顶烧是一种叶类作物（最常见的是莴苣）的生理性病害，其特征是内层叶片的边缘和尖端变成棕色并死亡。它不是由营养液中缺乏钙引起的，而是由于致密、封闭的叶球内部蒸腾作用不足，导致钙运输不足引起的。
关键事实
- Caused by calcium deficiency at the leaf tip — calcium transport requires transpiration
- Common in fast-growing, densely headed lettuces: butterhead, romaine, Boston types
- Occurs even when reservoir calcium levels are adequate
- Triggered by low VPD, high humidity, and insufficient airflow across the canopy
- Prevention: increase airflow, reduce humidity, space plants wider, use oscillating fans
- Some lettuce varieties are genetically tip-burn resistant — choose these for dense systems