Blackspot is an a serious disease threat with no complete fungicide solution, and is now as serious as mildew or botrytis. 'Outdoor growers and producers of everbearer strawberries are at high risk,' said Berrie.

Bblackspot spores have more opportunity to spread infection during wet weather and under extended harvesting conditions. The fungus can show no symptoms until harvest when, under warm, wet favourable conditions, it can destroy a crop. No fungicide offers complete control, said Berrie.

'Get weeds under control, critically, before they emerge. Waiting to control weeds and using a contact herbicide can act to stimulate sporulation and disease spread, she warns. In the UK, 35 weed species that commonly occur in strawberry crops can symptomlessly be infected with the blackspot fungus Colletotrichum acutatum,' she said.

Herbicides such as paraquat and glyphosate encourage the fungus to sporulate as it's displaced from the former weed host. A pre-emergence residual herbicide such as Dacthal (chlorthal-dimethyl) provides good control of a broad spectrum of weeds from before they even emerge, right through the season. This removes potential hosts for the fungus before they exist.

Berrie said blackspot is a rising threat that will persist on strawberry land. 'It is commonly brought in on infected planting material, but detection is difficult.' She recommends cultural and hygiene measures to support a good herbicide programme with fungicides employed only as a last resort.

'Spore masses are sticky and slimy, aiding their spread. For example, they can remain viable on denim jeans for up to five weeks. Staff visiting fields should pay particular attention to hygiene and equipment should be clean and disinfected regularly. Growers can reduce water splash by using straw mulches between rows and by covering with a plastic mulch. Field activities should be minimised when the crop is wet and where there's a known infection. Picking operations should be managed to ensure all rotted and over-ripe fruit is regularly removed,' she advised.

Where fungicides are used, products containing different active ingredients should be applied alternately. In trials, products such as Amistar (azoxystrobin), Frupica (mepanipyrim) and Elvaron Multi (tolyfluanid) have shown good levels of disease control.

However, Berrie noted that few fungicides are particularly effective under warm, wet conditions.

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