January Pistachios Task List

By Robert Beede, U.C. Farm Advisor, Emeritus

Chilling and Cold Weather Update: We have eased into the cold weather this year, and thus far have not had any really low temps that might hurt the pistachio trees. You can drive around and still see plenty of almond trees with a full head of hair. Thus far, the chill accumulation for this winter appears good statewide. Table 1 provides the chill portions for various sites throughout the Valley between September 1 and December 13 for the past three winters, and 2010, in which over 70 chill portions were accumulated by February 15. This is well in excess of the 58-60 chill portions estimated to satisfy the rest requirement of the Kerman cultivar. The Peters male may have a chill portion requirement as great as 65. The values in parentheses are the total chill portions accumulated by station and year.

As you can see, 2013 and 2014 were significantly warmer than 2010, in which most areas of the state had 70 or more chill portions. The table also shows that December has not been the problem month for chill accumulation during the past two winters, since the values are similar for many stations between 2010 (good chill year) and the past two low chill years as of mid-December. The table also shows that the Arvin/Edison and Coalinga stations might be used as the “canary in the coal mine” for early assessment of low chill issues. HOWEVER, now that all of you have your OWN weather stations at your ranch, you can obtain much more valuable data than a poorly maintained CIMIS station being used as a scratching pole by a white-faced steer! That statement, along with all of you filling out your Good Agricultural Practices worksheets and winter sanitizing, will be realized when Santa brings me an original Ferrari 250 GTO!

Table 1. Chill portion accumulation for various CIMIS stations statewide from 9/1-12/13 for selected years.
Numbers in parentheses are the total chill portions accumulated at each station by year from 9/1- 2/15.

Year 2015 2014 2013 2010
Durham 25 22 (55) 20 (54) 28 (70)
Patterson 20 23 (63) 22 (63) 26 (73)
Madera II 25 25 (52) 15 (57) 23 (NA)
Parlier 26 27 (64) 22 (53) 27 (74)
Five Points 24 15 (52) 20 (55) 24 (69)
Coalinga 25 13 (48) 20 (53) 28 (70)
Shafter 24 25 (61) 24 (63) 23 (70)
Delano 25 16 (58) 22 (56) 24 (73)
Blackwell’s Corner 24 15 (52) 21 (50) 27 (75)
Arvin/Edison 23 10 (44) 21 (55) 22 (66)
Porterville 30 20 (63) 22 (59) 27 (63)



For those of you still asking your ranch manager what happened to the 2015 crop, it was definitely the lack of effective chill hours. I have gone back and reviewed the observations of Dr. Julian Crane, as well as the research that Dr. Louise Ferguson and I performed individually and collectively, and it all clearly states that Kerman and Peters do not grow normally when they do not receive adequate winter rest. Our research efforts suggest Kerman requires 750 hours below 450 F, and Peters 850 hours in order to leaf out and bloom promptly in the spring. One experiment suggested that Peters continued to benefit from cold temperatures up to 1200 hours below 450F. It was also reported in these studies that a minimum of 500 hours below 450 F was needed to initiate much bud break from Peters. University of California Circular 179, “Deciduous Orchards in California Winters,” by W.H. Chandler and D.S. Brown (1936), states that December and January are the two most critical months in California to satisfy the rest requirement. During the past two winters, the unusually warm temperatures in January have not provided its complement of chill hours.

The effect of high winter temperatures is thought to be two-fold: They negate the effect of chill hours already accumulated by altering the complex physiological processes occurring during dormancy, and they elevate the bud respiration rate which consumes the limited amount of carbohydrates critical for spring growth. UC Davis Plant Sciences Associate Professor Maciej Zwieniecki (Dr. Z) has joined our pistachio industry research team to study this important aspect of tree biology. Dr. Z suggests there may be a critical amount of carbohydrates and other growth substances needed to produce normal growth in the spring.

