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New lettuce disease outbreak reported in UK

Staff Writer |
An outbreak of lettuce wilt and root rot caused by F. oxysporum f. sp. lactucae was reported in the UK for the first time in early October at an unconfirmed location.

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The pathogen was identified as Race 4 which is a particularly aggressive strain of the fungus with no known treatment or varietal resistance available to date.

UK propagators and growers are advised to review their production protocols, particularly regarding crop hygiene.

Prompt diagnosis is recommended, so if wilt is suspected at any stage during production, most lettuce breeding companies will test samples for you. Independent diagnostic services are also available at several UK research organisations.

A wilt disease of lettuce caused by Fusarium oxysporum f. sp. lactucae was first described in Japan in 1955.

This disease was then detected in other Asian countries, in the USA and finally in Europe (initially Italy and Portugal, and since confirmed in France, the Netherlands and Belgium).

For over three years, protected lettuce growers in the Netherlands and Belgium have been battling with a particularly aggressive strain of the pathogen known as Race 4. Up until now, the pathogen has been contained in mainland Europe.

In mainland Europe, F. oxysporum f. sp. lactucae is considered as one of the limiting factors for commercial production of lettuce during the summer season. In Italy for example, up to 70% losses in contaminated lettuce fields have been observed.

Under favourable climatic conditions (the optimum soil temperature is between 24-28°C although the disease can occur at temperatures as low as 8°C), infection may lead to total destruction of the crop.

In the Netherlands, some growers have been obliged to stop growing lettuce in infested structures during the summer months.

Disease control is extremely difficult since spores survive for a long time in soil and crop debris, there are no effective fungicides and soil sterilisation has limited efficacy. Therefore, avoidance is the best strategy.

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