2.1.3: Parse Error in Logs

After upgrading to 2.1.3 I'm seeing the following error reported in the logs on my test VM:

{:timestamp=>"2016-04-28T08:09:37.070000+0100", :message=>"JSON parse failure. Falling back to plain-text", :error=>#<LogStash::Json::ParserError: Unrecognized token 'INFO': was expecting 'null', 'true', 'false' or NaN
at [Source: [B@5a181f9; line: 1, column: 6]>, :data=>"INFO [AntiEntropyStage:1] 2016-04-28 08:09:32,290 Validator.java:257 - [repair #27f934a0-0d10-11e6-9d09-4d1537ee238d] Sending completed merkle tree to / for keyspace/schemaversion", :level=>:error}

These messages are coming in via the beats input. We have a mix of json formatted and unstructured logs, like this cassandra log line. We know this is the case and, for the time being, are ok with that. Can I disable the logging of these parsing errors as they're causing disk volumes to fill?