I used Captan on my tomato seeds and started them under a grow light.  They came up great and looked good for about 3 weeks.  Now the leave have started turning yellow.  They are about 4 inches tall and have 4-6 leaves.  Why are they turning yellow?  I suspect it is a watering issue.  How should I water them if that is the problem.  Any help will be appreciated.

Craig,

Anderson, IN

Yes, more light is needed (natural light is best) as is food and some wind to strengthen their tender stems. My suggestion is to begin moving your tomaotes to an outdoor location with filtered natural sunlight, if the day temperatures are warm and mild (bring the plants inside at night until the threat of frost has past). Also, begin to feed them lightly with a fertilizer formulated for tomatoes. Light breeze and filtered natural light will help toughen your tomatoes up for outdoor life. As the plants strengthen, you can move them into full sun.

As an aside, though Captan is a non-systemic fungicide it is not needed for tomato seeds or seedlings. If you are worried about the damping off by Pythium and Phytophthora fungi then try steaming your seed starting medium before planting your seeds. I do this and have never had a problem with damping off. Just put your medium in a baking pan, add some water, mix it a bit until moist, cover with aluminum foil and bake at a low temperature. I usually stream it at 250 degrees Fahrenheit for 20 or 25 minutes. Take it out, keep it covered and allow it to cool before planting. I swear by this method.

As far as over-watering, be sure to allow the plants to dry out a bit between watering. Never subject them to wet soils or standing water.