Science Into Practice - Fungicides for bulb dips

The narcissus industry is facing increasing levels of basal rot in bulbs, but growers rely on just chlorothalonil and thiabendazole to improve hot-water treatments.

In HDC project BOF 074, new fungicides suppressed growth of basal rot pathogen Fusarium oxysporum f. sp. narcissi on agar. The most promising were Mirage (prochloraz) and Orius (tebuconazole). Project BOF 074a was commissioned to see how effective the products were when used in hot-water treatment.

Mirage and Orius were assessed as a dip treatment for curative activity against Fusarium-infected bulbs and compared to Bravo (chlorothalonil) and Storite (thiabendazole). To test their protectant activity, treated narcissus bulbs were planted into a growing medium inoculated with the pathogen and disease symptoms recorded on both foliage and bulbs.

Three triazole fungicides not included in BOF 074 were tested for their ability to reduce growth of isolates of F. oxysprum f. sp. narcissi on agar. Bravo, Orius and Mirage reduced basal rot development in a narcissus bulb stock with an initial high disease incidence but Storite had no effect.

Orius, Mirage and Storite gave good control in hot-water treated bulbs planted in the inoculated growing medium, with Orius being most effective.

The three triazole fungicides reduced growth of the isolates at all concentrations tested compared with where no treatments had been applied. One treatment had greater activity at levels comparable with the most effective fungicides tested in BOF 074. The HDC is considering off-label approvals for products with prochloraz and tebuconazole.

Horticultural Development Company

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