How to Manage Pests
UC Pest Management Guidelines
Tipburn is characterized by browning of the margins of young, maturing leaves in head and leaf lettuces. The brown area may be limited to a few small spots at or near the leaf margin, or the entire edge of the leaf may be affected. Many pinpoint necrotic areas along the margin may give that tissue a speckled appearance. Brown veins may occur near the brown lesions.
Tipburn is a result of calcium deficiencies in growing tissue although calcium levels in the soil may be adequate. Calcium is important for cell wall strength and membrane integrity. Calcium mostly moves in the transpirational flow in the plant, therefore, the highest concentration is in exposed leaves from which transpiration is occurring. Inner leaves of head lettuce or leaf lettuces transpire less than exposed leaves and are more likely to develop tipburn. Rapid growth creates conditions for the development of tipburn. Head formation reduces transpiration in the inner leaves of iceberg lettuce; low evapotranspiration (ET), which occurs when conditions are foggy, etc., reduces transpiration in leaf lettuces. Soil water stress can also reduce the transport of calcium to the plant. Tipburn is rarely the result of low soil calcium, but more commonly is due to water stress and low ET that causes transient deficiency of calcium in rapidly expanding leaf tissue.
Cultivars vary in their susceptibility to tipburn. In areas and seasons in which tipburn is likely to occur, resistant cultivars could be used. Foliar sprays of calcium have reduced tipburn in studies in which the nutrient is applied directly to the tissue; however, this is ineffective in head lettuce because the nutrient will not reach susceptible tissue deep inside the head in time to prevent the development of tipburn. Calcium fertilizer applications to the soil are generally ineffective because soils in California's lettuce producing districts generally already have sufficient calcium to supply the plant.
UC IPM Pest Management Guidelines: Lettuce