May 2015 Orchard Task List for Pistachios

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

Field Oil Observations: With the help of my good buddy, Carl Fanucchi, I have continued rating trees treated with and without oil in Buttonwillow and Tejon, as well as observing trees in Kettleman City, on the west side up to Firebaugh, and on the east side of Madera. I have also fielded many calls from growers unhappy about the lack of uniformity from oil treatment, and whether or not flower-bud drop was related to the oil. I wish I had answers to all the conditions I have seen in the field. About the only thing I know for sure is that in the 10 years that I studied oil application and its rest-breaking effects, I never saw all of the problems that I have seen in the past two years. This, of course, begs the question, why?

One factor that has certainly changed is the winter weather patterns. During most of my replicated trial work (1997-2002), there was either adequate rest, or in the years of insufficient chilling, the fluctuation in winter temperatures was not nearly as great as it has been recently. I consider this a highly significant factor because common horticultural sense and limited research suggests it is the bud temperature that is of greatest concern, not the ambient temperature. In the past, we never emphasized this, because fog prevented the buds from being hotter than the air, due to interception of solar radiation. Although we had some fog this past winter, it was nothing close to the 14-day periods of perpetual whiteness that defined a San Joaquin Valley winter.

Now, I know most of you readers are saying, “Tell me something I don’t know, Beede,” but this single component of pistachio-rest satisfaction is most likely the reason so many of you elected to apply oil with the hope of mitigating the effects of insufficient chill accumulation. Research by Dr. Bruce Lampinen, in walnuts, indicates bud temperatures can be 15-200F greater on a fogless 700F day.

In addition to negating chill hours below 450F, I wonder how these large fluctuations affect the final stages of flower-bud differentiation. Are the female flowers as fertile? Is the viability of the male pollen less? If answers to these questions exist, I must have been in the restroom when they were provided. We know that their time of emergence is affected, but I am not familiar with any nut crop data addressing the effect of insufficient chilling on inflorescence quality.

Recent research, using magnetic resonance, showed pear flower-bud differentiation to be affected by both winter water status, and delayed satisfaction of rest. Consecutive years of mild chilling were also shown to have cumulative negative effects on flower development. Is it not known if these results apply to pistachios.

Accurate assessment of the quality of chilling is also another significant factor in evaluating this season’s leaf out and bloom. Due to the lack of fog and large fluctuation in temperatures, we have discounted the accuracy of our traditional “below 450F” chill accumulation method in favor of the chill-portion model. However, this year suggests that the chill-portion model may have overestimated rest satisfaction, since there were growers, with temperature recorders onsite, who accumulated 56 or so chill portions but still experienced markedly delayed leaf out and bloom (14 days behind) of Kerman and Peters. There are now informal discussions about employing the Utah model, which uses a sliding scale that adds or subtracts chill hours based upon temperature. This is in contrast with the chill-oortion model, which does not allow loss of a chill portion due to the occurrence of hot weather after its completion.

Regardless of how chilling is numerically estimated, the best method for assessing rest satisfaction is to observe the tree’s leaf out and bloom pattern. Fortunately, several growers,who oiled left, rows untreated. In general, the oiled trees leafed out and bloomed 14-21 days ahead of the non-oiled trees, depending on the location and degree of rest satisfaction. Carl and I rated the following locations on April 8. Here is a summary of what we found:

Table 1. Description of pistachio ranches rated for leaf out and bloom on April 8, 2015

Location Planting Date Variety/Rootstock Date Oiled Chill Hours < 45°F
1.Vista at Sebastian Rd End 1970 Kerman/Atlantica 1/27/15 420
2.Tejon Ranch 1999 Kerman/ PGI/Atl. 1/26/15 420
3. I-5 and 7th Standard Rd 2009 Kerman/ PGI 1/20/15 800
4. I-5 and Buttonwillow Rd 2005 Kerman/ PGI 1/10/15 800
5. Laval Rd east of 99 1991 Kerman/ PGI 2/5/15 439

Table 2. Leaf out ratings of pistachios with and without 470 oil treatment by ranch. April 8, 2015.

