The Influence of Calcium on the Development of Lettuce Tipburn1

Foliar sprays of Ca(NO 3 ) 2 or CaCl 2 completely controlled lettuce tipburn in the variety ‘Meikoningen’ when directed to susceptible immature leaves. Analysis of treated and untreated plants showed that treatment markedly increased the Ca content of tipburn susceptible leaves and revealed a 5-fold increase in Ca content as one progressed from immature heart leaves to mature basal leaves in untreated plants. Foliar sprays of organic acid salts, particularly oxalate, accelerated the development of tipburn and increased its severity. When Ca and oxalate treatments were alternated, application of Ca at the beginning of the dark period and oxalate in the morning resulted in markedly less tipburn than application of these sprays in the reverse order.