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Early and Late Tomato Blights and Leaf Spot

Posted: September 3, 2015

While working the Wrightstown Grange Fair “Ask a Master Gardener” help desk I had many home gardeners either report that this was a bad season for “tomato blight” or ask questions about “blight” and how it can be avoided or “cured.”

There are many publications available on the Extension website which provide details for identification, explanations, and management tips but I felt a quick overview–comparative chart might be useful for many of us to use as a starting point. I hope it is helpful for the remainder of this season and for next year.

tomato blight chart

Disease Early Blight Late Blight Septoria Leaf Spot
Responsible Fungus Alternaria solani Phytophthora infestans Septoria lycopersici
Description of Foliar Damage One or two spots per leaf, approximately ¼ to ½ inch in diameter. Spots have tan centers with concentric rings in them and yellow halos around the edges. Spots start out pale green, usually near the edges of tips of foliage, and turn brown to purplish-black. In humid conditions, a fuzzy mold appears on the undersides of leaves. Numerous brown spots appear on the leaves, approximately 1/16 to 1/8 inch in diameter. The spots lack a yellow halo, and, upon close inspection, have black specks in the center.
Description of Fruit Damage Dark, sunken spots appear on the stem end of fruits. Brown, greasy, leathery spots appear on green fruit on the top and sides of the fruit. In humid conditions, white mold also forms. Fruit are not affected, though sun scald can be a problem due to foliage loss.
Description of Stem Damage Dark, sunken cankers at or above the soil line. Black and brown spots appear and spread. Entire vines can be killed very quickly in periods of high humidity. No stem damage.
Optimal Conditions High humidity, and temperatures between 75 and 85 degrees F and is spread by rain or watering events. High humidity, temperatures between 60 and 70 degrees F and is spread widely by wind and locally by rain or watering events. High humidity, temperatures between 68 and 77 degrees F and is spread by rain or watering events.
Organic Treatment Remove lower leaves after first fruit sets, remove affected leaves as they appear, plant tomatoes in a different area next year. Consider containers with fresh potting mix yearly. Copper fungicides, Neem oil. Avoid overhead watering. Pull and destroy the plant, select resistant varieties next year. Good news is that the organism does not overwinter in our area. Infection can be slowed by removing infected sections of the plant. Avoid overhead watering. Remove infected foliage as it appears, clean tools before moving to another plant. Plant tomatoes in a different area of the garden next year. Copper fungicides, Neem oil. Avoid overhead watering.
Chemical Treatment Early season – Regalia During season – Gavel, chlorotalonil, mancozeb Early season (proactive) - Daconil, Bonide Fung-onil, Late season (reactive) - Ortho Multi-Purpose Fungicide Early season – Regalia During season – Gavel, chlorotalonil, mancozeb, Ortho Copper Fungicide

 

More Information

Vegetable Gardening: Recommendations for Home Gardeners in Pennsylvania

Early Blight and Septoria Leaf Spot on Tomato

Tomato-Potato Late Blight in the Home Garden

Contact Information

Steven Johnson
  • Penn State Master Gardener, Bucks County