- Author: Houston Wilson
- Author: Jhalendra Rijal
- Author: David Haviland
Crop sanitation will be key to controlling the invasive carpophilus beetle
Growers and pest control advisers (PCAs) should be on the lookout for a new pest called carpophilus beetle (Carpophilus truncatus). This pest was recently found infesting almonds and pistachios in the San Joaquin Valley, and is recognized as one of the top two pests of almond production in Australia. Damage occurs when adults and larvae feed directly on the kernel, causing reductions in both yield and quality.
Populations of carpophilus beetle were first detected in September in almond and pistachio orchards by University of California Cooperative Extension Specialist Houston Wilson of UC Riverside's Department of Entomology. Pest identification was subsequently confirmed by the California Department of Food and Agriculture.
Wilson is now working with Jhalendra Rijal, UC integrated pest management advisor, North San Joaquin Valley; David Haviland, UCCE farm advisor, Kern County; and other UCCE farm advisors to conduct a broader survey of orchards throughout the San Joaquin Valley to determine the extent of the outbreak.
To date, almond or pistachio orchards infested by carpophilus beetle have been confirmed in Stanislaus, Merced, Madera and Kings counties, suggesting that the establishment of this new pest is already widespread. In fact, some specimens from Merced County were from collections that were made in 2022, suggesting that the pest has been present in the San Joaquin Valley for at least a year already.
“It has likely been here for a few years based on the damage we've seen," Rijal said.
This invasive beetle overwinters in remnant nuts (i.e. mummy nuts) that are left in the tree or on the ground following the previous year's harvest. Adults move onto new crop nuts around hull-split, where they deposit their eggs directly onto the nut. The larvae that emerge feed on the developing kernels, leaving the almond kernel packed with a fine powdery mix of nutmeat and frass that is sometimes accompanied by an oval-shaped tunnel.
Carpophilus beetle has been well-established in Australia for over 10 years, where it is considered a key pest of almonds. More recently, the beetle was reported from walnuts in Argentina and Italy as well. Carpophilus truncatus is a close relative to other beetles in the genus Carpophilus, such as the driedfruit beetle (C. hemipterus) that is known primarily as a postharvest pest of figs and raisins in California.
Monitoring for carpophilus beetle is currently limited to direct inspection of hull split nuts for the presence of feeding holes and/or larvae or adult beetles. A new pheromone lure that is being developed in Australia may soon provide a better monitoring tool for growers, PCAs and researchers.
“We're lucky to have colleagues abroad that have already been hammering away at this pest for almost a decade,” said Haviland. “Hopefully we can learn from their experiences and quickly get this new beetle under control.”
The ability to use insecticides to control carpophilus beetle remains unclear. The majority of the beetle's life cycle is spent protected inside the nut, with relatively short windows of opportunity available to attack the adults while they are exposed. The location of the beetles within the nut throughout most of their life cycle also allows them to avoid meaningful levels of biological control.
In the absence of clear chemical or biological control strategies, the most important tool for managing this beetle is crop sanitation.
“Given that this pest overwinters on remnant nuts, similar to navel orangeworm, crop sanitation will be fundamental to controlling it,” Wilson said. “If you needed another reason to clean up and destroy mummy nuts – this is it.”
In Australia, sanitation is currently the primary method for managing this pest. And here in California, new research and extension activities focused on carpophilus beetle are currently in the works.
“It's important that we get on top of this immediately,” said Wilson. “We're already starting to put together a game plan for research and extension in 2024 and beyond.”
If you suspect that you have this beetle in your orchard, please contact your local UC Cooperative Extension farm advisor (https://ucanr.edu/About/Locations/), County Agricultural Commissioner (https://cacasa.org/county/) and/or the CDFA Pest Hotline (https://www.cdfa.ca.gov/plant/reportapest/) at 1-800-491-1899.
