Leaf Wetness within a Lily Canopy

Rain, fog, drizzle, mist and dew are meteorological phenomena, which cause leaf wetness, i.e. free liquid water on plant leaves. Leaf wetness affects plant growth, plant life, but also offers free water availability for example for plants and small animals in deserts and for fungal spores. Lilies (Lilium spp.) are a very important export product in the Netherlands. If leaf wetness exceeds a critical value along with a certain temperature level, then the fungal disease Botrytis elliptica, or ‘lily fire’, develops rapidly within this crop canopy and causes enormous harm. Botrytis affects the leaves and is visible by showing brown spots. These spots reduce the photosynthesis process that hinders a healthy growth of the lilies and last but not least these ugly spots reduce the salability of these plants. A reliable early warning system for this disease is most welcome for lily growers. A wetness duration experiment has been carried out in a lily field just behind the coastal dunes in the Netherlands. Moreover a within canopy multi-layer model has been applied to simulate the leaf wetness within the canopy in layers with equal leaf area index. This simulation model is an extension of the model of Pedro and Gillespie as suggested earlier in 1982. It appeared that in most cases leaf wetness started in the upper layers of the canopy followed by the middle and bottom layers, respectively. The same happened during the early morning drying process. Somewhat after sunrise the upper layers started to dry followed again by the middle and lower layers, respectively. The longest leaf wetness duration occurred in the lower region of the canopy. The multi-layer model performed well. The calculated leaf wetness duration agreed within 10 min with the result obtained with the leaf wetness sensor.