A temporary water shortage, brought on by extra bright light, possibly also excess heat and sunburn.

Likely you didn't harden them off enough before they got full sunlight.

If so individual spots won't enlarge, but more can develop.

Hello desertfarmerjohn,

Me too. I have spots on my leaves that look identical to those shown in your photos on essentially all of my tomato plants; varieties : TOV, Match, Bliss, Cheresita, and unknown Cherry, plus on two varieties of pepper plants. I know of one other greenhouse in the area that is experiencing the same necrotic spots, but to a very minor extent.
Some of the plants have been place for less than two weeks and others have been producing for over a year. All plants are in a small green house, in rock wool and during day light they are drip fed every 30 to 40 minutes and ~65 ml/feeding, depending on the time of year. Recently, the temperature ranges from 55 at night to 85 F during the day. The greenhouse is located in Tucson, so there is no lack of sunshine, but the plants are shaded with 50% white cloth.
The plants were either started from seed or cuttings or were excess stock from a hydroponics operation at a University. In general, the plants look healthy except for the spots.

Although I have had insect problems, the spots are not associated with attack by insects, unless the insects are invisible at 30X and greater.

This adnormality has not had an obvious--to me--effect on production, but IÂm just entering my second year of attempting to grow crops hydroponically.

Note: I have photos, but I haven't figured out how insert them.

So, I am very curious as to what is causing these necrotic spots, and obviously IÂm looking for a treatment. I'm looking for input.

dennyg

Looks like a demoblast problem. If a liquid such as water sticks to the leaf and the sun is bright, the liquid will boil causing the mesophyll cells to die. If you mist or overhead water this could be the source of the problem.

Thanks for the advice. The plants seem to be doing fine now. They are growing rapidly with no additional brown spots on the newer leaves. I had hardened them off for about a week before setting them out and always try to avoid wetting the leaves....but who knows. Anyhow, just glad it wasn't something worse.

Generally, necrotic spots are the result of a phosphorus deficiency (see the following website: http://5e.plantphys.net/article.php?ch=t&id=289 )

Just add a fertilizer like Fish Meal (usually 3-16-0) or else something like Jobe's Tomato Spikes (usually a 5-18-5 mix). The middle number of the three refers to the amount of soluable phosphorus in the mixture. To get the "elemental" phosphorus, multiple by .43 --- lots of phosphorus is needed (along with good wind--in order to polinate the crops-- and the right amount of water) to grow great tomatoes.