This may explain why oiled trees performed so poorly this past season. Oil is thought to enhance rest breaking by causing a slight stress to the tree that is not phytotoxic. In the process of metabolizing the oil, the tree increases its respiration rate, which renders it more responsive to favorable spring temperatures for growth. Thus, the high January temperatures and oil treatment possibly had a compounded effect on carbohydrate depletion from elevated respiration. When it came time for bud break, the deficiencies in both chilling and available food created the perfect storm for poor leaf out and fruit set. There could have also been detrimental effects to male and female flower development and receptivity. The pistachio industry has plans to study flower development this winter and spring. Also, because of the uncertainty of this winter’s weather pattern, oil application is not being suggested at this time due to the negative impact it had on yield last season.

To check on your local chilling, go to the “Weather-Related Models and Services” section of the UC Fruits and Nuts Center. Select “chilling accumulation models” from the menu, and then “Cumulative Chilling Portions.” This site allows you to see the chill portion accumulation for every CIMIS station in the state. You can also click on a given station to get historical data. I find this helpful in estimating where we are relative to other years. You can also compare chill portions to chill hours at this webpage.

Keep in mind that these stations were designed to accurately estimate water use, NOT chill accumulation. The data is collected in an open grass-covered area that may influence the temperatures compared to those within the orchard environment. The absence of fog also causes temperature differences up to 200F between ambient (air) and the buds. Obviously, we are concerned with the bud temperatures, so it would be helpful to make note of those warm, fog-less winter days. Monitoring actual bud temperatures with tiny thermocouples is underway this winter, and the results will be shared when available.

Tests of clay or calcium carbonate-based materials intended to either reflect solar radiation or diffuse it are also planned for this winter. Results, last season, from David Doll, UCCE Farm Advisor, Merced County, and Rob Goff, Wonderful Farms, showed a 200- to 250-pound increase in CPC yield over untreated trees. In David’s trial, the untreated trees produced almost no crop, compared to 720 pounds in Rob’s Kern County trial.

So, the data thus far suggests that spraying these materials to mitigate the negative effects of warm winter temperature does not assure you of a normal crop, but it might prevent NO crop! As of mid-December, there has been no need for application, due to the absence of warm days. Applications are planned for the beginning of the New Year, and the use rates of the various products vary from 30 to 50 pounds per acre. Re-application is recommended after significant rainfall. Applications are not presently advised in February, unless one desires to delay bud break and bloom due to the risk of spring frost in your growing area. The cost per application is estimated at $80-90 per acre. Those interested in more detail can read David’s report at: http://thealmonddoctor.com/2015/10/26/kaolin-clay-may-be-useful-in-incre....

Rain? Bring It ON! Growers wishing to periodically check on reservoir and snowpack status can do so my website: http://cekings.ucanr.edu/Agriculture/Grapes_Tree_Fruits_Nut_Crops/. Select “Management” in the main menu, then “Water and Weather.” Select “Snowpack Status” from the menu, which will link you to the state water resources webpage. This page converts snowpack into water content and plots it for three major sections of the state. It also compares this year to wet and dry seasons and the 30-year average. These plots really provide a visual picture of where we stand in water availability.

Thus far, the plot for this year is encouraging, but much more is needed! Selecting “Reservoirs Status” from my webpage menu can access statewide reservoir conditions. This takes you to a DWR website that lets you click on the reservoir of interest. It then brings up information about current and historic water status and allows you to select what years you would like to compare in graphic form. It is pretty neat, and gives you lots of sound data to spread around at the coffee shop! Keep rain in your prayers!

Navel Orangeworm Management: I wish I could pass on this subject, since we are all so tired of hearing about it, but your processor will tell you that CLEAN CROP is the KEY to keeping your markets! If we are going to rave about California pistachios, we had better walk the talk, or get ready to figure out what to do with the carryover! Brag Higbee, Wonderful Farms Entomologist, can now tell you that over time, SANITATION PAYS in pistachios! So unless you know something I do not, clean up your orchard or lose big money in premiums and lost markets. I need not tell you how important the overseas markets are these days! They want nice clean, stain-free product, just like in the California Pistachio ads!

Happy New Year, Farming, and see you at Pistachio Day, Wednesday, January 20, 2016, at the Visalia Convention Center!