January 2017 - Pistachio Task List

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

Chilling and Cold Weather Update: Those of you who are outside every day know that it has been pretty warm. The only cold weather occurred during the first week of December in which many locations within the Central Valley experienced three to five days of temperatures ranging from 30-320°F. The Colusa CIMIS station reported 260°F the morning of December 6. Table 1 provides the chill portions for various sites throughout the Valley between September 1 and December 13 for the past four winters, as well as 2010 in which over 70 chill portions were accumulated by February 15. This exceeds 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 dormancy was well satisfied throughout all areas of the state. The 2015 data shows good chill accumulation was well on its way throughout the Central Valley in mid-December, and continued cold temperatures through January contributed to the record 2016 crop. In contrast, 2014 was already showing deficient chill accumulation at several locations by mid December. The Arvin/Edison and Coalinga stations might be considered the “canary in the coal mine” for early assessment of future low chill winters. 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! The importance of orchard-accurate chill data is realized by the 2016 CIMIS data I have summarized for your consideration. As you can plainly see, chill portion accumulation is not good thus far, and in some locations, less than the 2014 winter.

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 2016 2015 2014 2013 2010
Durham 21 25 (66) 22 (55) 20 (54) 28 (70)
Patterson 16 20 (59) 23 (63) 22 (63) 26 (73)
Madera II 22 25 (66) 25 (52) 15 (57) 23 (NA)
Parlier 14 26 (67) 27 (64) 22 (53) 27 (74)
Five Points 15 24 (65) 15 (52) 20 (55) 24 (69)
Coalinga 16 25 (62) 13 (48) 20 (53) 28 (70)
Shafter 12 24 (59) 25 (61) 24 (63) 23 (70)
Delano 15 25 (65) 16 (58) 22 (56) 24 (73)
Blackwell’s 18 24 (67) 15 (52) 21 (50) 27 (75)
Arvin/Edison 15 23 (61) 10 (44) 21 (55) 22 (66)
Porterville 14 30 (76) 20 (63) 22 (59) 27 (63)


I have gone back and reviewed the observations of Dr. Julian Crane, as well as the research 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 450°F. 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 2013 and 2014 winters, the unusually warm temperatures in January did not provide 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 in 2015. Oil is thought to enhance rest breaking by causing a slight stress to the tree which 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 sugars 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. Because of the current uncertainty of this winter’s weather pattern, oil application is NOT being suggested at this time due to the negative impact it had on the 2015 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 which may influence the temperatures compared to those within the orchard environment. The absence of fog also causes temperature differences up to 200°F 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.


Clays and Calcium for Dormancy Improvement? Tests of winter applied kaolin clay or calcium carbonate-based materials intended to either reflect solar radiation or diffuse it continue. Results from David Doll, UCCE Farm Advisor, Merced County, and Valley Orchard Management, showed a 200 to 250 pound increase in CPC yield over untreated trees when kaolin-clay was applied prior to the 2015 season. The data thus far suggests that spraying these materials to mitigate the negative effects of warm winter temperatures does not assure you of a normal crop, but it might prevent NO crop!

This past winter, Carl Fanucchi and I collaborated with Tim and George Baker, researcher and owner, respectively, of ORCAL, the company which manufactures ultra-fine, dry ground calcium carbonate, which is marketed in liquid form as Mask® and Diffusion®. We performed UNREPLICATED screening trials in two locations; one in Buttonwillow, and the second east of Highway 99 on Pond Road. The screening trials included single and double applications applied January 12 and February 12. A December treatment was planned, but the field could not be accessed. Flower bud temperatures were monitored in treated and untreated areas using tiny thermocouples inserted into the buds without causing their death. The resulting data showed bud temperatures were reduced by as much as 100°F, and the rate of heating during the morning hours was also slower. Calculations indicate that the January treatment increased chill portion accumulation by about 13%, due to the lower bud temperatures. Weekly rating of the treatments for bud break and bloom were also performed. The treated trees emerged more evenly, and the second treatment of Diffusion applied in February delayed development by four to five days. The single January treatment developed at about the same rate as the untreated. These observations are from a site in which the rest requirement for pistachio was satisfied during the 2015 winter. The results may differ when the chill portions are insufficient. Carl successfully tracked yield from the treated and untreated trees at both sites with the outstanding cooperation of the growers. A yield improvement was observed in the Diffusion treated plots. The increase was more than sufficient to pay for two treatments. However, we are not reporting the actual yield increase, because these trials were NOT replicated, hence the data is considered observational only.

Calcium carbonate works differently than kaolin-based clay materials. Kaolin clays reflect light to reduce the absorption of solar radiation by plant tissue such as flower buds. It is also marketed as a finely ground powder, which growers report to be more difficult to apply than liquids. In contrast, calcium carbonate crystals modify the incoming light through a process called double refraction. This essentially divides the light rays as they intercept the crystals, and thus reduces their energy. Incoming light can also hit the crystals whose size matches the incoming wavelength, resulting in a so-called “sparkler effect” in which light is dispersed in multiple directions. Both light division and the sparkler effect reduce energy absorption by the plant, resulting in lower temperature. My intent in describing the methodology of calcium carbonate is NOT to suggest it is better than kaolin-clay. It is simply to inform the reader that kaolin-clay and calcium carbonate are distinctively different in their mode of action.

As of mid-December, this winter is as much as 40% lower in chill portion accumulation. This task list seeks to alert you to this fact, so that YOU can decide if any action is warranted to try and mitigate the current warm winter trend. We cannot tell you if kaolin-clay or calcium carbonate provides statistical improvement in chill accumulation and subsequent yield benefit, because this research is slow to progress, due to the complexity of its performance. The weather cannot be controlled to secure the needed temperature differences.

Field reports indicate some growers have begun treatment of these products in early December as a precaution. The use rates of the various kaolin-clay products vary from 30 to 50 pounds per acre. The liquid calcium carbonate is typically applied at four gallons 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.

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! Statewide reservoir conditions can be accessed by selecting “Reservoirs Status” from my webpage menu. This takes you to a DWR web site 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, January18, 2017, at the Visalia Convention Center!