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.

Time to Monitor and Control Tomato Diseases

After several weeks of drought conditions moisture finally arrived at the end of June. This was a great relief for vegetable farmers as crops were showing signs of moisture stress.

Septoria Leaf Spot, Early and Late Blight are generally the most severe tomato diseases in Nova Scotia. Early blight-resistant tomato varieties aren't available, so gardeners have to use a combination of disease management practices.

Septoria leaf spot can occur at any stage of plant development. Symptoms may appear on young greenhouse seedlings ready for transplanting or be first observed on the lower, older leaves and stems when fruits are setting.

Early blight shows up as a leaf blight on the lower part of plants. The disease moves upward. As the disease progresses, leaves turn yellow, wither, and drop from plants.

Late blight may or may not arrive to Nova Scotia. In some years it can be devastating for tomato crop while in other years it is not present.

A management program for this disease is based on crop rotation, removal and destruction of crop debris from previous crops, staking, mulching, and timely application of fungicides.

Staking and mulching are important for leaf diseases, since staking keeps foliage and fruit from contacting the soil surface, and mulching cuts down on "soil splash" onto lower parts of the plant.  Soil particles often contain the early blight fungus spores, and mulching is a good way of keeping the fungus from invading plants.

A prevention fungicide program is very important. For detailed information on fungicides registered for field tomato please visit:

http://agrapoint.ca/Pest%20Management%20Guides/Vegetables/2012/Tomato%202012.pdf