Monday, February 26, 2018

Deep Freeze Means There’s No Time for Growers to Chill Out during the Night



 Weather Watchers issued the chilling news to growers: 

“FREEZE WARNING REMAINS IN EFFECT FROM 2 AM TO 8 AM PST
SATURDAY... Sub-freezing temperatures are imminent or highly likely. These conditions will kill crops and other sensitive vegetation.”

That’s what the U.S. National Weather put out over the weekend for the Valley. The low temperatures were dipping down to the mid-20s. Worst yet, forecasters were warning everyone the freezing temperatures would last as long as six hours.

“Long durations of below freezing temperatures will kill unprotected vegetation. Agricultural interests should closely monitor minimum temperature forecasts and make preparations to protect frost and freeze sensitive vegetation,” the Weather Service goes on to add.

It certainly wasn’t the best way to wrap up a week that endured several days of freezing temps last week. Suddenly, this rain-starved winter became even tougher for growers who are forced to spend the bone-chilling nights rushing to protect their valuable crops. 

Almond growers have been out irrigating their crop to raise the temperature, trying to build up humidity to slow the drop in temperature. They fear the subfreezing temperatures will damage the buds during this critical bloom period. It may be a few weeks before growers see if there is an increase in buds dropping off the trees.

It’s not just the overnight frost growers are worried about. The cool daytime temperatures could slow the pollination process. Bees work best when the weather is at least 55 degrees
.
Our long-time collaborator, David Doll, a Merced County UC Cooperative Extension pomology farm advisor specializing in almonds, has offered freeze warning protection tips on his online Almond Doctor column.

“The point to turn on irrigation is dependent on dew temperature and the expected low temperature. Starting the irrigation too late when the dew temperature is low can increase the risk of damage. Turning off too early can also increase the risk of damage. Techniques utilized to determine when to start and turn off irrigation usually revolve around the use of a ‘wet bulb,’ ” he wrote in his February 17 column.

Irrigating an orchard to protect against the freeze.
He goes on to say: “Irrigation application rates need to be high enough to provide an increase in air temperature. Application rates should exceed 30 gallons per minute per acre. Rates less than 15 gallons per minute per acre may lead to freezing of irrigation lines/spaghetti tubing. The critical temperature of damage will vary by bloom stage and variety. At full bloom, temperatures at or below 27-28F can cause crop loss. As trees leaf out and nuts begin to develop, the sensitivity to cold temperature increases.”

Finally, he adds: “in flood and drip-irrigated orchards it may not be possible to have high enough discharge to have a warming effect of the water, but adding moisture to the soil can increase the warmth of the field – which is why mowing any vegetation is advised within these systems. Mowing may not be as critical in orchards that are able to apply irrigation water over the top of a cover-crop.”
Go to his Almond Doctor website to learn more about frost protection methods for almonds.

Let’s hope March brings warmer temperatures and some much-needed rain.













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