Symptoms of Sclerotinia Blight may appear anytime from mid- to late- season when weather conditions are cool to moderately warm and wet. The first symptom of Sclerotinia blight is the wilting and yellowing of lateral or main branches. Affected branches near the soil line must be closely examined for definitive identification of Sclerotinia. A fluffy or cottony, white moldy growth (mycelium) develops around diseased areas of lower stems. The mycelium of Sclerotinia is most easily observed in mornings when dew is present or after a rain, and may disappear later in the day when sunlight dries the lower canopy. This is in contrast with the coarse, rope-like mycelium of southern blight. Dead areas (lesions) develop on affected stems that appear sunken, elongated, and light tan to almost pale white. Soon entire limbs wilt and turn yellow. Affected branches die and turn dark brown in color and eventually whole plants may be killed. The small seed-like survival structures (sclerotia) of Sclerotinia are black and irregularly shaped and range in size from 1/24 to 1/16 inch. These sclerotia may aggregate into larger masses that appear similar to mouse droppings. Sclerotia may not be evident during the early stages of disease development. Sclerotia are formed in and on infected stems, leaflets, pegs, pods, and roots. A characteristic symptom of Sclerotinia blight is stem shredding. Diseased stem tissue will shred easily when rooled between the thumb and fingers. Shredding is the result of the rotting of all stem tissues except the vascular strands. Shredding of pegs results in loss of pods in the soil harvest.
Because Sclerotinia blight can be very damaging and difficult to control, steps should be taken to limit the spread of the fungus and its entry into clean fields. Tractors, plows, combines, and other farm implements leaving infested fields should be carefully cleaned and washed prior to entering clean fields. Soil and peanut straw should be completely removed from these implements. Cattle fed with peanut straw from fields infested with Sclerotinia should not be pastured on clean fields. Peanut hay taken from infested fields should not be fed to cattle grazing on clean fields. To eliminate the potential for importing the disease into fields on peanut seed, seed should be treated with a fungicide known to reduce Sclerotinia. A combination of cultural and chemical management practices will provide the most satisfactory control. Practices that reduce moisture retention in the canopy and promote aeration should be adopted. These include planting on a raised bed, and avoidance of narrow row spacings and overly heavy seeding rates. Irrigation timing is also important. Enough water should be applied at each irrigation to permit thorough and prolonged drying of the soil surface before the next application. Excessive vine damage should be avoided. A fungicide program is usually required where Sclerotinia is a problem. Proper timing and use of an appropriate method of application are essential for maximum disease control. Fungicides should be applied in a preventative manner to achieve thorough coverage of basal stems. Fungicides only protect healthy plant parts from infection. They do not cure established infections or kill sclerotia. Please contact your local county extension office for current information.