Plant Doctor Archive

Grapes in decline

I GROW grapes in a small greenhouse. Two years ago bunches of flowers started drying out from the beginning of the flowering period until most of them dried out completely. The leaves were not affected at all. Last year I had a very good crop with no problems. But this year it is back again. Can you help?

THE splits in the stems of the bunches you sent indicate adverse environmental conditions are probably the cause rather than disease. In a small glasshouse during spring you often get quite dramatic changes in temperature when the weather can change from dull and cloudy one minute to bright sun the next. And the temperature can also drop quite low on cool spring nights.

Fluctuations in water, such as the soil drying out or being excessively wet on occasions, could also contribute to the problem. Try to ensure your greenhouse is well ventilated to prevent it getting too hot during the day - apply a light coat of shading paint if necessary.

Try to maintain even soil moisture. Don't allow the soil to dry out, but also try to prevent seepage, from heavy rain outside, percolating through into the greenhouse soil which can create wet soil conditions. Some commercial grape growers have drains around their greenhouses to prevent this.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.