Narcissus and Daffodil

74 G.R. Hanks
Figure 4.3 Modern front-loading hot-water treatment tanks. Two four-tonne units
with overhead slave tank for holding dip when loading and unloading
bulbs (Photograph: Lyn Secker, Secker Welding, Holbeach).
for bulb producers. HWT tanks can also be utilised for sterilising bulb containers
and other equipment, and other produce requiring dipping in pesticide may
make use of them at ambient temperatures. HWT of narcissus bulbs may be carried
out under contract, but in UK it is usual for bulb growers to treat their own bulbs.
The correct timing of HWT involves the overall logistics of the farming operation.
To minimize crop damage, narcissus bulbs are treated after all flower initials
have been formed and are visible under a hand-lens on dissection of the bud, but
before the root initials have developed too far (shown by the roots erupting from
the base plate). The internal stage of development (ISD) of ‘complete flower differentiation’,
called ‘Stage Pc’ by bulb growers from the paracorolla (trumpet or
cup), the last formed part of the flower bud, is illustrated in Preece and Morrison
(1963), Cremer et al. (1974) and ADAS (1990b). In practice, this means that in the
UK, for example, bulbs should be treated from late-July onwards, aiming to complete
HWT before the end of August, a window of some four weeks. HWT tank
capacity should be calculated to suit this treatment window and the cultivars grown.
Narcissus cultivars which produce fine or early roots (Poeticus, Cyclamineus and
Jonquilla cultivars) should be given HWT first (Benczur, 1976), while for mainstream
cultivars the accepted order is small-cup, large-cup, then trumpet cultivars,
although earlier HWT will give better control of base rot (ADAS, 1974; Millar,
1976; Price and Briggs, 1976). There should be a gap of at least a week between
removal of offsets and HWT, as recent offset removal can increase infection, especially
in certain cultivars (Kruyer, 1978). Bulbs re-claimed from forcing may be
given HWT early, in May or June (Vreeburg and Korsuize, 1991). Where flower
quality is unimportant, an earlier start to HWT may be acceptable, although the
critical development stages or earliest dates for avoiding damage to leaf initials has