Allotment Gardening Advice Help Chat

Growing => Growing in Greenhouses & Polytunnels => Topic started by: Bernard on April 10, 2011, 16:57

Title: Mildew in the new greenhouse
Post by: Bernard on April 10, 2011, 16:57
Re problem of seedlings dying via what appears to be powdery mildew -

Replaced my old 6x6 greenhouse last autumn with a 6x8. Changed to double walled polycarbonate. I always plant in soil borders so exchanged soil with several areas of the garden and dug in some garden compost, not very well rotted. I have done this in previous years in the old greenhouse.

Have grown tomatoes from seed for 20 years without trouble. My first crop of radishes has for years been from the edges of the greenhouse border, also a few lettuce. Never any trouble.

This year, radish seed sown in the border germinated in  but never got to true leaf stage, they turned white and withered away. The same happened with a T&M salad leaf mixture.

Then my tomato seedlings growing in cells which I put in the greenhouse during the days only started to look sickly, white on the seed leaves apparently being powdery mildew. They have stopped growing, seed leaves have already withered and true leaves appear to be following.

A general question-
any ideas as to why this should happen?

A specific question -
polycarbonate is reputed to block UV. Could this allow moulds to flourish?

On the the hand, if UV were effectively blocked fluorescent colours would not fluoresce - but they do, so perhaps the UV blocking is not very effective.