阅读下面的诗歌 ，回答相关问题。
                                                                                                                   山 行
                                                                                                          〔清〕 姚 范
                                                                                         百道飞泉喷雨珠，春风窈窕绿蘼芜。
                                                                                         山田水满秧针出，一路斜阳听鹧鸪。
                                                                                      【 注】蘼芜（míwú）：香草名。

国外旅游，严禁从国外带水果等农产品，其原因是（  ）