Although long-distance diagnosis of such a problem
is tricky at best. I will give you several reasons
yellowing of the tomato leaves occurs.
One reason could be Nutrient deficiency.Spray young
plants with a folar application of seaweed extract
(eary morning) and add compost to the soil.Have the
soil tested and amend as neccessary.
If young leaves are yellow with green veins,suspect
iron deficiency.Reduce soil pH to help make iron
more available.If dark spots develop in the yellow
areas,and leaves are small and narrow,the problem
may be zinc deficiency.
If young leaves are pale and tips die, the problem
is calcium deficiency. Add high-calcium lime,dolomite
lime if magnesium is also low,wood ashes,or gypsum
to the soil.
plants that are stunted and have yellow or pale
older leaves may have a nitrogen deficiency.
Young leaves that are mottled with yellow and are
narrow and twisted could be tobacco mosaic virus
(TMV) Destroy diseased
plants.Wash your hands after
handling tobacco and before touching tomato
plants.
Older leaves yellow;shoots or whole
plant wilts
the cause may be Walnut,Fusarium,or Verticillium
wilt.Walnut wilt occurs in soil containing black
walnut roots,which secrete a substance tht is toxic
to many
plants.Tomatoes within 50' of black walnut
will wilt and suddenly die.
Fusarium and Verticillium wilt are both fungal dieases
and are difficult to tell apart.Both wilts begin as a
yellowing and wilt of the lower leaves.
plants are
stunted and do not recover when watered.
Cut open a stem near the soil line and look for
discoloration.Verticillium wilt usally affects
the whole
plant while Fusarium may affect individual
shoots before the whole
plant is affected.
Destory infected
plants.
You can prevent wilt problems by soaking
seeds in
a 10% bleach and 90% water solution.
Leaves are yellow and
plant wilts in hot weather.
the cause may be Root Knot Nematodes.Check roots for
swollen sections or galls up to 1" in dameter.
Destory infected
plant and do not add to compost.
Apply Chitin(Shells of lobsters,crabs,shrimp,and
other shellfish). add to the soil it stimulates
growth of beneficial microorganisms. These microorganisms
produce the enzyme Chitinase, which destroys nematode
eggs and larvae.
I hope this helps.
