Tipburn of hydroponic lettuce
Inner leaf tipburn is a common disorder inhydroponic lettuce during the summertime. Symptoms include brown (necrotic)spots on the tips and edges of young leaves developing in the center of a headof lettuce. The young leaves can become distorted and ultimately the headbecomes unmarketable.
Inner leaf tipburn develops due to poor calciumsupply to young developing leaves. Most often the symptoms are not due to lackof calcium in the root-zone but rather environmental causes leading to poorcalcium supply to young leaves. In the summertime, high light levels can causethe plants to grow too fast and the roots cannot take up enough calcium to keepup with new growth. Warm temperatures and high humidity can also exacerbate thesymptoms by promoting rapid growth and poor plant transpiration.
Once symptoms have become apparent, there is notreatment which can reverse the symptoms. Therefore management of inner leaftipburn of lettuce relies on prevention. Rarely, is the disorder caused by lackof calcium in the root-zone. However, it is prudent to ensure that yournutrient solution contains sufficient calcium either from your water source oradded fertilizer.
Assuming sufficient calcium is supplied in thefertilizer solution; the primary tools for preventing inner leaf tip burn are promoting environmental conditions thatfavor plant transpiration as well as avoiding excessive daily light integrals(DLI). Low humidity and good airmovement (especially using vertical airflow fans) will promote planttranspiration which will promote supply of adequate calcium to the shoot tip. Tipburncan be a particular problem in summer greenhouse conditions because when thereare naturally high DLIs. Therefore, greenhouse shading is a must when growinghydroponic lettuce in the summer. Retractable shade curtains are useful as shadecan be deployed when needed, but allow natural light through on cloudy days.Depending on the cultivar and your airflow conditions you may need to limit DLIto 12 to 17 mol·m-2·day-1.
For more information on inner leaf tipburn oflettuce see e-Gro Alert Vol 4.32.
Neil MattsonAssociate professor and greenhouse extension specialist, Cornell University
Neil Mattson is an Associate Professor and Greenhouse Extension Specialist at Cornell University. He has an appointment in research, extension, and teaching. He researchers strategies to optimize floriculture and vegetable crop production while reducing energy, fertilizer, and water resources. He directs Cornell’s Controlled Environment Agriculture group which develops lighting and greenhouse control strategies to maximize hydroponic vegetable production.