Project Blog
Project Blog
Nighttime humidity control is very important for arid and semi-arid greenhouse strawberry production. It is most likely the same for a strawberry production in a heated greenhouse in northern climates. When you hear me say ‘nighttime humidity control’ you may think that I meant ‘reducing humidity to avoid condensation’ which may be a more “normal” practice in greenhouse to eliminate the droplets falling over plants. No, we are not dehumidifying, we are humidifying to reach at around 95% (or greater) for at least three good hours inside the canopy to control tip burn and calyx burn. Plant pathologists think that we are crazy, but relatively dry climate during the day seems to help by keeping plants free from serious fungal disease. This tip burn is associated with calcium deficiency caused by reduced turgor at night by cuticular transpiration or during the day by excessive transpiration from unfolded leaves. Please see our website page on ‘tip burn’ for more information.
During previous years, when our strawberry project was micro-scale, we were manually covering the raised troughs at night with either a floating plastic cover or a curtain hanging from a wire cable above the plants. This year, we installed an under-bench misting system with an on-off timer, so that it would increase the humidity during the night but not wet the plants. We also target the minimum duration reaching the 95% relative humidity to be three hours (see the chart below). This magic number (3 hours) was suggested by a strawberry expert in Belgium and it seems that it works very well. The only issue is that misting tends to wet (just) the excessively low hanging fruit (Portola) and some fruits become infected with gray mold which was not the case at all for other fruits or when we are simply using a curtain system or floating cover even though we probably had a more wet situation when we were covering strawberry plants by curtain or floating cover. The reason is obvious. Water (from well or municipal source) carries more microbial pathogens than water evaporated and condensed from vapor. Another issue is additional use of water which is a precious resource in arid and semiarid agriculture. We will need to find a way to minimize water use.
This project is funded by a grant from the Walmart Foundation and administered by the University of Arkansas System Division of Agriculture Center for Agricultural and Rural Sustainability.
Under-bench misting at night
Monday, October 21, 2013