Narcissus and Daffodil

78 G.R. Hanks
can also be prevented, but without the need to pre-soak bulbs or to use a treatment
temperature higher than 44.4 °C. By this means (sometimes called ‘partial
pre-warming’), the window for the safe HWT of narcissus bulbs in eastern England
can be extended to late-September (Hanks, 1995a). An equivalent treatment of
1 week at 20 °C is recommended in some Dutch advisory material.
There is a difference in Dutch and UK advice on the warm-storage of earlylifted
bulbs known to be infected with stem nematode. The former suggests a warmstorage
of at least one week at 30 °C after lifting, while in the UK it is stated that
pre-warming should be avoided because of the danger of inducing the formation
of ‘wool’ if the bulbs are allowed to dry out.
Bulb treatment after HWT
The increasing practice in UK is to plant bulbs soon after HWT, which means they
can be planted while still damp. This avoids the need for re-drying and storage
and reduces handling, but it means that the bulbs are planted into relatively warm
soil in August, possibly encouraging base rot. When removed from the HWT tank,
the bulbs should be allowed to drain and then should be cooled, ventilated and
surface dried using fans in a drying wall or similar arrangement. Although there is
no evidence from trials to show a distinct benefit from rapid cooling to ambient
temperatures after HWT (Tompsett, 1973), this seems sensible. From the viewpoint
of operator safety, the ventilation of bulb handling areas is critical, especially
when bulbs are being removed from the HWT tanks and moved to the drying
facility. As an alternative to immediate planting, bulbs can be dried after HWT,
followed by appropriate storage and replanting in September, when soil temperatures
have fallen sufficiently to slow the development of base rot. In this case,
rapid drying is important in controlling base rot (Hawker, 1935, 1940).
Other pre-planting pesticide applications
The application of insecticides, other than in HWT, has been evaluated for the
control of large narcissus fly. Separate pre-planting dips of chlorpyrifos were less
effective than using the material in HWT (Tones and Tompsett, 1990). One-hour
dips, either immediately after lifting or before planting, were evaluated by Bogatko
(1988) and Bogatko and Mynett (1990): several insecticides were found to be
effective in controlling larvae (including isofenphos and carbofuran).
Bulb storage treatments to manipulate growth
In addition to the considerations relating to bulb storage generally, storage
temperatures may be altered, in the period before planting, to manipulate the
subsequent growth of the crop. This was investigated by Rasmussen (1976b), who
compared the growth of narcissus bulbs after storage at ambient outdoor temperatures
and planting bulbs in September, with storage at 20 or 23 °C and planting in
October. Emergence, but not anthesis or senescence, was delayed by controlledtemperature
storage and later planting. Better yields of bulbs or flowers resulted
from using the higher temperatures, such that best results were obtained from the
ambient regime in warm winters and from 23 °C storage in cool winters. More