Climates within which vines are grown vary considerably, so any comments made here have to be tailored to particular situations.
Reports from hotter climates, such as Australia, indicate that the temperature inside a vineshelter can reach as much as 10°C above ambient temperatures, with no adverse effects upon the vines.
High temperatures are helpful in that they kill fungal spores, such as powdery and downy mildew, and some insects, but excessive heat may damage a vine. Vines can sustain temperatures up to approximately 55°C, but their response is dependent upon good soil preparation so that the roots can access sufficient water. Higher temperatures are a component of the vineshelter microclimate that contributes to better growth.
There are some myths about vineshelter temperatures that are important to clarify, particularly if the vinegrower is concerned about limiting temperature levels. Different types of vineshelter will produce different temperature levels.
Facts about temperature and vineshelters:
- Temperature is created from heatload entering from the top of the “tube” and the walls of the tube.
- Temperature is lost through the side walls of the shelter. NOT from the top of the shelter, NOT from the bottom (if ventilated), and NOT through holes in the side walls. Adding ventilation holes to reduce temperature is ineffective.
- The temperature gain and lost through the walls of the shelter is equivalent, such that the variable factor in increasing or decreasing temperature is the open area at the top of the shelter. Therefore, larger diameter tubes will create more heat than smaller diameter tubes (difference could be in range 2 - 4°C).
- Coloured or white shelters are cooler than transparent shelters.
- Humidity levels will not affect the temperature level so waiting for vines to produce leaves before installing the shelter will not have any impact.