Narcissus and Daffodil

72 G.R. Hanks
bulbs with base rot) can be safely spread on bulb fields, according to Dutch trials
(van Dijk, 1990). Narcissus growing produces 3–5m3 /ha of waste from the field or
1 t/ha from bulb forcing (Bouma, 1990). Care should be exercised in applying
plant wastes from processing to cropping land, because of the possible effects of
residual solvents present.
Pre-planting bulb treatments
Following the receipt of bulbs, the main treatments to be considered before planting
are storage and hot-water treatment (HWT). In all bulb handling operations, a
reasonable standard of hygiene should be maintained, particularly of containers,
bulb stores and equipment, as soil and other debris can be a major source of stem
nematode, bulb scale mite, and fungal propagules. Nematode ‘wool’ (the dehydrated
fourth stage juvenile stage of the stem nematode) can survive for 25 years
in its dry state. For use at room temperature, phenols (including cresylic acid) and
iodine/phosphoric acid disinfectants were most effective in killing stem nematode
(Lole, 1990). Alternatively, bins, etc., can be treated in HWT tanks for 10 minutes
at 50 °C. Stored bulbs can be fumigated by specialist contractors with methyl
bromide to control bulb scale mite, without phytotoxicity (Gurney and Gandy,
1974; Murdoch, 1975; Powell, 1977).
Bulb storage – general
Ideally, bulbs should be stored after receipt at 17–18 °C in a controlled-temperature
store with good air movement, some exchange of fresh air, and a relative humidity
below 75%. Temperatures below 17 °C slow shoot development, and high temperatures
will encourage base rot. In practice, bulbs are often stored outdoors (in
which case they should be protected from sun and rain) or in sheds at about ambient
temperatures. If stored in bulb trays, air circulation may be adequate; if stored
in loose bulk or in bulk bins, it will be necessary to maintain some air movement
through the bulbs, through ducts or fans, to prevent dampness which could lead
to premature rooting and fungal growth. Roots of narcissus bulbs form over a
short time and emerge simultaneously, so if they grow in storage and are broken
at planting, this damage can be serious (Rees, 1972). When narcissus roots were
repeatedly excised (up to four times), new roots developed from the base plate,
but their number was progressively reduced and, increasingly, plants failed to
flower (Yasuda and Fuji, 1963).
Hot-water treatment (HWT)
HWT is the key aspect of growing narcissus bulbs, and its practice is described in
Gratwick and Southey (1986) and ADAS (1985b). It is essential to apply HWT
(colloquially called ‘sterilising’ in the UK) to all narcissus planting stocks to control
stem nematode, and other pests are also killed by HWT. It is important to use
HWT even if bulb stocks have no history of stem nematode, as very few nematodes
are needed in a bulb to cause its destruction (Hesling, 1971), while the treatment
of stem nematodes at sub-lethal temperatures can result in only temporary inactivation
(Hastings et al., 1952). Early experiments on the HWT of narcissus were