Not enough Magnesium in your soil. Magnesium ions are essential in chlorophyll, the 'pigment' that gives leaves their green coloration and thus also their light absorbing properties.
Common fertilizer should do the trick, but heres my trick: Depending on the size of your plant give the soil some cranberry juice. Does the trick. I know it sounds odd but my plant's leaves were yellowing, I added cranberry juice (rich in magnesium) to the soil and 10 days later the yellowed leaves reversed to bright lush green...I did not add any fertilizer etc. during this period. Just water and one quarter glass of magnesium.
Or instead of cranberry juice try Epsom Salt which can be purchased at Wal-Mart, CVS, Walgreens or any store like these mentioned for relatively cheap.
In agriculture and gardening, magnesium sulfate is used to correct magnesium deficiency in soil, since magnesium is an essential element in the chlorophyll molecule. It is most commonly applied to potted plants, or to magnesium-hungry crops, such as potatoes, roses, tomatoes, peppers and cannabis. The advantage of magnesium sulfate over other magnesium soil amendments (such as dolomitic lime) is its high solubility.**
**Quote from http://en.wikipedia.org/wiki/Magnesium_sulfate#Applications
well bad news usuall this means bacterial spot or bacterial speck.
the leaves start to die from the bottom and move up eventually killing the plant. you will get to harvest tomatoes but not as much as healthy non infected plants. this infection is a fungal disease caused by water or rain hitting the soil and bouncing up so its called a soil born disease. you can't stop the disease but it can be put in check and slowed down with a fungicide. Best to find disease tollerant type. rotate plants, 4 to6 inches of mulch or solorize soil (till area,wet area well, cover with 4mil clear plastic secure with stones brick ect and let the hot sun bring the soil up to at lease 120 degrees F hoter is better do this for a couple of days then plant and use mulch
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Lack of iron in the dirt. Esp if using container planting. can be bought and applied at garden store.
Tomatoes need EPSOM SALTS to the soil when they start to bud out. Get a bag and read the instructions. Magnesium is so important to the growth and FLAVOR. And also keeps bottom rot away.
Over watering or underwatering.Also, calcium and blood meal use is assumed when planting.
It could be something as simple as a lack of nitrogen in your soil.
When tomato plants leaves turn yellow, it could be from a fungus or bacterial problem.If this is the case, you will want to treat this according to your garden center instructions. They have treatments for this type of thing, and you need to follow the directions carefully so as to prevent killing your tomato plants. If the entire plant wilts quickly, and you know the moisture is adequate, you have one of the wilt diseases or root-knot nematodes, and the plant must be destroyed immediately to protect the rest of your tomato crop.
The most likely cause is tomato blight.
It really is awful to see a full crop ripening and then suddenly succumb to blight, where the plant and the fruit turn black and die in a matter of days.
If this happens to your plants, you must gather up every trace of the plants and fruit and burn them. Don't compost them.
Blight will survive in the soil, so don't plant next years tomatoes or potatoes in the same spot. Potatoes belong to the same family as tomatoes and share many diseases.
Plant next years crop as far from the infected site as you can and consider growing the plants under cover.
It is called blossom end rot. It can be attributed to lack of calcium in the soil and irregular water availability.
leaving it out to much
ionakd
Heat causes living cells turn red.
Starch.
Rusting
Mold
keep charging i had ds bottom screen turn black
Gravitation.
on 9th page :-) near the bottom of the page "the others said of squealer that he could turn black into white"
Brake dust!
Bugs are wiping their asses on them
Alkaptonuria is an inherited condition that causes urine to turn black when exposed to air.
Too much iron in the water
It is the high temp and the high return Pressure inside the injector that causes the fuel To turn black