TIPBURN SYMPTOMS IN LETTUCE
Till last year a surplus of transpiration as compared with the water uptake has generally been considered as the main cause of tipburn. The symptoms were severe on soils with a high salt concentration.
It appeared afterwards that different tipburn symptoms occur which do not have necessarily the same cause. These symptoms are more or less severe in the different seasons.
Therefore it is worthwhile to mention briefly the types of lettuce growing during the year, to be followed by a discussion about the tipburn symptoms which could be distinguished till now. Lettuce growing is a year-round-production.
Under glass lettuce is harvested from October till June and in the open from May till the end of October. In April and May there is also some frame-lettuce.
Till now the following tipburn symptoms could be distinguished.
I emphasize the fact that the different symptoms can occur in every season. However, the frequence of occurrence depends on the season.
Much work has still to be done on the environmental conditions promoting and preventing tipburn and on the anatomical changes in the lettuce leaves.