Kerman Female Trees Peters Male Trees
Vegetative Growth % Vegetative Growth %
Location No. 1 2 3 4 5 Location No. 1 2 3 4 5
Green tip 30 15 10 Green Tip 20 30 20
Early leaf out 10 20 40 10 5 Early leaf out 15 40 40 50 10
Leaf out 60 80 45 80 95 Leaf out 65 60 30 30 90
Green tip 85 55 20 Green tip 65 88 20 15
Early leaf out 10 30 30 50 Early leaf out 30 10 70 60
Leaf out 5 15 50 50 Leaf out 5 2 10 25

Note: The oiled trees at location 2 were on PGI, and the non-oiled were P. atlantica.

Table 3. Bloom ratings of pistachios with and without 470 oil treatment by ranch. April 8, 2015.

Kerman Female Trees Peters Male Trees
Floral Development % Floral Development %
Location No. 1 2 3 4 5 Location No. 1 2 3 4 5
Tigh 40 Tight 0
Bud swell 30 10 20 Bud swell 20 20
Pre-bloom 0 10 20 Pre-bloom 10 25 40 15 5
Bloom 0 10 20 Bloom 20 10 10 15 10
Post-bloom 1 30 20 Post-bloom 50 65 30 70 85
BBs 5 20 25 5 20
Nutlets 25 80 15 15 80
Bud swell 76 10 20 20 Bud swell 50 40
Pre-bloom 20 10 20 20 Pre-bloom 40 30 25 10
Bloom 2 60 30 40 Bloom 10 20 35 30
Post-bloom 2 20 30 20 Post-bloom 1 10 40 60

Leaf out and bloom was pretty uniform between trees in the rated orchards. Oil was much less effective on the
45-year-old Kerman on Atlantica orchard at the end of Sebastian Road, but the trees were 25 feet tall with lots of gnarly bark to cover. In addition to only 420 hours of chilling, trees this size would most likely need at least eight to ten gallons of oil per acre applied at 250-300 gallons to get the type of coverage needed for uniform oil response. Even with 5 gallons applied in 150 gallons of water, they were 14 days ahead of the non-oiled section.

I have also visited a lot of orchards where the oil response is very erratic down and across the tree rows. In some cases, there are four rows that look like they did not receive treatment, in contrast to the neighboring rows that do. Walking down individual rows, one can find a wide range in leafing and bloom development. A few orchards also show an occasional one-year-old shoot in the upper canopy that has died back. However, there is no sign of leaf phytotoxicity anywhere in the canopy. Is this “oil burn” or small shoots whose carbohydrate content was so low over the winter that it was all consumed in respiration during the warm days? I do not know.

In one eleven-year-old Westside orchard, there was an abundance of flower buds falling from the oiled trees, and the six rows of non-oiled trees showed little flower-bud drop. If the non-oiled trees set the very late bloom with what little Peters pollen remained, they would clearly have much more crop than the oiled trees. The orchard was very erratic in leafing, and end trees showed signs of heavy oil application. Groups of rows appeared to not have been treated. The orchard was custom sprayed by a very reputable and conscientious applicator.

During the period I researched oil, I honestly never had any of these problems at any of the multiple trials I performed on both the east and west sides of the valley. I ran one trial at Nichols Farms for six years, treating annually with six gallons of Volck 476 oil, in an effort to discover any detrimental effect of long-term oil usage. We saw none, and annual oil treatment aided in slightly reducing alternate bearing. We also performed timed searches for flower-bud drop during the 2002 season. Replicated, three-minute surveys of oiled and non-oiled trees showed greater flower-bud drop on the NON-OILED trees (5.1 versus 8.2). Counts performed in another orchard, in which Volck and 415 oils were applied in both mid-January and February, showed only seven flower buds lost in the mid-February treatment timing compared to 17 for the January timing. However, this level of flower bud loss is insignificant compared to the number present in an on-year.

