Pests, Diseases & Problems of Tomatoes – by Symptom

Whole Plant

Plant has poor vigor and reduced yields

  • Root knot nematode (foliage will also yellow and turn brown from the bottom up; may also look wilted


Yellowing of lower leaves between veins (veins remain green)

  • magnesium deficiency (could be caused by overwatering, which locks up the magnesium in the soil)

Irregular yellow blotches on tomato leaves

  • Tomato leaf with powdery mildew

    Tomato leaf with powdery mildew (UC Davis – IPM)

    Powdery mildew – dry type from Leveillula taurica

Leaves yellowish and slightly curled

  • some leaves and fruit have shiny spots, others may appear blackened; clouds of small white insects fly up when plant is moved; tiny oval yellowish-green scale-like bodies are fastened to the leaf underside = Whiteflies

Powdery white spots on top side of leaves

Bronze or oily brown-colored lower leaves (and stems) gradually moving higher on plant

  • Lower leaves dry and drop from the plant; extreme cases leaves fall off – Tomato Russet Mite

Leaf veins turn purple and bronze, leaves curl upward and feel thick & leathery or brittle

  • Curly top virus 
  • some tomato varieties naturally roll their leaves upward even when they are healthy

Purple leaves

Leaves curling downward

  • look on the underside of the leaves; colonies of small green to pinkish insects (or black) = aphids 
    • Aphids are not a problem unless very heavily infested – which can stunt the plant
    • Also, honeydew from the aphids can be annoying, especially if black sooty mold grows from the honeydew




  • cracking = irregular water & heat
  • sunscald = irregular water & heat
  • matchstick tomatoes
  • blotchy ripening = low potassium availablity
  • bitter tasting tomatoes
    • Tomatoes receiving standard nutrition (100%) were compared with enhanced nutrition (150%). The enhanced nutrition treatment was found to have a significant positive effect on tomato quality, color, and acceptability (Better Crops)
    • low potassium:
      • caused by not enough present, too much water or a pH drop (low pH inhibits potassium uptake)
      • K is the essential element for tomato to produce sugar
      • of all of the essential elements, soil K content most affects the total acid content in the fruit (flavor) (Better Crops)
    • low sulfur
    • low boron
    • low sodium
    • not enough sunlight (too much shade) – 
      • Sunlight has the most profound effect of all of the environmental factors on tomato sugar concentration (Better Crops)
    • cool temperatures may also unsweeten fruit


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