Many growers of Alstroemeria are familiar with this phenomenon: white dashess in the leaves. What causes them? The Greenhouse Horticulture & Flower Bulbs Business Unit of Wageningen University & Research (WUR) investigated whether they are the result of cold leaves due to radiation losses during clear sky nights. There turned out to be no relationship.
The research hypothesis based on previous observations was that radiation losses could be the cause of leaf dashes in Alstroemeria. Due to radiation, a crop loses heat to the next (colder) surface that is above it during clear sky nights. The more barriers between the crop and the cold sky above it, the lower the radiation. A double screen therefore reduces heat losses by radiation.
WUR and the FloriConsultGroup investigated whether an energy-efficient greenhouse climate with, among others, a double screen, also reduced the incidence of leaves with dashes. To this end, with the help of LetsGrow.com, the climate data of four companies (with five departments) were compared over a period of eighteen months. Growers noted during this period whether leaf dashes occurred. The data and findings were discussed with the growers.
From the comparison, other factors besides crop temperature compared to air temparature seemed to correlate with dashes.. The appearance of the dashes turned out to be more complex and depended on several factors, including RH, CO2, lighting and greenhouse temperature. In an additional test in an air-conditioned greenhouse at WUR, dashes were induced in 2 sensitive varieties at a night concentration of 1800 ppm CO2 in combination with high-intensity lighting and a night temperature of 18° C. At a lower night greenhouse temperature at and at 95-100% RH, the plants did not develop white dashes.
Being able to induce thedamage is a breakthrough in the long search for the causes of the leaf dases, with a surprising role of high RH in protecting the plants from developing dashes. Climate comparison appears to be a powerful tool for growers to develop and share knowledge, as the growers indicated during the last project meeting.
The research took place as part of the 'Monitoring energy innovations in practice' from the program “Greenhouse as source of Energy".