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Posted by Rosemoor Garden on 14 Sep 2009 at 01:37 PM

For the last few years we have suffered from blight on our glasshouse tomatoes. Prior to that it was very unusual to get blight in the house. It appeared this year on the 6th August. There are supposed to be more aggressive strains of blight around now and this could be the cause of our problem.

Also the last three wet summers must have increased the incidence of a Beaumont Period. Infection by blight spores can only occur when the temperature does not fall below 10degrees C and the relative humidity does not fall below 75% for 48 hours. This is called a Beaumont Period. When these conditions occur any blight spores in the air will germinate on the leaves of the plant.

When it first appeared we were devastated and thought we would lose all the crop in a few weeks so we stopped all damping down to reduce humidity and ventilated the house as much as possible. This seemed to slow the spread of the disease between the plants and we were able to keep the crop going till the end of the season. The drier atmosphere has caused some problem with “dry set” on the fruit but it is a price worth paying to keep the crop going.

The blight first appears on the leaves and can spread to the stem.


Surprisingly, although the stem is affected it appears to only be on the surface and does not stop the plant growing and feeding the fruit.

We have always got blight on the outdoor tomatoes. It normally appears around early July and wipes the crop out in a few weeks. Even ‘resistant’ cultivars such as Ferline eventually succumb. In a bad year we don’t even get the first truss to ripen on the normal cultivars but the very early ones such as Tumbler, Red Alert and Totem are early enough to give a decent crop before the blight strikes.

So if blight strikes your glasshouse tomatoes all is not lost. With a bit of care you may be able to keep them going till the end of the season.

Garry Preston, Fruit & Vegetable Gardener


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on 14 Sep 2009 at 03:29 PM

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