Controlling plant and fruit diseases in strawberry fields

Abstract

Grey mould and stem-end rot affect the strawberry industry in Australia. Losses of 10% of the crop are equivalent to a loss of $46 million across the different growing areas. The effect of different fungicides on the control of grey mould and stem-end rot affecting ‘Festival’ strawberry plants was studied in south-east Queensland over three years. This work followed recent changes to the use pattern for the multi-site fungicides thiram and captan, which can now be used more regularly than previously in Australia. There was a restriction on the use of captan with no more than five sprays allowed in a season. Thiram could be used only up to the first flowering. A program based on captan and thiram along with several single-site fungicides during wet weather controlled grey mould and stem-end rot. These treatments in turn provided high marketable yields.
Applications of a plant-defence promoter, plant extracts, organic acids, fatty acids, a salt, four bacteria, and a fungus were not as successful as the standard program, even when the soft fungicides were applied alternately with thiram and captan. The plant-defence promoter acibenzolar-S-methyl, organic acids, B. subtilus (strain QST 713), B. amyloliquefaciens and potassium bicarbonate gave intermediate control. In contrast, B. subtilus (strain MBI 600), Streptomyces lydicus, Trichoderma harzianum, potassium salts of fatty acids, and two plant extracts were ineffective. A strategy based on thiram and captan applied alternately, with the addition of single-site fungicides during wet weather provided the best control of disease, with 3 to 4% losses. Control plots had losses of 25 to 38%.
The soft chemicals were less effective than the programs based on captan, thiram and single-site fungicides. The use of the thiram and captan in rotation with other fungicides from different chemical groups in wet weather will reduce the risk of fungicide resistance and extend the useful life of registered products. This strategy has not been available to growers previously.