Upper leaf necrosis or ‘leaf scortch’ in Oriental hybrid lilies is a calcium deficiency disorder that develops early in the crop life-cycle. It is a difficult problem to treat because the obvious visible symtoms (brown upper leaves) develop as many as 25 days after the actual injury to the leaf cells. The symptoms are curled, distorted or dead upper leaves at or near the flowerbuds. The symptoms first appear on young expanding upper leaves about 30-35 days after planting when plants are 30-35cm tall. Symptoms commonly start on the leaf margins and are therefore difficult to detect at an early stage. On a severely infected leaf, watery tissue appears on the leaves which then turns brown several days later. Only a small quantity of calcium is contained in the bulbs and as they grow the developing roots will start to absorb calcium from the substrate. The deficiency disease develops where, for one reason or another, transpiration is inhibited thereby reducing the amount of calcium translocated from the roots to the leaves. Leaf scortch will take place in sitiuations of high growth rate where the available calcium is insufficient to support that growth rate. Some leaves might be shaded by others (especially where there is a more enclosed shoot apex grown from larger bulbs). The same effect occurs by shading the crop or providing excessive relative humidity, thereby reducing the air movement and transpitaion. The disorder rarely shows itseld when largher bulb sizes are used. Avoiding overhead irrigation, providing adequate ventilation and artificial lighting in the winter will help overcome the problem. Frequent application of foliar sprays from the period of 30 to 43 days containing calcium (0.6% Calcium Nitrate or 0.45 for Calcium Chloride with surfactant) can also be effective. The spray is directed at the young enclosed leaves. Leaf Scorch is also cultivar dependent, some being more susceptible that others (Star Gazer, Acapulco and Muscadet are especially susceptible). Yao-Chien Chang, William B. Miller, “GrowerTalks” April 2004 www.growertalks.com |
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