June 2010. A farmer in Trinidad used to grow good crops of lettuce using hydroponics, but after a number of crops, the roots turned black and the planted started dying. What could be the cause, and what is the remedy?

There was a general consensus that the problem was due to fungi, perhaps Pythium or Fusarium contaminating the recirculating system, but they would need to be plated out for a definite identification. The problem, however, would seem to be contamination of the nutrient solution, so attending to that would probably solve the problem irrespective of the pathogen.

The efficient hydroponics system in Jamaica use an inert ???soil??? of perlite and, importantly, after each cycle of planting and harvest, the perlite and the whole system is sanitised with a solution of hydrogen peroxide, which appears to prevent problems.

There are a number of websites that may help:

1) betterbuyhydroponics.com/index.php – saying that Pythium is the worse disease problem! and

2) Pythium root rot is a problem:

www.rootrotrebound.com.au/root_rot_treatment.php

Here the writer, who is selling Rebound, suggests adding it to the reservoir each week. Rebound contains metalaxyl. This is good against Pythium and also Phytophthora, which is also a cause of root rot. However, it is expensive.

Also, use calcium hypoclorite to clean the system – when plants are not there, of course!

Interesting problem, but it seems that good sanitation is the way to go, especially if the grower is producing for an organic market, and fungicides can’t be used. So, it comes back to rigorous cleaning between crops.