The effect of treatment with Ulocladium atrum on Botrytis cinerea-attack of geranium (Pelargonium zonale) stock plants and cuttings

In two successive seasons, the effect of treatment of geranium stock plants with the competitive saprophytic fungus Ulocladium atrum as a biocontrol a gent against Botrytis cinerea was compared to a fungicide treatment with Eu parene M. B. cinerea incidence and severity on the stock plants, B. cinerea spore load in the air around stock plants and death of cuttings due to B. cinerea were scored. B. cinerea incidence and severity were much stronger i n the second than the first experiment. This was quantitatively expressed b y higher numbers of conidia of B. cinerea monitored in the second than the first year, both on necrotic (a maximum for the control of 27.5 x 10(6) spo res per sample - all necrotic leaves of five plants - in experiment 1 again st 86 x 10(6) in experiment 2) and green leaves, but numbers of conidia of B. cinerea recovered from the air were only slightly different. The death r ate of cuttings was moderate in the first and extremely high in the second experiment. For the fungicide treatment, maximum sample values of 7% and 76 % of 6-week old cuttings were killed in the first and the second experiment respectively. Treatment with U. atrum was effective in reducing all parame ters studied. With the exception of the spore load of B. cinerea in the air and the success of cuttings, the effect of U. atrum varied from as good as the fungicide to half as effective. In the first trial, only Euparene M re duced spore load in the air, in the second trial only U. atrum consistently did so. In the first trial U. atrum reduced death of 4-week old cuttings, though less than fungicide (1.2, 20 and 38% killed with fungicide treatment , U. atrum treatment and control respectively). In the second trial only th e fungicide reduced loss of cuttings. The impact of the data on the integra tion of U. atrum in a control system of B. cinerea in geranium is discussed .