Integrated disease management for narcissus

Foliar sprays of fungicides are the cornerstone for management of the main diseases of narcissus. However it is best to take a combined management approach. Here’s a guide to an integrated approach to managing disease.

The information was last updated in 2016.

Foliar sprays of fungicides are the cornerstone for management of the main diseases.

And as some fungicides also delay foliar dieback you may also reap the rewards of increased bulb yields even in the absence of significant levels of foliar disease.

But managing hygiene and hot water treatment are important too. 

Disease management advice

• If you are uncertain of the cause of premature leaf dieback, have a sample examined for Peyronellaea curtisii (leaf scorch), Botrytis narcissicola (smoulder) and Ramularia vallisumbrosae (white mould).
• Assess the risk of foliar diseases, for example, from cultivar stock history, production location, field topography, disease occurrence in the crop the previous season, whether flowers were cropped the previous season and recent weather.
• Apply preventative foliar sprays where there is a high disease risk, especially of leaf scorch or white mould.
• Use fungicides from at least two different fungicide groups to minimise the risk of selecting fungicide resistant strains.
• Monitor occurrence of foliar diseases to inform fungicide product choice and spray interval.
• Monitor carefully for white mould after periods of cool (5–10°C), wet (12–24 hours’ leaf wetness) weather; these conditions being particularly favourable to infection by R. vallisumbrosae.
• For crops where flowers will be harvested the following year, consider applying one or more sprays of products that control foliar diseases, delay senescence, and increase flower yield, such as Signum or Vivid. Note that some fungicides delay senescence even in the absence of foliar disease.
• Where early lifting or an autumn herbicide treatment is required, do not apply a late spray of a fungicide that delays leaf dieback.

Resistant cultivars

Choice of cultivar greatly affects the risk of damaging attacks from leaf scorch and white mould; but smoulder is less affected by cultivar.

Utilising knowledge of cultivar susceptibility is helpful when the number of spray days is restricted because of rain or wind.

Leaf scorch is most often worst on Poeticus, Polyanthus, Poetaz and Tazetta types, although most varieties can be attacked when conditions favour the disease.

Recent observations

Recent observations indicate Israeli Paperwhites are more prone to infection than some others.

The Tazetta variety Innisidgen is reported as most susceptible to leaf scorch, followed by Sols varieties (also the most likely to show early dieback in spring).

Some other flower crops in the family Amaryllidaceae have also been recorded as hosts of leaf scorch, including Amaryllis, Galanthus and Nerine.

Damaging

White mould is especially damaging on late-flowering cultivars such as Cheerfulness, although some early and maincrop cultivars including California, Dutch Master, Planet and Hollywood can be severely affected.

With smoulder, experimental work showed that Golden Harvest was more susceptible than Dutch Master, with Cheerfulness and King Alfred intermediate.

Grower observations have noted damaging attacks in cultivars Golden Harvest, Tamara, Planet and Tamsyn in recent years.

Hot water treatment (HWT)

Historically, HWT, including the use of formalin, has been shown to greatly decrease infection by P. curtisii (leaf scorch) and B. narcissicola (smoulder) in bulbs. Smoulder was rarely a problem where bulbs were lifted and treated annually.

Although formalin is no longer permitted as a hot-water dip additive, it is considered likely that HWT alone (three hours at 44.4°C) will reduce bulb infection by P. curtisii and B. narcissicola to some degree.

The effect of current fungicides and biocides, added to the hot water tank for control of stem and bulb eelworm (Ditylenchus dipsaci) and basal rot (Fusarium oxysporum f. sp. narcissi), on the viability of B. narcissicola and P. curtisii in bulbs is unknown.

Sanitation

Roguing infected plants and removal of crop debris are logical approaches for reducing disease pressure.

However, where examined for reduction of smoulder they have not proved reliably effective in reducing disease levels.

Furthermore, they involve considerable labour inputs, which are increasingly expensive or unavailable.

Rotation of narcissus with non-susceptible crops for five to six years is strongly recommended for management of basal rot. Such rotations will likely greatly reduce the persistence of R. vallisumbrosae and P. curtisii in the soil.

Debris risk

Because of the risk of debris and soil blowing from one field to the next, it is recommended that, where possible, new plantings should not be adjacent to current crops or fields where narcissus crops were grown the previous year.

Tractors, spray machinery and boots should also be washed between crops, especially after work in a crop obviously affected by one or more of the foliar diseases.

Roguing of infected plants and removal of crop debris may be practical and contribute to disease management where a cultivar is grown on a very limited scale, such as a display area.

Please note this information was last updates in 2016. The majority of the content and recommendations remain pertinent to commercial Narcissus production, but some of the biocidal and plant protection products mentioned may no longer be approved for use on narcissus.

Biocidal and plant protection products must only be used in accordance with the authorised conditions of use. Regular changes occur in the authorisation status of biocides and plant protection products. For the most up to date information, please check with your professional supplier, BASIS registered adviser or the Chemical Regulation Division (CRD) of HSE (https://www.hse.gov.uk/crd/) before use.

While the Agriculture and Horticulture Development Board seeks to ensure that the information outlined on this page is accurate at the time of publishing, no warranty is given in respect thereof and, to the maximum extent permitted by law the Agriculture and Horticulture Development Board accepts no liability for loss, damage or injury howsoever caused (including that caused by negligence) or suffered directly or indirectly in relation to information and opinions contained in or omitted from this information.