Science into practice - Using potassiun bicarbonate for apple mildew

Powdery mildew is a significant apple disease and extremely costly for growers to contain through pruning and routine fungicide application. Potassium bicarbonate has been used as a powdery mildew eradicant on many other crops with huge success.

This crystalline salt is also found in baking powder and fire extinguishers. The powdery mildew pathogen is less likely to develop resistance to potassium bicarbonate than to more specific fungicides due to its mode of action.

Previous trials showed that potassium bicarbonate reduced the incidence of secondary mildew and could be used with sulphur as part of a programme for control post-blossom. HDC project TF 186 set out to assess the physical compatibility of potassium bicarbonate with a range of wetting agents and compared its effectiveness against apple mildew with combinations of products including flowable sulphur and a biopesticide, Sentry S (Bacillus subtilis).

At the recommended rates on the label, there were no compatibility problems with any of the wetting agents tested. Levels of mildew were greatest where no potassium bicarbonate was applied. In the first year (no statistically significant effects were found in the second year), the best control was achieved when potassium bicarbonate was added to Sentry S, which offers protection.

These results were typical of those from other crops, such as strawberry. Potassium bicarbonate has eradicant properties so is useful early in the season to reduce existing levels of the disease. When used with products that have protectant properties, such as biopesticides containing Bacillus subtilis, protection can be maintained into the season.

Horticultural Development Company

For details on all HDC activities, visit www.hdc.org.uk.


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