Transfer by infested soil has been confirmed as the main route that the disease lettuce Fusarium wilt is spread, according to a recently published technical review.
Since limited effective control options are available, the review concludes that good hygiene across the supply chain remains the industry’s best chance at controlling this potentially damaging disease.
Infested soil can be spread on farm equipment, trays, pallets, plants and footwear.
AHDB commissioned University of Warwick to collate and review all currently available knowledge on the disease in response to the first UK outbreak, confirmed in October 2017.
Kim Parker, AHDB Crop Protection Scientist, said: “The report identified that there are limited control options for growers, which stresses just how vital good hygiene practices are to prevent disease outbreaks. These need to be implemented before any symptoms are seen; it is important that the industry acts now.”
Andy Taylor, author of the technical review at the University of Warwick, said: “Quaternary ammonium compounds are the most effective disinfectants against Fusarium oxysporum. However, many disinfectants are less effective in the presence of soil.
“Trays and pallets moved between growers and propagators need to be thoroughly cleaned of soil and plant material to enable disinfectants to be effective.”
The lettuce wilt outbreak confirmed in the UK last year was caused by Fusarium oxysporum f. sp. lactucae and identified as race 4 (FOL4), the same pathogen causing serious challenges to protected lettuce production in the Netherlands and Belgium.
While there is some resistance in outdoor lettuce types to FOL4, no indoor butterhead cultivars are resistant, although breeding work is in progress.
If an outbreak of lettuce FOL4 is suspected, removal of crop debris and soil disinfestation before re-cropping is a priority.
Some fungicides and biological control agents that may have some effect against the disease, and that are currently approved for use on lettuce in the UK, are also identified in the report.
SCEPTREplus, AHDB’s crop protection research programme, will conduct a trial in 2018 to investigate the efficacy of new and alternative biological and chemical control options for FOL4. Trials will consider mode and timing of applications.
The full technical review is available to read at https://horticulture.ahdb.org.uk/lettuce-fusarium-wilt-and-root-rot