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

Leaves

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 (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

• Powdery mildew – humid type from Oidium lycopersicum

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

• Phosphorous deficiency

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

Stem/Trunk

Flowers

Fruit

• 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

Roots