How to Identify and Cure Late Blight of Tomato (Phytophthora infestans)

Are your tomato plants suddenly dying? Have the tomato leaves turned brown? Have the stems collapsed? Are the tomato fruits leathery and brown? If so, your plants may have been infected with this disease: late blight of tomato - caused by the pathogen Phytophthora infestans.

Phytophthora infestans is an oomycete, which is a water-loving, fungus-like organism. This particular pathogen infects many solanaceous plants, which means it causes disease of plants in the nightshade family, such as potatoes, tomatoes and aubergine - known in American english as eggplants.

The disease caused by Phytophthora infestans has a tragic, world-changing history. Phytophthora infestans is notorious for contributing to the devastating Irish potato famine of the 1840s.

In this video I focus on tomato plants. I will show you the interaction between Phytophthora infestans and tomato plants, causing the disease we know as tomato late blight. Late blight on your tomato plants can quickly kill your tomato plants in as little as two weeks.

The disease means the tomato leaves develop brown or black lesions and wilt, rot or collapse. Tomato fruit infected by Phytophthora infestans turn a leathery orange-green colour, eventually turning brown and rotting.

I’m first going to help you spot the symptoms and learn how to diagnose tomato late blight. I’ll then give you six natural, organic steps you can take to prevent tomato late blight ruining your tomato harvest in future years.

If you want to learn more about this fascinating pathogen and the way it spreads, I’ve added some links to relevant scientific papers below.

Credits to Unsplash and Wikimedia Commons for providing several static images.

🔬 Scientific papers about Phytophthora infestans:

Production, survival and infectivity of oospores of Phytophthora infestans
https://bsppjournals.onlinelibrary.wi...

Survival of Phytophthora infestans sporangia when exposed to solar radiation
https://apsjournals.apsnet.org/doi/ep...

Survival of Phytophthora infestans in surface water
https://apsjournals.apsnet.org/doi/ep...


⌚ Timestamps:

00:00 How to translate Phytophthora infestans
00:25 The tragic history of late blight
00:41 Is Phytophthora infestans a disease?
01:45 How Phytophthora infestans spreads
02:26 How to spot leaf symptoms of tomato late blight
04:06 How to spot symptoms on tomato fruit
05:12 Can you eat fruit from infected plants?
06:05 Step 1: Keep tomato leaves dry
06:44 Step 2: Improve airflow around your tomato plants
07:26 Step 3: How to dispose of blight-infected plants
08:15 Step 4: Can you re-use tomato potting mix?
08:50 Step 5: Why you should clean your gardening tools
09:09 Step 6: Growing blight resistant tomatoes