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Botrytis threat to strawberries

Despite recent low temperatures favouring a slow down in botrytis development, Certis’ Morley Benson is urging strawberry growers to be vigilant as temperatures rise again. 

“The relatively warm winter promoted disease sporulation during January, but while the recent cold snap helped curtail its spread, inoculum has remained,” he warns.

He advises taking measures to pre-empt the fungus Botrytis cinerea before it establishes and infects new growth to avoid an impossible control situation.
“Botrytis cinerea, or grey mould, is one of the top two diseases, along with powdery mildew, faced by protected strawberry crops, and is historically the number one disease for outdoor production,” highlights Morley. 

As a saprophyte Botrytis has the ability to survive within the structure of a young strawberry fruit as a latent infection. “First entering wounded plant tissue through access points created by dead and decaying plant petals, the fungus then develops a spore tube that ensures its survival within the plant until the fruit begins to swell and ripen,” explains Morley.

“Given conducive still and humid conditions, disease sporulation takes place and the infection is visibly expressed as fluffy grey fungal strands around the fruit.

“By this time nothing can be done to rectify the problem. The fruits are inedible causing significant yield loss, and in some instances, death of the entire crown,” he notes.

“Prompt removal of dead and decaying plant material is an effective means of cultural control,” highlights Morley. “But given the levels of inoculum able to initiate infection this spring, it may be necessary to apply a prompt, preventative, fungicide in some cases.

“This is particularly important given the limited options for the curative control of the disease.”

He recommends employing IPM compatible products such as Frupica SC (mepanipyrim) as early as possible.

“For best results two applications of Frupica should be made in a sequence to build up the level of active ingredient on the leaf and guard against infection.

“Applications should be targeted around the petals of the plant before disease entry to prevent access of the disease and development of mould,” he stresses.

Maintaining ventilation and air flow around the plant is also important to prevent a moist, still microclimate developing and favouring the spread of the disease.