My tomato plants are getting some odd discoloration on the tips of young leaves at the top of the plant. (See picture below)

I use a commercial potting mix (perlite and peat mostly) that I amended with a tbs of garden lime and slow release fertilizer. I also use a 10-10-10 water soluble fertilizer once every 2 weeks (1/2 tbs per gallon).
The plants are quite large and my first thought is that they have become root bound.

Fruit production does not seem to have been affected.

They are in 10 gal Rubbermaid containers on top of a roof in NYC.

Identification

Circular to angular spots with dark, concentric rings (target spots) develop on the older foliage
Severe infections spread to younger leaves
Lesions become quite large and are often associated with considerable leaf yellowing
Fruit infections are not common, but may appear as a blackened area at the stem-end
Often Confused With
Bacterial Canker (Early blight may cause browning of leaf edges, similar in appearance, but a lighter brown than bacterial canker symptoms.)
Septoria Leaf Spot (Early blight lesions grow much larger than Septoria lesions.)

Period of Activity
Early blight overwinters in infected crop residue. Spores are present throughout the growing season and may be carried long distances in the wind. Temperatures of 17- 24�C (63- 75�F) and extended leaf wetness favour early blight development.

Scouting Notes
Early blight lesions can be distinguished from other lesions on the foliage by the presence of concentric rings.

Thresholds
Where available use the TOMcast program. If this is unavailable, begin a preventative spray program when the first fruits are about walnut size. Repeat sprays as necessary. Repeat at 5- 7 day intervals during continuous moist weather. Extend the schedule to 12- 14 days in warm, dry weather if diseases are under control. Applications should continue until close to harvest.

Advanced
Scientific Name
Alternaria solani

Identification
The first signs of disease often appear deep in the canopy where the leaves stay wet. Lesions first appear on leaves as dark brown to black spots, 8- 13 mm (5/16- 1/2 in.) in size, on older foliage, but can grow much larger. Spots are circular to angular with dark concentric rings (target spot). The tissue surrounding the spot may be yellow. Lesions become quite large and are often associated with considerable leaf yellowing.

If the disease is severe, lesions also appear on younger leaves. As lesions enlarge, their shape may become irregular. They are often bordered by leaf veins.

Early blight may cause browning of leaf edges. Lesions may coalesce to form large dead areas on the leaf. Lesions may also appear on stems and blossoms (a cause of blossom drop).

Fruit infection is uncommon, showing up as a blackened area, similar in appearance to blossom-end rot, but at the stem end of the fruit. Fruit symptoms are most common late in the season, especially when extended wet periods occur at harvest.

Often Confused With
Bacterial Canker (Early blight may cause browning of leaf edges, similar in appearance, but a lighter brown than bacterial canker symptoms.)
Septoria Leaf Spot (Early blight lesions grow much larger than Septoria lesions.)

Biology
The fungus that causes early blight survive on decayed plant material in soil and can be seed borne. It is spread by wind.

Period of Activity
Early blight overwinters in infected crop residue. Spores are present throughout the growing season and may be carried long distances in the wind. Temperatures of 17- 24�C (63- 75�F) and extended leaf wetness favour early blight development. Unless the fungus is present on transplants, lesions generally don�t show up until flowering.

Scouting Notes
Early blight lesions can be distinguished from other lesions on the foliage by the presence of concentric rings.

Thresholds
Where available use the TOMcast program. If this is unavailable, begin a preventative spray program when the first fruits are about walnut size. Repeat sprays as necessary. Repeat at 5- 7 day intervals during continuous moist weather. Extend the schedule to 12- 14 days in warm, dry weather if diseases are under control. Application should continue until close to harvest.

Management Notes

Reduce early blight inoculum by following a 3 to 4 year crop rotation.
Ensure transplants are healthy and free of disease.
Cultivars vary in tolerance to early blight.
Overhead irrigation can promote foliar fungal disease due to longer periods of leaf wetness.

nycgarden it would be great if you could let me know how those leaves progress.. I'm interested in knowing what happens if you don't snip those off

earley blight lesions can be distinguished from other lesions on the foliage by the presence of concentric rings.

What I hope is that my plants have gotten so big, in terms of the pots that they are in, that the roots of the new shoots at the top of the plant are getting suffocated.

I'll take a closer look today to see if I can see concentric circles and report back. Thanks for all of the advice. I will certainly be cleaning my pots and tools with the bleach solution just in case.

Thanks for your replies.

is it getiing worse or staying neutral?
if worse this would be my second thought.

Yellow, uneven splotches on the leaves. Dead leaves that remain on the plant. Dead areas can be surrounded by a yellow circle.
No damage to stems evident.

Powdery Mildew, a fungus that infects weeds and crops in the solanaceous family.
Occurs late in the season.

Any thoughts on the idea that it may be due to root bound plant that has outgrown its container?

I'll limit the fert. for now to see if that has any effect.

Thanks,