Bulletin 208, Cucumber Diseases in Florida


 Fig. 30. Ring spot of cucumber leaf, produced by sunburning through
water drops.
amination showed that this spotting was more prevalent on ex-
posed leaves. Whereas leaves partially covered showed spots on
only the exposed area. Leaves fully protected though mature
showed no spots. It was first thought that overhead irrigation
was responsible but this theory was disproved, as non-irrigated
fields showed the same spotting. All fields in the vicinity of
Gainesville were affected.
 A search of the rainfall records showed that one-tenth of an
inch of precipitation was recorded at 2 o'clock in the afternoon
of a slightly cloudy day with maximum temperature of 87
degrees. This occurred four days prior to these observations. To
judge from these circumstances it seems quite probable that the
spots were caused by the sunshine following the rain, the rain
drops acting as lenses, killing the host cells in specific lines,
making this characteristic marking on the leaves. All the various