Leaf spots

摘要

There is no hard and fast way of telling by the naked eye if a leaf spot has a fungal or bacterial origin, although any tiny, dot-like bodies associated with the spots or lesions are fungal spore-bearing structures. Bacterial leaf spots often have water-soaked margins.Leaf spots that appear to have a marked directional or one-sided progression across a plant or a crop, or which affect adjacent but unrelated species, may have a physical cause, such as spray damage. However, some spot diseases show directional spread patterns associated with irrigation sources. White leaf spots or flecks may be caused by hail damage, especially on fleshy-leaved plants or bulbs. On roses, downy mildew also causes black spots on the upper side of the leaf. These tend to develop into angular blotches and do not develop the tiny spore-bearing structures of black spot.