Phytophthora blight on tomato

 

Phytophthora on tomatoes refers to diseases caused by oomycetes, also known as water molds, particularly Phytophthora infestans which causes late blight, and Phytophthora capsici which can cause buckeye rot and foliar blight. These diseases manifest as lesions on leaves, stems, and fruit, often leading to rotting and eventual plant death. Management strategies include using resistant varieties, improving air circulation, avoiding overhead watering, and applying fungicides.

Key points about Phytophthora on tomatoes:

 

    Late blight (Phytophthora infestans):

    This is the most common and destructive form of Phytophthora on tomatoes. It's characterized by dark, water-soaked lesions on leaves and stems, which can quickly spread and cause the plant to collapse. Infected fruits develop greasy, brown spots and can rot.

 

Buckeye rot (Phytophthora capsici):

This disease typically affects fruit in contact with the soil, causing tan or brown spots with concentric rings.

Other Phytophthora species:

Phytophthora capsici can also cause foliar blight with greasy, purple-brown stem lesions and leaf spots.

Favorable conditions:

Phytophthora thrives in cool, moist environments, particularly during periods of rain and high humidity.

Management:

 

    Resistant varieties: Planting tomato varieties with resistance to late blight can significantly reduce disease incidence.

 

Cultural practices: Improving air circulation by spacing plants adequately, avoiding overhead watering, and removing infected plant debris can help limit disease spread.

Fungicides: Applying preventative and effective fungicides, especially during periods of high risk, can help protect plants.

Crop rotation: Rotating crops with non-host plants can help reduce pathogen buildup in the soil.

Sanitation: Removing and destroying infected plant material can help prevent further spread.

 

Specific symptoms to look for:

 

    Leaves:

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Water-soaked or brown lesions, sometimes with white mold (sporangia) under humid conditions.

Stems:

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Brown lesions, often greasy or water-soaked, and can lead to stem collapse.

Fruit:

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Brown or black spots, sometimes with concentric rings (buckeye rot), or greasy, brown, sunken lesions (late blight).

 

Important note: While unblemished fruit from infected plants is generally safe to eat, it's best to avoid holding it for extended periods or canning/freezing it, as this can promote microorganism growth.