By George Brown, Colorado State University Cooperative Extension, Horticulture
Early blight is a fungal disease that appears during the hot summer months.
Tomato leaves that have spots that begin as small, dark brown to black areas, and are turning yellow on the lower part of ;the plant, may indicate the presence of early blight. Spots frequently begin on the older, lower leaves inside the canopy of the plant where humidity is higher. As the spot develops, a concentric ring pattern can frequently be detected. This is the most diagnostic symptom of the disease and is the source of the name, "target spot," that is frequently found in popular garden books. As the disease progresses, leaves yellow, then drop. In severe cases, all the foliage can be blighted and premature leaf drop result. This in turn results in leaving the fruit exposed and sunscald results. Sunscalded spots are hard and tasteless and have to be cut out before eating the fruit.
Several cultural practices that will help to reduce tomato damage in the home garden are:
In some instances, there may be a need for spraying a fungicide. Only use a fungicide if you have an accurate diagnosis and know for sure what disease is attacking the tomatoes.
If the infestation is heavy, sulfur may be used to protect new leaves from becoming infected. Follow label directions, since the use of sulfur on hot days can burn plant tissue.
Other effective and commonly available fungicides for the home gardener are copper based. When selecting a suitable copper based fungicide read the label carefully to insure that it can be used, and follow the directions on the label.
Photos: Judy Sedbrook
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010