Growers should be on the lookout for late blight
US (MI): Tomato diseases are on the rise
Early blight infects foliage and ripening fruit and seems to be especially troublesome for growers who have not kept up on their preventive fungicide sprays. Infection can occur at the point of attachment to the stem and through growth cracks and wounds on the fruit. The early blight fungus causes dark brown, leathery sunken spots with concentric rings. Infection is greatest in warm weather (75 to 85 degrees Fahrenheit). Heavy dews, extremely humid weather and abundant rainfall are essential for early blight. A 3 to 4 year crop rotation can help reduce the levels of the early blight fungus in the soil.
Septoria blight is severe in our tomato research plots in East Lansing and appears to progressing rapidly on plants that were not protected with fungicide. This is a common foliar disease and may occur on the tomato plant along with other tomato-loving pathogens. Rapid defoliation of Septoria-infected plants may occur when the weather is warm with frequent rain showers. This loss of foliage results in yield loss and sunscald of the remaining fruit. In general, a tomato plant infected with Septoria will have lower leaves that have become peppered with small, dark circular spots. These spots will increase in size, with the centers of these spots becoming light tan in color with dark margins. The disease normally spreads from the lower leaves to the upper leaves on the diseased plants.
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