Narcissus and Daffodil

94 G.R. Hanks
methods have been tested, in which lighter, infected bulbs generally tend to float,
albeit with some apparently healthy bulbs (Anon., 1980; Tompsett, 1976); because
such a procedure could itself spread disease, if used HWT should follow promptly.
Bulb drying in the field
Bulbs may be elevated to the surface and left there to dry for several days. In suitable
situations (in a dry, windy climate) the method is widely used and is successful,
although there are several disadvantages. Drying is clearly dependent on
weather, bulbs can be attacked by moulds or can re-root if conditions are damp,
they are liable to sun scorch, and a reliable supply of labor is needed to pick up
bulbs. When harvesting bulbs in this way, a post-lifting spray cannot conveniently
be applied, although some growers are known to spray fungicide over the bulbs as
they are lifted and deposited on the surface.
Post-lifting cleaning and fungicide application
Narcissus bulbs should progress rapidly from the field to drying. When bulbs are
being handled in bulk containers (½- or 1-tonne bins), rapid transfer to the drying
area is easy, but it does not allow soil removal, breaking up clumps of bulbs or an
on-line fungicide application, although bulbs in bulk bins may conveniently
receive an immediate dip treatment (in formaldehyde) before drying. When bulbs
are harvested in loose bulk in trailers, they can be unloaded and passed along a
series of lines, which could involve vibrating riddles and a rotating barrel riddle,
for separation, soil removal and fungicide spray application en route to the store.
Mechanised lifting can result in a high clod and stone content, and fluidised bed
separators may be used to separate bulbs from soil (Zaltzman et al., 1985). Some
preliminary bulb grading may be needed at this stage in certain operations.
Narcissus bulbs are not usually washed to remove soil, because of the danger of
increasing bulb rots, but the method may be used where bulbs are lifted under wet
conditions from ‘sticky’ soils.
In the case of cultivars susceptible to base rot, a prompt dip or spray treatment
is highly beneficial. The benefits of a post-lifting cold dip in formaldehyde have
been well demonstrated (e.g., Hawker, 1935; ADAS, 1973; Millar, 1978, 1979). A
fungicide may be added to the formaldehyde in bulb dips. Benzimidazole fungicides
(thiabendazole, benomyl) were investigated as bulb dips by Gould and Miller
(1970, 1971a,b), replacing the mercurial fungicide used earlier and which could
be phytotoxic (Gould et al., 1961; Miller and Gould, 1967). A treatment of
1000ppm thiabendazole for 30 minutes at 25 °C one day after lifting was found to
be very effective. Current recommendations in the UK are for a 15 minute dip in
thiabendazole and formaldehyde at ambient temperatures, within a day of lifting
bulbs. Dip treatments impose an extra burden on bulb drying and require the
disposal of spent dips. Spray treatments are more economical, and several fungicides
are effective used in this way (Hanks, 1994b), but the number of fungicides
approved for such use is limited; in the UK thiabendazole is used. Thiabendazole
sprays are usually applied via simple arrangements of conventional spray nozzles
at a convenient point in the line, but ultrasonic and electrostatic sprayers have
also been used effectively to give a more even or targeted spray (G.R. Hanks,