Southern California – May 26, 2014

This report covers conditions and observations made between Monday, April 28 and Sunday, May 25, 2014. The next report is scheduled for Monday, June 30, 2014. However, in the event of any significant occurrences prior to that date, this site will be updated as soon as possible.

The first of this report’s photos for the southern region present a down-the-row view of a planting in the Porterville area of Tulare County, showing the classic yellowing imparted by the use of high pH irrigation water. Note that the orchard has also received an application of Gypsum, which has been spread along the drip line. Gypsum, which is calcium sulfate, is used to enhance water penetration into the soil and to reduce salt levels. Our second photo shows an orchard in the Firebaugh area of Fresno County with the tell-tale salt rings along the drip hose betraying the use poor quality water, while our final image shows a grower in the Chowchilla area of Madera County eliminating the weed growth within a new orchard in an effort to reduce water consumption.

A graphic depiction of the southern San Joaquin Valley’s daily maximum temperatures during May reveals a sine wave pattern of the ebb and flow of the daily readings. Maximum temperatures peaked three times during the period, first in the low to mid 90’s in the first days of the month, then in upper 90’s to just over 100 degree at mid-month and finally in the lower 90’s in the period’s closing days. Maximum readings in between the cycles of heat reached only into the upper 60’s and lower 70’s. Morning minimum temperatures exhibited a bit more stability, with readings reported predominately in the 40’s and following the cyclic pattern of the daily highs.

Official stations reported trace amounts of rainfall during the period in the northern half of the region as scattered showers roamed through the valley on the 6th and 22nd of May. As with the central region, winds were a factor in the region’s weather on several days during the period with speeds reaching into the upper teens and mid 20’s on the windiest days.

Water dominates the mindset among growers in the southern San Joaquin Valley as they worked balance the finite amount of water available this year with the orchard’s moisture requirements. Windy days and periods of above normal temperatures have exacerbated the situation, driving water consumption by the trees. Measurements of the daily evapo-transpiration rate published by the California Irrigation Management Information System, CIMIS, show typical pan evapo-transpiration, ETp, rates at 0.25 to 0.30 inch per day during the period. However, windy conditions have also driven ETp rates above 0.35 to as high as 0.40 inch. Growers use the ETp rate in a calculation, along with a variable crop factor, known as a crop coefficient to estimate the actual evapo-transpiration of the crop , or Etc, the water used by the trees on each day. For growers facing limited water supplies, University of California researchers are recommending that the amount of water be spread evenly throughout the growing season, while trying to maintain enough for a post-harvest irrigation to support the flower buds needed for the next crop.

Observers are reporting that growers in the Madera County area are facing dropping water levels in their private wells. Well drillers and service companies have been kept very busy trying to keep up with the demand for their services. The U.S. Bureau of Reclamation, which manages the Federal Central Valley Project has announced that it will use water stored behind the Friant Dam near Fresno to supply water to the group of west side irrigation districts, collectively known as the Exchange Contractors. This action leaves lands along the east side of the region without a major supply of water for the season.

With the focus on water, growers’ normal crop management responsibilities must also be met. Observers have reported that populations of web spinning spider mites have increased to levels requiring treatment in many orchards, particularly in the southern areas of the region. As shown in the photos accompanying this report, growers have been applying Gypsum to the orchards in an effort to enhance water penetration and leach salts from the root zones. Weed and insect management operations have also played a large role in grower schedules as they work to support the crop.

At the end of the period, kernels of all varieties are now fully solidified, or nearly so throughout the region. The solidified kernels are able to tolerate a bit more water stress, allowing growers with limited supplies to reduce their irrigation volumes slightly. All in the region will be monitoring their orchards closely for the next major phase of crop development, the hull split of the Nonpareil, which could begin at the end of June.

Current weather at the National Weather Service
Photos: Matt Willson, Mel Machado and Ernie Reichmuth, 5/26/14
Click an image to enlarge it.

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