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04/01/2008 02:00:00 AM

Table 2 shows the benefits of a bare, firm moist soil in contrast to the least affective frost conditions.

Table 2. Comparisons between optimal soil conditions for frost.

Soil Characteristics Vegetation Temperature benefit
Bare, firm, moist None Warmest Optimal
Moist Shredded cover crop 0.5 ˚F
Moist Low growing cover crop 1-3 ˚F colder
Dry, firm Freshly disked 2 ˚F colder
Dry to moist High cover crop 2 ˚F colder Least optimal

Soils that have been recently cultivated or disked need to be irrigated soon after the soil has been disturbed. Cultivated soils do not retain heat well because they are dry and have numerous air pockets. Native vegetation or cover crops that insulate soils from absorbing heat should be mowed or disked and followed by irrigation or significant precipitation.

Irrigating during a frost event can be beneficial. On nights that low temperatures are expected pumps should be turned on early enough that the entire vineyard is covered. Depending on size it may only be feasible to irrigate the most susceptible areas (low lying) where cold air tends to drain. Doing so will improve the chances of protection.

Vineyards that are drip irrigated should not have their row middles cultivated. Drip irrigation should be turned on to wet as much soil as possible. Growers will have to be especially vigilant to the weather forecast in order to start irrigating well in advance of the frost event. Cover crops or native vegetation should be mowed prior to budbreak and often as is necessary after the vines awaken. Row middles should not be cultivated unless a significant rain event has been predicted. Doing so could result in significant losses if frost should appear. It only takes a single frost event (one night at freezing or below) to experience a complete loss.

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