Need to control particular source while accessing particular URL when URL forwarding enabled for multiple applications on the Same Virtual server

Simply iRule assigned to the Virtual Server would do it:

when HTTP_REQUEST {
    if {[HTTP::host] == "app2.test.com" && [IP::addr [IP::client_addr] equals 10.10.10.100]} {
        drop
    }
}

Could also look to do the same with an LTM Policy:

ltm policy ExampleDropPolicy {
    controls { forwarding }
    requires { http tcp }
    rules {
        dropTraffic {
            actions {
                0 {
                    forward
                    reset
                }
            }
            conditions {
                0 {
                    tcp
                    address
                    matches
                    values { 10.10.10.10 }
                }
                1 {
                    http-host
                    host
                    values { app2.test.com }
                }
            }
        }
    }
    strategy first-match
}