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Ask Your PCA: What do orchardists need to do to be proactive this spring because of the temperatures dropping to below freezing?

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Issue Date: March 15, 2006
Mike Marshall, Sutter County PCA

With the current low nightly temperatures, we have already seen frost damage in almonds and peaches. The extent of this damage is still unclear as symptoms do not appear right away.

The almonds appear to be affected to a greater degree than the peaches, which are just now beginning to bloom. At this point we have not seen damage in the prunes, which are still fairly dormant.

Young walnut trees are a concern as their tender wood can be susceptible to below freezing temperatures although these very low temperatures have not been observed thus far. Olives are showing some burn on the leaves but the crop should not be affected at this time. We have sustained freezing temperatures for the last several nights and expect this to continue for the next few days. As time progresses these orchard crops become more susceptible to freezing temperatures.

Many growers have prepared for potential frost by managing their cover crop either with mowers or herbicides. Firm, bare, moist soil can promote higher nightly temperatures in the orchard environment. Growers who have sprinklers or micro sprinklers are irrigating at night beginning several degrees before freezing temperatures occur and ending after the orchard temperatures are several above freezing. The irrigation water, which is above freezing, adds heat to the orchard and can offer some frost protection. Drip irrigation is thought to add little protection against frost, but some growers with this system still choose to irrigate as a final preventative measure and we have seen some benefit this season.

Other growers are running water during the day to darken the soil surface and absorb more of the sun's energy to be released at night. Larger growers have successfully employed helicopters, pushing warmer air from the inversion layer above to mix with the cooler air on the floor, raising the overall temperature in the orchard.

With the upcoming wet weather there is a great potential for spring diseases. We will be targeting these specific weather events with fungicide applications.

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.

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