The Trouble with Tomatoes

How to prevent an infestation of blight on the tomato plants in your garden.

If you are an avid vegetable gardener or are just getting your knees dirty for the first time, you will most likely plant some tomatoes. They are a great tasting summer fruit and are easily grown across most parts of Canada. Unfortunately, they are not problem-free. One of the biggest challenges tomato gardeners can face each year is early or late blight. Preventing an infestation of early blight is the best way to keep the plants healthy and ensure you get a great harvest throughout the season.

Early blight is caused by a fungus in the soil. It starts when wet weather occurs after planting and the fungus moves from the soil to the leaves and up through the plant. It is made even worse when weather becomes hot and humid.

When infected, the bottom leaves typically turn yellow, wither and drop from the plants. The fruit becomes undersized and the plants produce low yields. The effects of early blight are evident in August and can occur almost overnight. Late blight generally appears just as quickly in September. Once tomato plants are infected with blight, there’s nothing you can do to treat them: that’s why prevention is so important.

The best way to control early or late blight is to practice crop rotation within the garden, staking the plants to keep them off the ground and mulching heavily with 20-30cm of straw. The latter will help to insulate the plants from the fungus during watering and helps conserve soil moisture. Also, space the plants at least 30 inches apart when planting to allow for good airflow within the rows.

Using a low-toxicity fungicide, such as Green Earth’s Bordo Copper Spray, is also quite effective at controlling this fungus if applied as a preventative treatment. The best time to spray is when plants are 12-18cm high and every 7-10 days after that depending on the weather. Make sure to follow the directions on the container and spray more frequently and in the morning if the weather is hot and humid. Copper spray also helps to control other plant problems such as mold and leaf spot.

Do not let early blight prevent you from planting tomatoes. With a little work, you can have a great crop!

Green gardener Mark Cullen is a radio and TV personality, author of 18 gardening books and answers thousands of questions at