Garden Pests and Diseases: Tomatos - root rot ?, 1 by Percnco

Percnco wrote:
10% of crop dead/ dying. Starts with a yellowing of the lower leaves, wilting, then falls over dead- presumably as the living tissue at the bottom of the stem has rotted away.
Very sandy, Perth basin soil. with a bit of organic matter but not enough. Water goes straight through, so water logging not a problem. Neither is compaction.
Very alkaline soil 8-8 5. Not ideal.

Help much appreciated. What is it? How to stop and prevent?

Thankyou