Aims: The aim was to produce and characterize an aerated compost tea (ACT) that suppressed growth of the plant pathogen Botrytis cinerea. Methods and Results: Three different open-windrow composts were sampled weekly from the early secondary mesophilic stage until maturity. Each 10 kg of compost sample was extracted in 30 l of aerated water for 24, 48 or 72 h. Relative to water, all batches of ACT applied to detached bean leaflets reduced lesion development following single-point inoculations of B. cinerea. There was a significant linear, inverse relationship between the internal windrow temperature of compost (< 51 degrees C) used to prepare ACT and the extent of lesion development. Bacterial diversity in ACTs from one windrow was highest using compost sampled at 48 degrees C. The compost weight-to-water volume ratios of 1 : 3, 1 : 10 or 1 : 30, using compost sampled from a fourth windrow at 50 degrees C, also produced ACTs that reduced the growth of B. cinerea on bean leaflets. The '1 : 3' ACT, and to a lesser degree the same ACT filtered to remove micro-organisms, inhibited the germination of B. cinerea conidia. Conclusions: ACT produced using the methods reported here suppressed the growth of B. cinerea on bean leaflets, with an abundant and diverse microbial community likely to contribute to pathogen suppression. Significance and Impact of the Study: This is the first report of the use of immature compost to produce a pathogen-suppressive ACT, suggesting that compost stage is an important production variable.