Narcissus and Daffodil

Production of Narcissus bulbs 91
become, waterlogged, it is useful to improve drainage by breaking up the soil with
a single tine in early-August, when roots will not be damaged.
Bulb lifting
Lifting date
Traditionally, bulb crops were lifted, once, most (95%) of the foliage had died
down, in July in the UK. This maximizes yield and ensures that bulbs are ‘mature’,
with well developed outer skins, when lifted. One disadvantage is that bulbs then
remain in the ground when soil temperatures are increasing, encouraging diseases
such as base rot: infection occurs late in the growing season, when moribund
roots are present (Hawker, 1935, 1943). McClellan (1952) reported that infection
with the base rot pathogen was related to soil temperature, occurring only above
13 °C and reaching a maximum of 29 °C. Further, when bulbs are lifted at this
time it may not be possible to dry, clean and grade bulbs and meet sales deadlines
or produce bulbs for early forcing. Early lifting, overcomes these problems, and
may be useful in pest avoidance: for example, the larvae of the large narcissus fly
hatch and invade bulbs late in the growing season (June), while if foliage is
allowed to senesce naturally, a three-fold increase in virus levels occurs (Mowat,
1980a). For these reasons, but mainly to have bulbs ready for the export market, it
is usual in the UK to lift bulbs from early-June onwards, before foliage senescence
is well advanced, which requires the foliage to be removed prior to lifting. When
growing bulbs for processing, other considerations may apply, but bulb lifting is
possible over a window of at least two months. If lifting is delayed when the soil
is moist, there is a danger of bulbs re-rooting before lifting. Very late bulb lifting
may also mean that HWT, if necessary, is given well after the ideal date.
When bulbs are lifted early, yields are reduced because photosynthesis and
assimilation have been limited, and the choice of lifting date is a balance between
an acceptable loss of yield and the advantages of early lifting described. After planting,
total plant dry weight falls until March, and this is followed by a period of
rapid weight gain. The curve of growth is sigmoidal, with the linear phase extending
from late-April to early-June (in southern England) (Rees, 1972) (Figure 4.7).
Yield losses are therefore severe if bulbs are harvested before June, as shown, for
example, by the data of Allen (1938) and van der Weijden (1987). Very early lifting
(in May) leads to reduced flower numbers (Allen, 1938; Rees and Hanks,
1984). Reporting a trial on the date of defoliation carried out with a number of
cultivars, Kingdom (1981) stated that removing leaves two weeks after flowering
was very detrimental to yield, after four weeks was adverse but not destructive in
all cultivars, and after six weeks gave results comparable with those of intact controls.
In any case, bulbs should be lifted early if they are known to be infested with
stem nematode, so that they can receive HWT early, and such bulbs should not be
allowed to dry out before HWT because of the likely formation of nematode
‘wool’. Early lifting and HWT also improves the control of base rot.
Where it is desired to maximize yields, and pest and disease considerations are
not significant, there may be advantages of delaying foliar senescence through the
continued use of a fungicide sprays programme. The critical factors controlling
senescence are not known, but it appears to be stimulated by high temperatures,
even when cooler weather follows (Rees, 1972).