downy mildew of alfalfa

例句：

1. 1.The farmers are worried about the downy mildew of alfalfa affecting their crops.
   农民们担心苜蓿的霉病会影响他们的庄稼。
2. 2. The disease is spread by wind and water, making it difficult to control.
   这种病害通过风和水传播，很难控制。
3. 3. To prevent the downy mildew of alfalfa, farmers must maintain good crop rotation.
   为了防止苜蓿的霉病，农民必须保持良好的作物轮作。