1. Plant Disease
  2. Host and Disease Descriptions

Tomato (Solanum lycopersicum)-Early Blight

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Latest revision: 
March 2024
Image related to Tomato (Lycopersicon esculentum)-Early Blight
Note not only necrotic areas of fruit but also leaf spots.
Photo by Kathy Merrifield, 1990.

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Potato (Solanum tuberosum) - Early Blight

Cause Alternaria tomatophilai (formerly A. solani), a fungus that may also attack horsenettle, nightshade, and other wild plants related to tomato. The fungus may be on or in seed, but internal infection is rare in seed produced commercially. The fungus can survive on infected plant refuse in soil or overwinter on solanaceous plants. Infection is favored by temperatures of 75°F to 84°F, high moisture, and low soil fertility. The disease is not common in Oregon, particularly west of the Cascade Range.

Symptoms Small, irregular, blackish brown spots usually first appear on older leaves. Spots enlarge to 0.25 to 0.5 inch in diameter, and they commonly show ridged concentric rings in a target pattern. Leaf tissue around the spots turns yellow. If spots are numerous, the entire leaf will be yellowed. Some spotting may be on older leaves early in the season, but the greatest injury usually is as fruit begins to mature. Defoliation may be severe if environmental conditions are favorable, exposing the fruit to sun scald.

Older fruit develop dark, leathery, sunken spots that may be quite large with concentric markings similar to those on diseased leaves. The dark, dry decay may extend some depth into the fruit. Infected mature or immature fruit frequently fall from the plant.

Seedlings may have circular or elongated lesions with concentric markings on the stem, which will girdle the plant. This symptom is known as collar rot.

Cultural control

  • Rotate with nonhost crops for 3 to 4 years. Eradicate weed hosts and volunteer tomato plants.
  • Use pathogen-free seed or transplants.
  • Maintain plant vigor and proper fertilization.
  • Remove and destroy plant debris at year-end. Alternatively, hot compost or incorporate into the soil soon after harvest.
  • Irrigate so that leaves dry fairly quickly.
  • Use pathogen-free soil and equipment in the greenhouse or seedbed.

Chemical control Spray at regular intervals.

