Remedy for Black Fungus in Withering Tomato Plants

Fusarium Wilt

• You may not know your tomato plants have Fusarium wilt until they reach the flowering stage, when symptoms are often more pronounced. The disease, involving the fungus Fusarium oxysporum, causes the vascular system of tomato plants to turn brown or black as the tissues clog with fungus. Failure of the vascular system leaves the plant's foliage without water and nutrition, which leads to wilt.

  Select tomato varieties labeled with an "F" in conjunction with the variety name. This means the plants are resistant to the fungus; they may still become infected, but shouldn't be seriously compromised. There are no chemical controls for treatment. You should rotate tomato crops out of the growing space, using the same space no more frequently than every four years.

Fusarium Crown Rot

• Fusarium crown rot is caused by the same fungus that leads to Fusarium wilt, Fusarium oxysporum. A hallmark of this infection is blackened leaves that also wilt. Plants may wilt during the heat of the day and recover overnight. The disease gradually weakens plants and may kill them. The fungus lives in the soil and enters the plant through its root system or wounds in the tissue, spreading through the interior of the plant. Warm temperatures aid the fungus to develop and spread.

  You can reduce the incidence of disease by practicing good crop rotation, only planting tomatoes in the same spot every four years or more. Water your crops with well water where possible, avoid the use of ammoniacal nitrogen, maintain a soil pH of 6 to 7, and practice crop rotation with a crop such as corn or lettuce rather than legumes, suggests the University of Florida IFAS Extension. Plant resistant varieties to avoid infection, as the spores remain in the soil and can spread through the air.

Early Blight

• Early blight is caused by the fungus Alternaria solani. The disease affects plants' lower leaves first, and causes yellowing of leaves. Black circular spots form on leaves, sunken black lesions on fruits and black cankers on stems of infected plants. Typically a late-season disease, rain and warm temperatures influence the its spread.

  Good sanitation in the garden helps prevent early blight, as it survives on garden debris and plant material. Plant resistant varieties and improve air circulation between plants to prevent development of blight. Remove garden weeds, collect all ripe fruit when picking, and rotate tomato, eggplant and potato crops out of the area for three years to prevent the spread of infection. The Clemson Cooperative Extension suggests treating severe infections with maneb, mancozeb, chlorothalonil or fixed copper.

Late Blight

• The fungus Phytophthora infestans causes late blight. This blight develops under moist conditions, during periods of cool nights and warm days. The disease proceeds quickly, producing black spots on plant leaves. The spots start at the edges of foliage, have uneven borders and a water-soaked appearance. You may also see lesions on the stems, water-soaked spots on fruit and fruits that turn brown.

  You may spread the infection from plant to plant by touch or through working in the area. The University of New Hampshire Cooperative Extension recommends against using fungicides to treat infected plants, as they will not cure the infection. Plants that have the disease must be removed from the garden and disposed of. They should not be placed in compost piles.