EFFECTIVENESS OF BULB DIP FUNGICIDE TREATMENTS IN CONTROLLING NECK ROT ON DAFFODILS

Abstract

Smoulder, caused by Botrytis narcissicola, is a disease that sporadically occurs in most commercial daffodil (Narcissus pseudonarcissus) fields in the US Pacific Northwest. Normally this pathogen attacks the foliage, but under certain conditions it can also infect the bulbs where it causes a neck rot. In some cases, bulbs are given a pre-planting fungicide bulb dip to help control smoulder. A trial was conducted on an infested stock of ‘Dutch Master’ daffodil bulbs to determine the effectiveness of several fungicides in controlling smoulder. Bulbs were dipped in each of nine fungicide solutions or water alone (checks) for 20 min at 13.4°C, allowed to air-dry overnight at 23-25°C, and planted into plastic bulb crates for forcing. In early March, crates with rooted bulbs were placed in a greenhouse that was maintained at a temperature of 15.5°C/10.0°C. Disease pressure was high during this test. Symptoms were evident on almost half of the check bulbs and plants. Dipping bulbs in Pageant (boscalid+pyraclostrobin) at 1.31 to 2.62 g a.i./L, Medallion 50WP (fludioxonil) at 0.15 g a.i./L and the combination of Mertect 340F (thiabendazole) at 1.15 g a.i./L plus Captan 50W (captan) at 6.0 g a.i./L significantly reduced the amount of neck rot and leaf necrosis. Although Heritage 50WP (azoxystrobin) and Compass 50W (trifloxystrobin) at 0.15 g a.i./L reduced disease development compared to the checks, they were not as effective as the previous fungicides. Bulb dips in Insignia 20WP (pyraclostrobin) at 0.6 to 1.2 g a.i./L had no effect on disease development. Based on the results of this trial, growers could reduce the amount of fungicide needed to control smoulder by switching from the standard combination treatment of Mertect plus Captan, to either Pageant or Medallion.