JasperReports uses the Jakarta Commons Logging API.
Commons Logging has a discovery mechanism that connects to logging API you are using in your project.
You need to configure logger named "net.sf.jasperreports" in your logging configuration file to control the logging level of JasperReports.
If you are using Log4j, you can read this section of there documentation for exact details.
For example you may write something like this in log4j.properties file
log4j.logger.net.sf.jasperreports=INFO, Daily
Where "Daily" is name of an appender configured in same properties file.