ASHS 2025 Conference

Lettuce (Lactuca sativa) tipburn is a calcium-related physiological disorder that affects enclosed young leaves, leading to browning, necrosis, and curling of leaf margins and reduced marketability. While greenhouse vertical airflow fans (VAFs) have been proven effective at controlling tipburn, they have not been widely adopted due to cumbersome installation, sunlight obstruction, and electricity consumption. Recent research showed that a calcium-mobilizing biostimulant, when added to the nutrient solution, mitigated tipburn in greenhouse hydroponic lettuce by enhancing calcium mobility. However, how it compared to VAFs was unknown. We investigated the effects of this biostimulant and VAFs on lettuce tipburn and growth in a greenhouse hydroponic system during summer. Seedlings of lettuce ‘Rex’ were propagated indoors and, on day 14, transplanted into deep-water-culture trays in a climate-controlled greenhouse. In a split-plot randomized complete block design with two blocks, plants were subject to six treatments per block: three biostimulant concentrations (0, 0.25, and 0.5 mL⋅L–1) with and without VAFs promoting vertical airflow at ≈1 m⋅s–1. Plants were sampled on 14, 21, and 28 days after transplant (DAT). Compared to plants without the biostimulant or VAFs that progressively exhibited severe tipburn, plants with either the biostimulant (at 0.5 mL⋅L–1) or VAFs had similar tipburn reduction and shoot fresh mass on 21 and 28 DAT. Without VAFs, increasing the biostimulant concentration from 0 to 0.5 mL⋅L–1 reduced the tipburn rating and the number of tipburn-affected leaves by 96% and 94%, respectively, on 21 DAT and by 75% and 71%, respectively, on 28 DAT. Compared to no VAFs, VAFs eliminated or minimized tipburn throughout, regardless of the biostimulant. Increasing the biostimulant concentration from 0 to 0.25 mL⋅L–1 did not affect shoot fresh mass, whereas increasing it from 0 to 0.5 mL⋅L–1 decreased it by 26% to 32% on 14 and 21 DAT. Compared to no VAFs, VAFs generally did not affect plant growth, except that they decreased shoot fresh mass and total leaf number by 25% and 11% at the biostimulant concentration of 0.5 mL⋅L–1 on 21 DAT. However, neither the biostimulant at any concentration nor VAFs affected shoot fresh mass on 28 DAT. We conclude that the calcium-mobilizing biostimulant is as effective as VAFs at tipburn control of hydroponic lettuce in summer greenhouse environments where VAFs may be undesirable, and that the biostimulant mitigates tipburn without incurring any yield penalty at final harvest.