Working for Permanent Protection of Agriculture and its Resources
Best Practices for Frost Control
- Keep cover crops and other vegetation closely mowed to the ground. Moderate or tall vegetation lowers vineyard temperatures at night and increases frost risk.
- Double-pruning or late pruning will retard budbreak. Conduct the final pruning after the more apical buds have pushed.
- Apply copper to reduce ice-nucleating bacteria.
- Use your own thermometer. Frost is very site-specific, so don't rely on a remote weather station or your neighbor's thermometer. Measure well away from your neighbor's vineyard if it has sprinklers in operation.
- Better yet, use a bulb-type, aspirated psychrometer (wet and dry bulbs). The west bulb is very useful. Portable electronic types are available, but are less accurate at low dew points than are bulb types. Sling psychrometers may also be used.
- Use dew point values to determine your threshold for sprinkler start-up. Use a psychrometer and associated look-up tables, if possible. If not, using publicly available dew point information within your region is better than using nothing.
Guidelines: Dew point greater than 35F, little chance of frost damage; dew point of 24F or higher, turn on sprinklers at 34F air temp; dew point between 20 and 23F, turn on sprinklers at 35F air temp; dew point of 19F or lower, turn on sprinklers at 36F air temp. These apply only when frost is predicted. Turn off sprinklers when air temperatures rise back to 34F, ice is melted or wet bulb temperature exceeds 32F.
- If using a Wet-bulb device, frost control must be active for wet bulb temperatures of 32F or lower.
- Wet soil surfaces conduct and store heat better than dry ones. If soil dries out by late spring and frost is forecast, brief irrigations (1-2 gallons per vine) periodically may help.
- Use wind machines to assist in frost control, where available and applicable.
Source: Ag Alert, April 2009
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