So, what is one to make of all this? How much of the erratic oil response reported in too many orchards to ignore is attributable to extremely poor winter chilling? Based upon how the non-oiled trees are performing, I would have to say that it is a combination of the oil treatment and the condition of the trees at the time of application. Although the non-oiled trees are 7-14 days behind their normal leafing date (April 1), they are emerging pretty uniformly, and in fair synchrony with the Peters male. In some areas of pistachio production, this might have been the year to pass on oil treatment and accept what Mother Nature gave you. I have stated many times in my task lists that oil treatment presents a risk, and that it is one I would take only in years where I clearly do not have enough winter chilling. Having your own temperature recorder helps greatly in making this difficult decision. It is also clear that we need to refine our ability to accurately estimate effective chilling.

In addition to chilling hours and tree condition, there are also the factors of how horticultural oil is manufactured, mixed, handled, and applied. Much of this is outside the grower’s control, but if you had a negative experience with oil treatment this season, it would seem wise to review all aspects of the oil delivery and application process. This includes how the oil is mixed and maintained in suspension prior to and during sprayer application. If you take time to read up on horticultural mineral oil, you will find that it is a far more complicated material than one would initially believe.

There are also many horticultural questions raised with oil that need investigation. Certainly one is the actual mode of action of oil. If we really understood what it was doing to the plant, then many of the observations made this season might have answers.

Nutrition: May is a good time for nitrogen fertilization. The efficiency of nitrogen uptake from the soil during early leaf out is essentially zero, because nitrogen uptake occurs simultaneously with water use. Consequently, applications made when the tree lacks about 50 percent foliage are subject to leaching beyond the main root zone at three to four feet, especially in production areas averaging 15 or more inches of rainfall. Drs. Rich Rosecrance, Steve Weinbaum and Patrick Brown, UC Davis (Rich is now at Chico), showed that pistachios beginning the off-year were lower in stored N than on-year trees, but uptake occurred primarily between mid-May to late August. As I have said over and over, the “Grand Period of Growth” from bud break to leaf out is all driven by RESERVES stored within the tree, NOT what it is taking up from the soil! Nitrogen applications in March are therefore very subject to loss past the root zone, depending upon rainfall or irrigation amount, and soil type. Obviously, sandy soil textures are less capable of retaining applied nutrients than heavier textured soils. Nitrogen uptake efficiency might reach 80 percent with multiple applications at low rates under drip or low volume compared to “slug” treatments. However, as much as 50 percent of the N applied by water run can be lost from volatilization and leaching past the root zone. Save your rotten tomatoes to throw at me, but I think water run nitrogen is old school, in tree crops. You will find this out when the State starts tracking nitrogen purchases and regulating the amount used.

Rosecrance, and Weinbaum calculated the total N requirement for on-year trees was about 175 pounds. This “calculation” was not simply an entertaining exercise performed on the back of a cocktail napkin at Shorty’s Biker Bar. It was the product of multiple years research in which isotopically labeled nitrogen was applied in measured amounts to the soil around individual trees prior to both on- and off-bearing years, and then the ENTIRE tree was dug out of the ground, cut into specific sections, weighed, chipped, dried, and analyzed for labeled N content. Knowing the amount applied to the soil allowed them to determine the labeled N translocation to current shoots and woody branches of various ages. Even the twelve-inch diameter trunks were chipped and analyzed. This research suggests reducing off-year applications by one-third of the on-year rate. The demand for N and the tree’s capacity to take N up from the soil is greater in the on-year. Nitrogen uptake is largely driven by crop load since nut fill accounts for 90 percent (about 100 pounds,) of the accumulated seasonal nitrogen. Since off-year trees are lower in stored N, one might consider applying half the season’s N prior to shell hardening and the remainder in July and August (Weinbaum, et.al.,1988, 1991,1993,1995,California Pistachio Commission Annual Reports).

