I'll also attach an example of the brown spotting that occurs in the centers of adult leaves. The plant is sitting indoors, partial shade during the morning sun. Could I be over or under watering? Is fertilizing the issue? Could this be something fungal? Maybe the metal cage is rusting in the soil and having some unpleasant affect on the plant? Thank you dearly for any help. I love this plant and would hate to see it go downhill! This post was edited by ahyom on Wed, Sep 18, 13 at 12:12

Once the cane turns black it's dead. It needs to be removed. If you look at the roots on that cane you'll see there are no white feeder roots left. All those black roots have died. You need those live white feeder roots for the plant to live. The rest of the plant does look green and seems to have a lot of leaves. The soil looks a little dry to me. I would give some extra water and keep it continuously moist and see if that helps. Also maybe some partial shade during the hottest part of the day.

There are many very humid areas of the USA where people successfully grow tomatoes. The real issue IMO is how often it rains. If it rains almost every day, it's hard to keep fungicide on the plants. Maybe look into disease-resistant hybrids like Iron Lady, Defiant, Mountain Magic, etc., spray them regularly, and time planting for the driest part of the year? Organic copper is a standby for many organic tomato growers. I find that alternating with Serenade (Bacillus subtilis) works well for me in my garden, but I don't know how it will do in yours. I know a lot of gardeners in humid areas here will also use a very dilute bleach spray to control mold as well. The important thing is to spray before disease arrives. Organic fungicides can do a lot to prevent disease and delay its progress, but they are not systemic so cannot cure anything once the plants are affected. I don't want to encourage you to waste your time and garden space if it really is impossible to grow without cover, though, since I obviously have no first hand experience with growing in your conditions. Perhaps setting up a kind of high tunnel or something or a greenhouse if you can is the best--but even then, you will probably need to use fungicide. Growing under cover eliminates the issue of rain, but disease spores still get into these environments. And no matter where you grow, tomatoes are just a really disease prone crop. It's just that excluding the rain means you don't have to spray as much or as often.

I agree it's almost certainly over-watering; and, it's common for the symptoms to appear first in the portion of the variegation that has the least amount of pigment. There are some tricks that employ simple science, and they will help you help you deal with the excess water retention until you can repot into a more appropriate medium. This should help. Also, this is particularly useful when your planting is small and manageable: Newton's First Law of Motion Under conventional container culture, it's a given that saturated/partially saturated media rob roots of the oxygen they need to function normally and efficiently. At best, soil saturation robs your plants of immense measure of potential in areas like growth, appearance, yields, ….. At worst, plants unable to cope with the strain of drought stress caused by saturated media will succumb to it. This isn't a 'scare tactic, it's a very simple and straightforward observation that will be difficult to disagree with a straight face. Newton's First Law of Motion states that an object will remain either at rest, or in motion at a uniform rate and in a straight line unless acted upon by an external offsetting force. In this case, we will designate the 'object' as excess water in your potting medium. At risk of my being redundant, the 'law' can be seen as a simple statement about inertia, that objects will remain in motion and in a straight line unless a force acts to change the motion. To put the law to work for you/your plantings, you should water to beyond the point of total soil saturation - so the medium has been completely saturated and at least 15-20% of the water you have applied has exited the pot. Unless your soil is purposefully constructed to eliminate all/nearly all excess water, it's extremely probable, when the pot has stopped draining, there will be too much water in the potting medium for the plants' liking. To eliminate this excess water: immediately after a thorough watering, hold the pot in one hand over the sink, lawn, or over-sleeping significant other and move it downward, then sharply reverse the direction to upward. You'll immediately note that a good measure of 'excess' water will “continue downward in a straight line” and exit the drain hole. The sharper the reversal of direction, the more water exits the drain hole. When you have repeated the exercise until water no longer exits the drain hole on the reversal of direction, you will have eliminated all excess water and your plants will regard you with a newfound sense of awe. Al