Southern blight

About

Southern blight is a hot-weather soil fungus that rots plants at the soil line and attacks hundreds of crops, including tomatoes, peppers, beans, melons and sweet potatoes. Plants usually wilt suddenly and die.

Also called Southern blight, southern blight

How to recognize it

Symptoms

A brown to black rot forms on the stem at the soil line and can girdle it, so the plant wilts suddenly and permanently. A white, fan-like mat of fungus grows over the stem base and soil, dotted with round tan to reddish-brown sclerotia the size of mustard seeds. Fruit touching the soil can get sunken yellow spots that collapse.

Often confused with

White mold also makes white growth, but it prefers cool weather and forms larger, irregular black sclerotia.

Worse when

Hot, humid weather (77 to 95°F), moist but airy soil, and acidic soil.

How it spreads

Sclerotia survive for years in the top 2 to 3 inches of soil and in plant debris and move with soil and plant material.

When

Hot, humid summer weather.

What to do, gentlest first

Prevention works best; most sprays only protect healthy leaves and can't cure infected ones. Always read and follow the product label.

1. Rotate with grasses Prevent

   Rotate with corn, wheat or other grass crops, and Clemson advises not planting tomatoes after beans, peppers or eggplant.

2. Bury debris and adjust soil Prevent

   Turn infected debris deeply under to bury sclerotia, and raise acidic soil pH, since the fungus is held back above pH 7. Clemson suggests calcium nitrate at transplanting for tomatoes.

   Have your soil tested before liming.

3. Resistant rootstocks Prevent

   NC State lists tomato rootstocks with resistance for grafting.

4. Remove plants and nearby soil By hand

   Remove infected plants along with the soil and sclerotia around the stem base, bag them, and clean up debris after harvest.

5. Few home options Conventional spray

   Fungicides NC State lists are for commercial growers; home gardeners should rely on rotation and sanitation.

   Follow the label, including which crops it may be used on and how many days to wait before harvest.

Plants it affects

Cantaloupe (muskmelon), Carrot, Eggplant, Gladiolus, Green beans (snap beans), Pepper (sweet and chili), Pineapple sage, Potato, Southern peas, Sweet potato, Tomato, Watermelon