Welcome to our Ag Blog. Our field scouts will offer a unique ground-level perspective from the field to you as an independent field scout with the San Joaquin Sustainable Farming Project. Our mission is to promote sustainable farming systems throughout the Central Valley and provide you with the latest information about cotton, almond and alfalfa crops. From time to time, you'll also find guest posts from our project team and other contributors. This Blog is produced by Gilbert Mohtes-Chan.
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
“FREEZE WARNING REMAINS IN EFFECT FROM 2 AM TO 8 AM
SATURDAY... Sub-freezing temperatures are imminent or highly likely. These conditions will kill crops and other sensitive vegetation.”
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.
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
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.
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.”