Anne Wade, of Clyde, asks :-

My husband is very disappointed with the tomato plants in our glasshouse this year. He has lost 9 (all moneymaker) so far and they were about a metre tall, some with tomatoes about the size of a golfball. We have been growing tomatoes for 26 years in the glasshouse and never had any trouble before. The soil was changed and brought in from the vege garden as usual. About 3 weeks ago some of the leaves were wilting then we noticed that the stem was rotting. An insect was in the stem. What is the problem and how could he prevent it happening again.

Robert Hill, a plant pathologist at Lincoln University's Bio-Protection Research Centre, responded.

It is difficult to see from the photographs exactly what the disease problem is but Botrytis cinerea may well be the cause. I have worked with Botrytis for many years, including the tomato crop. In this case my guess is that there was a combination of factors leading to the problem. Serious damage from an insect would aggravate Botrytis infection under the right conditions (cool with high humidity). Our work was focused on the conditions (especially relative humidity and temperature) that favoured Botrytis and on biological control options using other fungi. Our two papers on this subject in Plant Pathology (1996 p276-284 and p795-806 give more technical details.

I recall one serious incident involving Botrytis in table grapes grown under glass where the problem was eliminated by reducing the relative humidity in the glasshouse to below 90%.

What I think has happened in this case is that there has been insect damage which has then allowed the fungus to enter the plant. Conditions in the greenhouse probably favoured disease development. It would be wise to remove and burn all affected plant material.

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