For on-year trees, apply between 175 and 200 pounds of actual N depending upon crop load, tree size, vigor and method of application. The most recent findings of Dr. Patrick Brown indicate 28 pounds of actual N are REMOVED from the orchard for every 1,000 pounds of dry, in-shell ACP weight pistachios. Each tree uses about one pound of N. This value DOES NOT take into account inefficiencies in application! As mentioned in last month’s task list, this varies greatly with application method, especially if you are water running on a soil with low infiltration. An additional 25 pounds are required for tree growth. Using Dr. Brown’s values, a 5,000 pound crop would require 140 pounds (5 x 28), plus 25 pounds for the tree itself. That equals 165 pounds at 100 percent application efficiency. We estimate that applications applied through well-maintained, low-volume systems are about 75 percent efficient. Therefore, one has to apply 25 percent more than 165 pounds, or 206 pounds, to meet the requirement of a 5,000-pound crop. Monitoring of leaf tissue and soil levels is then necessary to determine if each is rising or dropping. Rising nitrate nitrogen levels in the soil indicates you are applying more N than the crop is using, and risking its loss past the root zone and into the groundwater. Obviously, soil samples showing a trend in N depletion suggest an increase in fertilization rate is required to balance uptake with availability. Irrigation water must also be sampled for nitrate N and considered in the amount applied, since 10 ppm nitrate nitrogen provides 27 pounds of actual N per acre foot of water applied! Four acre-feet applied seasonally therefore meets most of the requirement of a 4,000-pound crop! Those of you still reading this may be asking, “Why all the talk about nitrogen?” But if you do not begin collecting some data on the ranch to assess your nitrogen program, you will soon find that was a mistake when it comes time to justify your usage with the Regional Water Quality Control Board.

Former UC doctorate student, Ismail Siddiqui, and Dr. Brown have completed a prediction model to correlate May tissue sampling with our traditional August critical values of nitrogen and potassium. These guidelines are based upon extensive research in four high-yielding orchards across California from 2009-2012. These guidelines are based on specific sampling procedures that can be found at this web link: http://ucanr.edu/sites/scri/Assessment_of_Nutrient_Status_in_Pistachio/PPM/. After receiving your tissue results, go to their prediction model (upper right corner on the same page) and enter your N and K values. A 3 percent N and 1.3 percent K level, in May, predicts that your orchard will have 2.62 percent N and 2.01 percent K in August. There is also a PDF file that discusses early-season sampling and in-season nitrogen application for further reading. Adding high levels of N to the soil early in the season does not force the tree into greater uptake unless the tree is deficient. Available data indicates pistachio growth and yield is not improved with July tissue levels above 2.5 percent. (Weinbaum, et.al. 1988, 1995). Plant N uptake is dependent upon root health, water management, soil temperature, crop load, and overall plant demand. Remember, uptake is driven by DEMAND, NOT by you over-feeding the tree!

At present, it is recommended that Nitrogen (N) application through the drip system or by calibrated surface equipment begin in mid- to late-April, during early nut development. A suggested seasonal schedule for a 5,000-pound crop (200 pounds of N) is: 25 in April; 50 in May; 50 in June; and 75 in July. This amount assumes a 75 percent application efficiency AND no nitrate N in the irrigation water.

Additionally, 125 pounds of potassium (K+) is applied annually due to the high potassium requirement of pistachios. A suggested K application schedule is as follows: 50 pounds in May; 50 pounds in June; and 25 pounds in July. These fertilization rates are typically achieved through liquid blends applied through the drip system during May, July, and August. Nitrogen is applied alone in April in the form of UN32. Table 1 provides the details of some commonly used nitrogen and potassium sources.

Table 1. Pistachio Production Nitrogen and Potassium Fertilization Program

Fertilizer Lbs./gallon product Gallons/Ton Product Lbs. Nutrient/Gallon of Product
Nitrogen Potassium
UN32 11.06 181 3.54 0
10-0-10 9.7 206 0.97 0.97
15-0-5 9.7 206 1.46 0.49

Application Date Fertilizer Source Gallons/Acre Lbs. Nitrogen/Ac Lbs. Potassium/ Ac
April UN32 7.0 25 0
May 10-0-10 51.5 50 50
June 10-0-10 51.5 50 50
July 15-0-5 51.5 75 25
Total 200 125

