Narcissus and Daffodil

88 G.R. Hanks
Insecticide and nematicide applications
In climates where the large narcissus fly is a problem, it is advisable to apply
appropriate insecticides if available. Regular sprays against adult flies should be
applied, preferably making use of pest forecasting models to target applications
accurately (Finch et al., 1990; Collier and Finch, 1992). Suitable insecticides
include omethoate (Conijn, 1990; Conijn and Koster, 1990), sprayed just before or
during the oviposition period. The application of granular and liquid insecticides
to the ridges during the growing season, to target the newly hatched larvae, has
also been used. Many insecticides have been tested, but their effects are not always
consistent each year (Bogatko, 1988; Bogatko and Mynett, 1990; Tones et al.,
1990; Ben-Yarkir et al., 1997).
Foliar applications of oxamyl were evaluated for the control of stem nematode
by Westerdahl et al. (1991) as an alternative to HWT with formaldehyde, preplanting
soil sterilisation with 1,3-dichloropropene, or applying phorate at planting.
Several rates and timings of oxamyl application reduced nematode levels in
bulbs and leaves without any phytotoxicity. Earlier, Bergeson (1955) had applied
three, weekly applications of Systox or other systemic phosphates to narcissus in
pot trials, and reported that nematode numbers in the leaves and bulb were
reduced by these treatments, without toxicity at lower rates.
In the case of high-health status stocks or VT stocks, the regular application of
aphicides should be considered in warmer weather when populations are high.
While aphids only rarely colonize narcissus, several common species spread
viruses during exploratory probings. Frequent applications of anti-feedant insecticides
(pyrethroids) can be used, although Broadbent et al. (1957) showed that
systemic insecticides can increase virus spread, possibly by increasing the irritability
and probing of aphids before death. Alternatively, mineral oil sprays, which
disrupt normal transmission of virus particles, may be applied, although they are
not always effective (Mowat et al., 1984). Mineral oil sprays can, however, reduce
narcissus yield, in one trial by 50% when sprays were applied weekly (ADAS,
1982c). Some dwarf cultivars, such as ‘Tête-à-Tête’ and ‘Hawera’, appear to be
more sensitive to mineral oil sprays (Vreeburg and Korsuize, 1987).
Other chemical treatments
The application of ammonium nitrate sprays can delay leaf senescence and
increase bulb yields, perhaps by replacing the failing uptake from senescent roots
(Rees, 1972). No beneficial effects on bulb yield have been reported from UK trials
in which a range of plant growth regulators (PGR) were applied in the field (ADAS,
1984). However, for N. tazetta, El Sallami (1997) reported a range of effects when
PGR were used as bulb soaks or foliar sprays, including increased bulb production
with ethephon.
Flower cropping and de-heading
Depending on local practices, flowers from narcissus crops are either cropped
routinely, only when market prices make this worthwhile, or not at all if bulb
production is paramount. When grown for processing, it is unlikely that flowers