AVA Climate Challenges

I have always been concerned about high winter temperatures in Temecula. Historically, February has been a warmer month in Temecula than March. So far, so good; however, last winter we saw January temperatures over 90 degrees. I would be concerned about very early bud break followed by low temperatures, including frost. It may become necessary to delay pruning in frost prone areas until early spring.

I’m not sure what the concerns on soil pH might be. However, using lower amounts of chemical sourced nitrogen fertilizers is a good idea. With the notable exception of Calcium nitrate, those fertilizers lower soil pH over time. Eventually, the pH can move into a range below 5.5, where nutrients begin to become less available to plants.

Growers should also keep an eye on soil salinity. Electrical conductivity (EC) levels above 2.0 (measured as dS/m or mmho/cm) progressively show increasing resistance to water uptake by plants. There is a direct relationship to crop loss as salinity levels increase above 2.0.

Use of organic fertilizer and amendment products are a good way to avoid or mitigate salinity. However, some years back, there was a big problem in Temecula vineyards caused by widespread use of composted mulch that itself had excess salinity. The effects where the opposite of what would be expected from applying mulch under the vines, which became highly stressed and leaf burned.

Organic sources help build soil health, which mitigates heat stress. Also beware of the amount of Nitrogen traditionally recommended. (You don’t want excessive growth. Remember?) Historically recommended Nitrogen amounts reflect vineyard conditions in the Central Valley where vineyards product 12 to 16 tons per acre. That is not our goal, even if we could do it!

Hopefully it never comes down to this, but there has been an extensive research project in Australia testing how little water can be used in a bad dry year. The idea was not to produce a crop, but see how low irrigation could go to let the vineyard survive that year, but still produce a good crop the following year when the water crisis ended. They tested different varieties and rootstocks/own-rooted vines. I’m not recommending this, but the information exists, if needed.

by Peter Poole
Expert Viticulturalist

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