Narcissus and Daffodil

86 G.R. Hanks
On sloping sites, ground cover crops (cereals, grass or oilseed rape) successfully
prevented soil erosion if sown immediately after bulb planting and killed before
crop emergence, provided the growing season was long enough (ADAS, 1987).
Planting in nets
The technique of planting bulbs in netting was developed as an aid to bulb recovery
in heavier soils (Bijl, 1990). In small-scale trials in the UK, the use of netting
did not reduce bulb yields in ‘Tête-à-Tête’, compared with growing bulbs loose
(ADAS, 1988b).
Operations in the field
This section covers the control of weeds, diseases and pests as well as flower cropping
or de-heading, irrigation, roguing and inspection, and (for two-year-down
growing) maintenance of the crop between the two growing seasons.
Weed control
Bulb growers generally aim for good weed control in order to prevent competition,
clean up crops between the two growing seasons, and to assist harvesting
(weeds can clog lifting machinery). The use of crop covers (such as straw) may be a
way of reducing reliance on herbicides.
The effects of weed competition on narcissus yield were examined by Lawson
(1971, 1976) and Lawson and Wiseman (1972, 1976, 1978). Even when weed
cover was substantial, weeds had little effect on early spring growth and first-year
flowering. However, when they resulted in shading during the period of rapid
bulb growth, leaves and stems grew longer at the expense of bulb yield; shading
from late-June had no such effect. Narcissus foliage senesced quicker on weedy
plots, reducing bulb yields, but if weeds were killed late in the season the narcissus
foliage lodged. Over-wintering weeds that grew up with the narcissus foliage were
most damaging, producing smaller, less vigorous bulbs. Under weedy conditions
bulb yield losses approached 20%, or 35% in very dry conditions. Poor weed control
often relates to failure to control a relatively few resistant species (Wood and
Howick, 1958; Lawson and Wiseman, 1972). It is possible that over-wintering
weeds may help the crop by giving winter protection and conserving moisture
(Lawson, 1971), although this aspect has not been researched. Weeds can also
lower soil temperature at bulb depth by 4 °C, compared with a weed-free plot,
which may affect the development of base rot (Tompsett, 1980a).
Herbicides are used at four stages: (1) contact herbicides are used in autumn/
winter before crop emergence; (2) pre-crop-emergence residual herbicides are
used as late as possible before crop emergence; (3) early-post-emergence residual
herbicides are used, usually before shoots are about 10 cm tall; (4) a late-season
herbicide may be used after flowering, although the materials available are
restricted and application at this stage is difficult because the crop foliage has often
flopped to shield the soil surface by this time. The post-flowering period is difficult
for weed control, because the previous herbicide ‘seal’ on the soil surface may be
broken by the feet of flower pickers, and also because the new flower initials are