EVALUATION OF HOT-WATER TREATMENTS FOR MANAGEMENT OF DITYLENCHUS-DIPSACI AND FUNGI IN DAFFODIL BULBS

Treatment of daffodil (Narcissus pseudonarcissus) bulbs in a 0.37% for maldehyde water solution at 44 (1 for 240 minutes is a standard practi ce in California for management of the stem and bulb nematode, Ditylen chus dipsaci. Recent concern over the safety of formaldehyde and growe rs' requests for a shorter treatment time prompted a reevaluation of t he procedure. The time (Y, in minutes) required to raise the temperatu re at the bulb center from 25 to 44 C was related to bulb circumferenc e (X, in cm) and is described by the linear regression Y = 15 + 3.4X. The time required for 100% mortality of D. dipsaci in vitro without fo rmaldehyde was 150, 60, and 15 minutes at 44, 46, and 48 C, respective ly. Hot water treatment (HWT) with 0.37% formaldehyde at 44 C for 150 minutes controlled D. dipsaci and did not have a detrimental effect on plant growth and flower production. Shorter formaldehyde-HWT of 90, 4 5, and 30 minutes at 46, 48, and 50 C, respectively, controlled D. dip saci but suppressed plant growth and flower production. Fungal genera commonly isolated from the bulbs in association with D. dipsaci were P enicillium sp., Fusarium oxysporum f. sp. narcissi, and Mucor plumbeus , representing 60, 25, and 5%, respectively, of the total fungi isolat ed. These fungi caused severe necrosis in daffodil bulbs. HWT at 44 C for 240 minutes reduced the number of colonies recovered from bulbs. T he effects of formaldehyde, glutaraldehyde. and sodium hypochlorite in reducing the population of fungi within bulbs were variable. Satisfac tory control of D. dipsaci within bulbs can be achieved with HWT of bu lbs at 44 C for 150 minutes with 0.37% formaldehyde or at 44 C for 240 minutes without chemicals.