February Pistachio Task List

Robert Beede, U.C. Farm Advisor, Emeritus

Pistachio growers are out pruning trees, destroying overwintering mummies, finishing up their pre-emergent weed treatments, fixing equipment, and assessing what the crop potential is for this season. Let’s do an update together to see where we stand for 2016.

Rain and Irrigation
I have had so many occasions to be out dancing in the rain in my birthday suit that I am tan all over! Wahoo!! Every time it rains, I just stop and watch for a while, and give thanks. When I drive east from the Westside, I get all teary looking up at that wonderful snowpack in the Sierras. It’s so nice to have them white capped again.

If you think the drought is over, check out the reservoir and snowpack status at 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 snowpack is tracking the 30-year average. This is obviously far better than last year, but still much less than the benchmark wet winter of 1982.

Selecting “Reservoirs Status” from my webpage menu can access statewide reservoir conditions. 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. The water in the major reservoirs clearly shows that we are not out of the drought woods yet. Present storage levels range from 21 to 63 percent of their historic levels as of January 21. Several of the large reservoirs have only 15-20 percent of their total capacity. Lake Shasta, representing the highest recipient of rainfall runoff, is at 42 percent of total capacity, but it is 30 percent less than its historic level at this time. So, there is LOTS of room for runoff! You can see why people argue with the Army Corps of Engineers over discharging water now with the reservoirs so low.

Every grower should be out checking soil moisture with an auger to verify soil water content. Yeah, I know it has rained a lot, but do not make any assumptions about your root zone water content. Although pistachio roots can be found much deeper, we routinely use the upper four feet as the effective root zone. To assist you in determining the present water content of your soil, go to this link on my UC website: http://cekings.ucanr.edu/files/19006.pdf. This manuscript is for walnut irrigation, but the appendix describes how to accurately assess soil texture, and how to estimate its present water content using the feel method.

I never rely entirely on instrumentation for soil moisture assessment. I auger to five feet, and use the guidelines in this appendix to assess water content at one-foot increments with my fingers. In doing this, you will find that the results are rarely ambiguous—the soil will either be moist and easily compressed into a ball that holds together when lightly bounced within the palm of your hand, or it will be so dry you can hardly get it out of the hole with the auger.

Good soil moisture in February optimizes early season root development and fully hydrates the tree in preparation for bud break. Enhanced root activity from moist soil may play a hormonal role in stimulating bud break. If the dormancy requirement is fully met by mid-February, pistachios could begin showing green tip by mid-March, if the weather turns warm and dry. This makes it all the more important to have water in the profile prior to bud break. This also allows you to focus on spring fungicide sprays without concern for irrigation. Research indicates that fully canopied pistachios use less than 1.5 inches of water from bud break to April 30, so do not be in a big hurry to irrigate once the trees have fully leafed out.

Chilling Update
CIMIS stations in pistachio production areas statewide report very good chill accumulation using either the below 45°F or Chill Portion Model. As you know, we have migrated away from the traditional use of the below 45°F model, due to the occurrence of fogless, unusually warm days during the past two winters. The solar radiation associated with warm days raises the bud temperatures well above 45°F, and thus they do not contribute to the rest requirement of the tree. We often state that elevated temperature “negates” hours of chill accumulation, but we really do not know what that means.

Some argue that you cannot take away what you have already made. Other researchers suggest that this negation may be more related to the consumption of limited soluble sugars within the bud and adjacent branches, whose concentration is critical to pushing the bud under favorable spring temperatures. I have written previously about the effect high January temperatures have on respiration; an increase of 100 F can double the respiration rate and rapidly deplete the stored carbohydrates. Regardless of the actual physiological mechanism, use of the Chill Portion Model considers these warm temperatures with the intent of providing a more accurate ESTIMATE of effective chilling.

Also known as the Dynamic Model, it calculates chilling hours between 35-55°F in units known as “chill portions.” Dr. Ammon Erez and a team of researchers developed this more sophisticated model in the 1990s to account for temperature variability since it was common in their native country of Israel. Erez et al, theorized that fluctuating warm temperatures inhibit physiological processes associated with satisfaction of deciduous tree rest. Rather than canceling chill portions already created, Dr. Erez suggests that warm weather prevents the creation of additional chill portions. So, even if there WERE temperatures below 45°F, for a given day, the existence of warm daytime temperatures negates their effect on rest development, and thus a chill portion is not created.

Based upon past research found in the pistachio industry annual reports, it is estimated that the Kerman cultivar needs about 750 hours and Peters needs about 850 hours for normal bloom. Using the traditional below 45°F chilling accumulation model, we could conclude that as of January 21 the rest requirement of Kerman and Peters has been nearly satisfied this winter in most growing regions. The warmest location (Coalinga) has 690 hours below the 45°F threshold, and Blackwells Corner has 889. Most stations report in excess of 800 hours below 45°F. This is well above what was accumulated last year at this date, and most of these hours are effective, due to the cloud cover present this winter.

