Biocontrol of grey mould by Ulocladium atrum applied at different flower and fruit stages of strawberry

Grey mould is an important disease of strawberries resulting from flower and fruit infection by Botrytis cinerea Pers. The saprophytic fungus Ulocladium atrum Preuss is a promising biological control agent for control of B. cinerea in strawberry and other crops. The objective of this research was to determine the efficacy of U. atrum to control grey mould by a single application of a spore suspension (2 x 10(6) conidia/ml) at different flower and fruit development stages. Four experiments were carried out in 1999, two under natural and two under enhanced inoculum levels of B. cinerea. In each experiment, flowers and young fruits in six distinct stages of development were sprayed with either water or U. atrum suspension. U. atrum suppressed B. cinerea sporulation on petals by 15 to 54%. One to four days after spraying, U. atrum was present on less than 30% of stamens and did not affect the incidence of B. cinerea on these flower parts. The efficacy of the U. atrum sprays in controlling grey mould was low to moderate, and resulted on average in a reduction of 21% in disease incidence on ripe fruits. Low control efficacy was probably due to poor coverage with or colonisation of stamens by U. atrum spores, and a relatively low level of suppression of the colonisation of flower parts by B. cinerea. Significant reductions of grey mould in comparison to the control (p less than or equal to 0.10; on average 41% reduction) were found most frequently when the antagonist was introduced at late flowering or early fruit stages. Therefore, these are the most suitable stages to apply U. atrum. Further studies are needed to improve the spray coverage and persistence of U. atrum inoculum.