Science into practice Narcissus: overcoming soil sickness

In the Isles of Scilly, limited amounts of land reduce the options for crop rotation so Narcissus, which has been grown as a commercial crop for more than a hundred years, may have been cropped on the best sites almost continuously.

As a result, a build up of pathogenic organisms produces a problem of poor growth or "unthrifty" crops known as soil sickness.

Growers wanted to find out the extent and causes of soil sickness and how to overcome it. HDC project BOF 50 tested 20 unthrifty crops and 11 were found to test positive for the two organisms associated with soil sickness in Narcissus - the free-living soil nematode Pratylenchus penetrans and the root-rotting fungus nectria. In 2003, two affected sites were selected for long-term replicated trials (BOF 50a) to compare standard treatments with planting biofumigant crops.

After good Dutch results of nematode control by growing Tagetes patula 'Ground Control', this technique was compared with injecting Telone II (dichlopropene) and a combination of the two. Growing the biofumigant crop requires land to be set aside for a year, whereas Telone II requires only three weeks. Currently Telone cannot be used and its approval is being reviewed later this year.

Following treatment, N. Royal Connection was planted in 2004 and the trial plots monitored for five years - the usual crop duration in Scilly. Treatments applied to only one of the two sites produced consistently better growth over five years than the untreated areas. The best treatment was the combination of growing Tagetes followed by Telone, but both when used alone gave measurable increases in crop vigour, senescence, bulb numbers, bulb size and total weight.

Horticultural Development Company

- For details on all HDC activities, visit www.hdc.org.uk.


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