Dr. Katherine Pope, Yolo County Farm Advisor and doctoral candidate, was funded by the pistachio industry to test the validity of the Chill Portion Model. Although the results were not as conclusive as she hoped, Dr. Pope’s data suggest that Kerman pistachios require about 58 chill portions to prevent yield reduction from inadequate rest. Peters blooms best at about 61 or greater chill portions. I have prepared Table 1 to contrast the Chill Portion accumulation this season, as of January 21, with that of previous years on the same date. The values in parentheses are the total number of Chill Portions accumulated from September 1 to February 15. As you can see, we are well ahead of last year, and with three more weeks remaining in our traditional chill accumulation period, we could very likely get rest completely satisfied. Presently, we are accumulating about five Chill Portions weekly, so at that rate we could have 70 Chill Portions in many locations by February 15. This would equal 2010, our last good chilling winter.

Table 1. Chill portion accumulation for various CIMIS stations statewide from 9/1-1/21 for selected years.

Numbers in parentheses are the total chill portions accumulated at each station by year from 9/1- 2/15. By RH Beede.

Year 2015 2014 2013 2010
Durham 55 46(55) 43 (54) 58 (70)
Patterson 47 52 (63) 48 (63) 56 (73)
Madera II 53 42 (52) 43 (57) (NA)
Parlier 55 53 (64) 43 (53) 57 (74)
Five Points 51 42 (52) 43 (55) 54 (69)
Coalinga 51 39 (48) 44 (53) 56 (70)
Shafter 50 52 (61) 49 (63) 52 (70)
Delano 53 45 (58) 45 (56) 55 (73)
Blackwell’s Corner 52 42 (52) 41 (50) 58 (75)
Arvin/Edison 50 36 (44) 46 (55) 51 (66)
Porterville 59 48 (63) 46 (59) 50 (63)

What about Using Oil This Year?
Oil? This year? Are you NUTS?? Your poor pistachio trees are just getting out of rehab, and you want to wave the sauce under their noses? All I heard last year was how growers got robbed of what little crop they could have had if they had not oiled. So, in case you do not understand California COOL, the answer to this question is, NO! NO OIL! Take what you get this year and give thanks. Besides, with all this good chilling, we might have a tremendous crop, and THEN the complaint will be about what to do with 700 million pounds of puny pistachios!

Speaking of potential crop, now is the time to go LOOK at your trees to see how large and abundant the flower buds are. I have seen some barn busters out there. This is in contrast to a recent tour Chris Wylie, Agri-World ranch manager, did with some other Westside growers. They saw several blocks where the flower buds had tripped off, even after a tiny crop last year! Now, do not ask me WHY, ‘cause I do not know, and I am not going to try and wax on poetically about what MIGHT be going on, because it would all be phony baloney. Regardless of the cause, go look at your trees to see what their fruiting status is potentially.

Scale Management
Soft scale should be treated before the “rubber stage,” which usually occurs by the third week of February. Recommended treatment is 4-5 quarts of Sevin XLR plus 4 6 gallons of oil depending on scale severity. Oil alone is probably enough in most situations unless they look like beads lined up on much of the one-year-old wood. Seize 35W or Assail are effective alternatives to Sevin plus oil, and eliminates the rest breaking effect. Like I said earlier, I would not oil for any reason this year!

NOW Management
The 2015 crop was generally very clean and will be easily marketed by the processors. Part of the low NOW damage was associated with the high closed-shell. There were fewer nuts to infect and build the population. Even if the 2016 crop size is large, grower prices are strongly affected by nut quality. Poor quality puts the processors up against the “worm ropes” as they try to make bad nuts into good ones.

Processors are already offering considerable bonus incentives to keep the worms out of the plant. If you do not think quality is critical for your industry, then you are part of the problem, not the solution! Regardless of what others say, I will go down with the ship preaching that winter sanitation is the cornerstone for effective NOW control. It is very important that growers blow the berms and destroy over wintering nut mummies as best as they can to minimize NOW survival. The rains are going to help with nut removal and molding, but NOW love a moldy nut! It is preferable to shred knocked mummies, but disking is better than leaving them undisturbed on the orchard floor. This is critical in orchards suffering from high NOW populations. Insect damaged nuts are a major concern to foreign buyers because of their unsightly appearance and greater susceptibility to aflatoxin producing molds. Sanitation also helps reduce BOT inoculum, which can splash up into the trees during heavy storms. Remember: we want all diamonds in the bags, so the consumer keeps shelling out the shekels!

BOT Management
During pruning, keep looking for Botryosphaeria. Wood infections remain capable of releasing inoculum for six years! So, if growers do not cut it out during the winter, it will build up and bite them again.

I would also collect a couple hundred fruit buds and cut them in half to see if they are black. Black buds are most likely infected with BOT. As you collect them, look for dead one-year-old shoots and black fruit rachises that do not knock off the tree easily. Cut into the base of these shoots or rachises to see if there is a black streak in the limb extending beyond the base.

Wood damaged from cold also has a black zone between the live and dead wood, but its margin is very sharp and does not run into the limb. Ignoring these symptoms allows inoculum levels to build and overwintering cankers to increase. During wet springs, tremendous quantities of spores will be spread throughout the orchard, so many that even the most intensive fungicide program will be unable to prevent major cluster infection and crop loss. Reduce the threat of this disease by getting rid of as much overwintering infections as possible.

Remember, it is a numbers game. The lower the inoculum, the less risk you have of major crop loss. Happy farming! We look forward to seeing the American Pistachio Growers in Palm Desert!