Posted: 15/11/2012 at 08:29
Thanks for the tips Busy-Lizzie and Geraldineb. Growing tomatoes in a greenhouse certainly makes them less likely to catch blight, as the blight spores are airborne. Covering outdoor tomatoes with a polythene sheet, draped over supports, should have a similar effect.
Do keep those suggestions coming in.
Growing in greenhouses doesn't help against fungal disease, Catherine. Quite the opposite. Yes, the spores are airborne, and they will enter greenhouses. Greenhouses, because of their closed environment, can be incubators for fungal disease. In fact, there are fungal diseases like Leaf Mould that are almost specific to greenhouse tomatoes. You rarely see it on outdoor tomatoes.
Fungal diseases have to be seen pretty much as a fact of life for tomato growers. You can't avoid the spores. Unless you want to spray preventively - which doesn't guarantee against infection, but gives you a head start against it - all you can do is seek to minimise the diseases' impact with sound housekeeping practices:
- Air circulation is the priority. It will help against spores settling on foliage. Keep as much space as is practicable between individual plants and avoid clumps of impenetrable foliage on individual plants by judicious pruning of excess branches and foliage.
- Avoid wetting the foliage at all costs. Damp foliage is an incubator for fungal spores.
- Maintain a gap of at least 1' to 18" between the lowest foliage and the soil. Fungal spores can and will drop from the leaves to the soil underneath and can be splashed back up onto the foliage when watering. The gap helps against this.
- Remove any leaves the moment they show signs of infection. It will help to slow the spread. It won't stop infection because there will be more spores arriving on the breeze.
The reality is that the most common fungal diseases - Early Blight, Septoria Leaf Spot, etc - don't quickly destroy tomato plants. With care, the plants can last the whole season and be typically productive. The nastier diseases - Late Blight, etc - are a different matter. They will wipe out the plant.
I'd also be wary of covering outdoor plants with polythene sheet. It will trap any spores inside and prevent air circulation. The spores will have a picnic.