Narcissus and Daffodil

90 G.R. Hanks
bulb growth, especially in April-May when rapid growth is taking place, and it also
improves soil conditions for bulb lifting. Excessive irrigation late in the growing
season (late-May onwards) may increase bulb weight but may delay the ‘ripening’
of the bulb, as well as causing split scales due to uneven growth (ADAS, 1970).
Benefits of irrigation were demonstrated in trials in New Zealand (McIntosh and
Allen, 1992).
Roguing and selection
When grown as ornamentals it is important to inspect crops and physically remove
rogue cultivars and other off-types, but whatever narcissus are grown for they
should be inspected for signs of stem nematode lesions (‘spickels’), disease ‘primaries’
(such as smoulder) and virus symptoms. Affected plants should be removed
and destroyed. Roguing is a skilled and labor-intensive operation: traditionally,
affected bulbs were dug out with a ‘roguing iron’ inserted into the ridge under the
bulb. Various methods of roguing using herbicides (e.g., paraquat or glyphosate
guns, gloves, sticks or aerosol sprays) have been tried (Millar, 1977, 1979; Ryan
et al., 1979; Bijl, 1981). To reduce the spread of viruses, crops should be inspected
regularly: although severe infestations may be seen early in the season, some
symptoms become evident only later. Virus spread is proportional to the number
of infected plants, so this must be kept at a low level by roguing. In a three-year
period, 16, 46 and 90% of healthy plants became infected in plots with initial
infector levels of 10, 20 and 50%, respectively (Haasis, 1939; Broadbent et al.,
1962). Improved stocks (called ‘greenstocks’) can be built-up through vigorous
roguing and by selecting the largest bulbs (ADAS, 1978) or plants with the desired
characteristics (Chen et al., 1988).
Crop inspection
Where narcissus bulbs are to be sold for growing-on commercially, they may need
to be inspected and certified by the appropriate plant health authority. In the UK,
growing season inspections are carried out by PHSI to ensure freedom from stem
nematode. Checking for freedom from other pests and diseases is the responsibility
of the grower.
Operations between growing seasons
During the summer between the two growing years, crops may be re-ridged to
maintain good conditions around the bulbs, to remove dried bulb foliage and to
seal the soil surface. It is important that all crop foliage is removed and the soil
surface is cultivated to close cracks, so that contact or translocated herbicides
subsequently applied do not reach and damage the bulbs (de Rooy and Koster,
1978; ADAS, 1987). It is not clear whether there are implications of re-ridging for
disease control: Millar (1978, 1979) reported that the effects of re-ridging on neck
rot and smoulder were variable, and Melville (1980) reported that, although leaf
debris is a prime source of infection by smoulder, burning debris did not control
the disease. Waterlogged furrows could assist the spread of stem nematode, which
can move up to 1 m in a year, so, where the furrows have been, or are liable to