Management of strawberry grey mould using mixtures of biocontrol agents with different mechanisms of action

Experiments were conducted using combinations of commercially available biological control agents (BCAs) to control infection of detached strawberry leaves by Botrytis cinerea Pers.;Fr. Combinations were tested either as mixtures, or as sequential treatments before and after disease loading. Five BCAs were initially tested, giving a range of mechanisms of antagonism. Only three (Sentinel, Serenade and Trianum) were effective in single agent experiments and were taken forward for combinatorial tests. Biocontrol efficacies, relative to the control, varied considerably among replicate trials, but all treatments involving Sentinel (BCA: Trichoderma atroviride P. Karsten LC52) and Trianum (BCA: Trichoderma harzianum Rifai T22) were very effective, either in sequential combination with other BCA or alone. Serenade (BCA: Bacillus subtilis (Ehrenberg) Cohn) was least effective, and sometimes did not result in any significant reduction in disease. Combinations of BCAs as mixtures resulted in less control (i.e., higher disease) than when the most effective BCA within the combination was applied alone, indicating possible antagonism between the BCAs. However, when two BCAs were applied sequentially about 48 h apart, there was no strong evidence for antagonism between the BCAs; this was also confirmed in an experiment using whole plants in controlled environment cabinets. We conclude that there was usually no benefit in applying two BCAs either together or sequentially, so in general we would not advise combinations as the method of choice. Thus, research is necessary to investigate possible interference among specific BCAs, since several BCAs may be applied simultaneously under field conditions to control several diseases.