ADO NET data source doesn't accept dynamic variable?

Hi, I created an execute sql task to select max(date), then passed the result to a variable, then followed by a data flow which pulls data from ADO SOURCE (ORACLE), I used this variable as parameter in Expressions/Property: ADO NET SOURCE.SqlCommand "select ... from Oracle table where datecolm>to_date (' " +@variable+" ')", but it didn't read as Evaluated value showed ...to_date(' '). the package failed. But if I replace by another variable with hard code value '30-JUL-18', everything works. So my question is if ADO NET source doesn't accept dynamic variable, in this case, which is the result set variable for a sql statement? Is there a way to work around? Thanks!