  • Bordeaux 8-8-100. H
  • Carboxamide (Group 7) formulations are registered for use. Do not make more than two (2) sequential applications before alternating to a labeled fungicide with a different mode of action.
    • Endura at 2.5 to 3.5 oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
    • Fontelis at 10 to 24 fl oz/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
  • Chlorothalonil formulations (Group M5).
    • Bonide Fung-onil is available for home gardens. H
    • Bravo Ultrex at 1.3 to 1.8 lb/A on 7- to 10-day intervals. 12-hr reentry.
    • Echo 720 at 1.38 to 2 pints/A on 7- to 10-day intervals. Preharvest interval is 0 days. 12-hr reentry.
  • Copper (Group M1) products are not recommended as stand-alone materials.
    • Badge SC at 0.75 to 1.8 pints/A and 0.5 to 1.5 Tbsp/1,000 sq ft in greenhouses on 3- to 10-day intervals. Preharvest interval is 0 days. 24-hr reentry for greenhouse use; 48-hr reentry for all other applications.
    • Champ WG at 1.06 lb/A on 3- to 10-day intervals. 48-hr reentry. O
    • Cueva at 0.5 to 2 gal/100 gal water on 7- to 10-day intervals. May be applied on the day of harvest. 4-hr reentry. O
    • Cuprofix Ultra 40 Disperss at 1.25 to 3 lb/A on 5- to 10-day intervals. 48-hr reentry.
    • Kocide 2000 at 1.5 to 3 lb/A or Kocide 3000 at 0.75 to 1.75 lb/A on 5- to 10-day intervals. 48-hr reentry. O
    • Liqui-Cop at 1 to 3 teaspoons/gal water. H
    • Nu-Cop 50 DF at 1 lb/A for processing tomato and 3.2 lb/A for fresh market tomato on 7- to 10-day intervals. 48-hr reentry. O
    • Previsto at 1 to 2 quarts/A on 5- to 10-day intervals. 48-hr reentry. O
  • Dithane DF Rainshield (Group M3) at 1.5 to 2 lb/A or Dithane F-45 Rainshield at 1.2 to 1.6 quarts/A. Do not apply within 5 days of harvest. 24-hr reentry.
  • Fracture (Group BM01) at 24.4 to 36.6 fl oz/A on 7- to 10-day intervals. Preharvest interval is 1 day. 4-hr reentry.
  • Mettle 125 ME (Group 3) at 6 to 8 fl oz/A on 7- to 14-day intervals. Application can be made the day of harvest. 12-hr reentry.
  • OSO 5% SC (Group 19) at 3.75 to 13 fl oz/A on 7- to 14-day intervals. Can be applied the day of harvest. 4-hr reentry O.
  • Regalia (Group P5) at 1 to 4 quarts/A plus another fungicide on 7- to 10-day intervals. Does not benefit from the addition of an adjuvant. Preharvest interval is 0 days. 4-hr reentry. O
  • Rhyme (Group 3) at 3.5 to 7 fl oz/A. Alternate or tank-mix with a non-Group 3 fungicide for resistance management. Preharvest interval is 0 days. 12-hr reentry.
  • Scala SC (Group 9) at 7 fl oz/A on 7- to 14-day intervals. Use only in a tank-mix with another effective early blight fungicide. Do not apply within 1 day of harvest. 12-hr reentry.
  • Strobilurin fungicides (Group 11) are labeled for use. Do not make more than one (1) application of a Group 11 fungicide before alternating to a labeled fungicide with a different mode of action.
    • Aftershock at 2 to 5.7 fl oz/A. Do not apply within 3 days of harvest. 12-hr reentry.
    • Cabrio EG at 8 to 12 oz/A or at 8 to 12 oz/100 gal spray volume (dilute). Preharvest interval is 0 days. 12-hr reentry.
    • Evito 480 SC at 5.7 fl oz/A. Preharvest interval is 3 days. 12-hr reentry.
    • Flint at 3 fl oz/A. Do not apply within 3 days of harvest. 12-hr reentry.
    • Quadris Flowable at 5 to 6.2 fl oz/A. Do not apply with an adjuvant. May be applied the day of harvest. 4-hr reentry.
    • Reason 500 SC at 5.5 to 8.2 fl oz/A. Do not apply within 14 days of harvest. 12-hr reentry.
  • Trilogy at 0.5% to 1% or Neem Oil 70% at 1%. Trilogy is not labeled for use in Oregon. Do not use above 90°F or when plants are under heat or moisture stress. Do not use when foliage is wet as good coverage is essential. Poor control as a stand-alone product. 4-hr reentry. O
  • Premixes of fungicides are available and offer ease for fungicide resistance management. Do not make more than one (1) application of a Group 11 fungicide before alternating to a labeled fungicide with a different mode of action; for other fungicide groups apply no more than two (2) sequential applications alternating with another fungicide with a different mode of action
    • Aprovia Top (Group 7 + 3) at 10.5 to 13.5 fl oz/A on 7- to 14-day intervals. Can be applied the day of harvest. 12-hr reentry.
    • Dexter Max (Group M3 + 11) at 0.8 to 1.1 lb/A on 7- to 10-day intervals. Preharvest interval is 5 days. 24-hr reentry.
    • Dexter Xcel (Group M3 + 11 +3) at 36 fl oz/A on 7- to 10-day intervals. Preharvest interval is 7 days. 24-hr reentry.
    • Inspire Super (Group 3 + 9) at 16 to 20 fl oz/A on 7- to 10-day intervals. Preharvest interval is 0 day. 12-hr reentry.
    • ManKocide (Group M1 + M3) at 1 to 3 lb/A on 7- to 10-day intervals. Under moderate to severe disease pressure use the higher rate on 3- to 7-day intervals. Do not apply within 5 days of harvest. 48-hr reentry.
    • Miravis Prime (Group 7 + 12) at 9.2 to 11.4 fl oz/A on 7- to 21- day intervals. Preharvest interval is 0 days. 12-hr reentry.
    • Orondis Opti (Group M5 + 49) at 1.75 to 2.5 pints/A on 7- to 14-day intervals. Preharvest interval is 0 days. 12-hr reentry.
    • Priaxor Xemium Brand (Group 7 + 11) at 4 to 8 fl oz/A on 7- to 14-day intervals. Preharvest interval is 0 day. 12-hr reentry.
    • Quadris Opti (Group 11 + M5) at 1.6 pints/A or Quadris Top (Group 11 + 3) at 8 fl oz/A. Preharvest interval is 0 days. 12-hr reentry.
    • Switch (Group 9 + 12) at 11 to 14 oz/A on 7- to 10-day intervals. Do not apply to small tomatoes in the greenhouse. May be applied the day of harvest. 12-hr reentry.
    • Tanos (Group 11 + 27) at 6 to 8 oz/A on 5- to 7-day intervals. Must be tank-mixed with an appropriate fungicide with a different mode of action (non-Group 11 or 27). Do not apply within 3 days of harvest. 12-hr reentry.

Biological control

  • Actinovate AG at 3 to 12 oz/A as a foliar spray on 7- to 14-day intervals. 4-hr reentry. O
  • Actinovate Lawn & Garden at 1/2 to 1 teaspoon/gal water. H O
  • Double Nickel LC at 0.5 to 4.5 pints A on 3- to 10-day intervals. Can be applied the day of harvest. 4-hr reentry. O
  • LifeGard WG (Group P6) at 1 to 4.5 oz/A on 7- to 14-day intervals for activating plant resistance. Refer to label for appropriate rate per application volume. Preharvest interval is 0 days. 4-hr reentry. O
  • Serenade Opti at 14 to 20 oz/A on 5- to 7-day intervals. Applications can be made up to harvest. 4-hr reentry. O
  • Sonata at 2 to 4 quarts/A on 7- to 14-day intervals. Can be applied up to and on the day of harvest. 4-hr reentry. O