Young Tree Management: Dr. Patrick Brown and Qinglong Zhang were the first researchers to show good zinc uptake at 50 percent leaf expansion (late April to early May). Because leaf out occurred 10 days earlier this season, the cuticular waxes on the leaf surface may be fully developed by early May. Due to high uptake efficiency, only 2 pounds of zinc sulfate, 36 percent, are required. It is safe to also add one-half pound of Copper EDTA or one pound of Solubor to the foliar zinc sulfate rate. Buffering this mixture to a pH of about 5 improves zinc uptake by increasing the amount in solution. Acidification should be done with citric acid (powder) rather than phosphoric buffer to prevent zinc phosphate precipitation. Many growers prefer to avoid the “Betty Crocker” mix and apply liquid materials formulated for pistachios. Check with your supplier for suggestions, but be sure they have adequate amounts of copper, boron, and zinc. This is especially true of two- and three-year-old trees. They may require as many as three foliar treatments to insure continued rapid shoot growth. Deficiencies severely limit canopy development and reduce early bearing potential. Zinc and boron deficiency is the most common problem I diagnose in young tree plantings! The calendar period for treating young orchards is longer than that for mature trees due to the extended period of young, tender growth. High pH soils tend to have more zinc deficiency problems. This soil condition is more the norm than the exception in the pistachio industry!

Growers with second leaf trees should have finished their second training pass by the time they read this. That is right, ALREADY TWO PASSES! I recently talked to the Kern County Tree Training King, and he just shakes his head at people who tell him they are going to wait until the primaries are 24 inches before they make their first pass! There must not be enough oxygen to go around in Bakersfield. They are wasting SO much growth that could be directed into productive secondaries. The first pass would have suckered the rootstock up off the ground about 14 inches. I still recommend pinching the remainder of the rootstock suckers to aid in trunk girth development, but I see that cultural practice is being dropped by many tree trainers.

How about one of you guys doing some rows without stripping to compare tree growth? Maybe we would not have as much “muffin top” overgrowth at the bud union if you left more rootstock growth! Primary branches on trees dormant headed at 42-44 inches have already grown 14 inches long, and they are therefore ready to be pinched back to 11-12 inches. Do not let the primaries get too long! Removing large quantities of shoot growth reduces the number of laterals that push, and costs time for secondary and tertiary growth. Pistachios on vigorous rootstocks grow so fast in warm weather that a training crew pass should be made every 7 to 12 days! In the best orchards, 5 passes are made between late-April and mid-July, when the tipped secondaries are left to grow untipped the remainder of the season. Do NOT tip the tertiaries! It severely reduces branch diameter!

Pest Management: Monitor newly set clusters for evidence of plant bug feeding, which will increase with hotter weather. Drying vegetation near the orchards will soon become unfavorable hosts for plant bugs, and the migration into your pistachios will begin. Many growers minimize this by application of a pyrethroid insecticide in late-April in combination with their foliar nutrient spray. Be sure to watch for false chinch bug activity on weeds within young orchards. . Get rid of the London rocket and spotted spurge now! There are also more reports this year of darkling ground beetle and earwig damage to newly planted trees, so keep those feet in the furrows!

In Memorial: Those new to the pistachio industry will not know the name Paul Couture, but those of us going back to the 1970s sure do. Paul and his wife, Charlotte, of 71 years, always lived on the ranch they established just north of Kettleman City. He planted some of the first pistachios ahead of Leland McCarthy. Paul planted trees on Atlantica in 1969, which were later sold to Charles Keenan, who used them to begin the pistachio business now led by son, Robert. Those trees are still producing today! In 1972, Paul planted more pistachios on the home ranch, which are also still in production and farmed by his children Chris, Steve, and Suzanne. Chris’s daughter, Caitlin, and her husband, Sam, are also continuing the Couture family farm. Paul was a very unassuming fellow, always keeping a low profile, but those who knew him recognized him as a leader and innovator. The Couture family branched out from grapes in 1926 to carrots, asparagus, exotic melons, organic almonds, pomegranates, and pistachios. Paul was third on the original melon packer’s list. Always a gentleman, Paul passed February 2, 2015, at the age of 97. Another pistachio pioneer to thank and remember!

Happy Farming!


Bob Beede, U.C. Farm Advisor, Emeritus