spread very quickly under humid conditions such as we have been experiencing lately.  It is key (even more important than fungicides) to increase air flow through the crop and to lower the humidity.  It is advisable to crack the vents at dusk and increase night-time temperatures so that they are above outdoor temperatures to prevent high humidity in the greenhouse. 

Heat during rainy days might also be required.  Pruning off the lower leaves will help to get air flow through the crop and reduce infection.  Air movement with fans is also a good idea.  If the infection is serious and the crop is nearing the end of production, it might be best to harvest what you can without investing more money/effort in control. 

There are not many fungicide choices.  Fontelis and Pristine are registered for Cladosporium suppression on other crops, but both fungicides are also registered on tomato for Botrytis and Alternaria control.

Early blight, botrytis and septoria have all been found in tomato crops.  Given warm, humid weather it is likely that before too long we might see late blight on tomatoes.  In addition to proper canopy management, pruning out the diseased foliage and proper ventilation, it may be necessary to keep ahead of diseases by providing periodic fungicide applications.  For more information please see the Tomato Management Schedule - a guide to weed, insect and disease management in tomatoes.