/h3>- Author: Phoebe Gordon
- Author: Seth Watkins
- Author: Caleb Crawford
- Author: Elizabeth J Fichtner,
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Pistachio production has been expanding, particularly into marginal soils with high salts, boron, and even sodic conditions. One plant that is endemic to these conditions, alkaliweed, has been reported in these orchards. While there have been some articles suggesting that it it is a new weed to pistachio production, I am personally a bit skeptical of this, as it is endemic to the American Southwest, found as far south as Baja California, as far east as Texas, and has been reported in Ecuador, Argentina, and Chile. What is more likely is that pistachio production has been expanding into more marginal lands that already contain alkaliweed, and has been noticed more due to its extraordinary and frankly admirable ability to resist control with herbicides. However, this is speculation on my part – I very well may be proven wrong in the future.
Alkaliweed is a member of the morning glory family (Convolvulaceae), the same family as field bindweed. Similar to field bindweed, it is a plant that spreads via rhizomes (underground stems that can sprout new shoots and roots), and can spread and propagate asexually. Though there are ecological records of bindweed, we know very little about this plant. We have observed alkaliweed flowering profusely in agricultural settings, but in our own personal observations, in combination with those of a former Fresno State graduate student, James Schaeffer, we have not seen any seed production. It is often, but not always, found growing by itself in an orchard. We have also observed some sort of rust fungus growing on the underside of the leaves at all three of our research sites, though some sites seem to be more heavily impacted. It is unknown if this rust is found in non-orchard areas, or if it negatively impacts alkaliweed growth.
Alkaliweed gets its name based on the salty conditions it thrives in, which can be coastal areas as well as the arid southwestern San Joaquin Valley. Work done by James Schaeffer has shown that seed germination is highly tolerant of a wide range of soil pH levels as well as soil salinity; seed germination studies done in petri dishes showed that seed germination was uninhibited until 16 dS/m.
Alkaliweed is a small plant. It can either be fairly prostrate in its growth habit and reaching no more than an inch or two above the soil surface (Image 1a), or more upright, for a maximum height of approximately six inches (Image 1b). Individual plantlets are no more than 6 to 8 inches in diameter, and attempts at excavating it have shown that it seems to be connected to a deeper, more extensive rooting/rhizome system. The leaves are only a few millimeters across, green when they first emerge from the soil, and silvery-grey when older, due to leaf hairs on the surface of the leaf (trichomes). Flowers are borne at the base of an axil, and are just as tiny and as plentiful as the leaves (Image 1b). It has an uneven distribution in orchards; orchards with alkaliweed do not tend to be entirely infested, but rather have patches of heavy infestation and patches free of alkaliweed. It has been observed in monoculture type conditions as well as with other weeds – we do not know if it outcompetes other weeds or is so hard to kill that it ends up being the only weed left in an area.
Conversations with growers and other weed scientists have indicated that it is extremely difficult to control; our collaborators and fellow researchers have stated that no chemicals or cultural control methods seem to kill it. It was for this reason that we embarked on this research trial.
We conducted this trial at three different sites across the Southern San Joaquin Valley in 2021: a non-bearing orchard in Tulare County, and two bearing orchards in Kings and Fresno Counties. We chose areas within each orchard that were more heavily infested, and there were differences in how dominant alkaliweed was in the treated areas. The Fresno site was almost entirely composed of alkaliweed. The Tulare site was predominately alkaliweed but did have some alkali mallow present, and the Kings site had a more diverse mix of weeds, but was still dominated by alkaliweed.
We examined nine different herbicide treatments, and one untreated control (Table 1). Three of the treatments were glyphosate with different adjuvants; a nonionic fatty acid surfactant (Rainier-EA); or a silicone-based nonionic surfactant, with an ammonium-containing salt to stabilize the glyphosate. An additional treatment added glufosinate to the glyphosate+fatty acid surfactant. We examined three different sulfonylurea herbicides: halosulfuron, flazasulfuron, and rimsulfuron. All are phloem translocated herbicides that are effective at controlling broadleaved weeds, with some activity on sedges (halosulfuron, limited ability for rimsulfuron) or grasses (flazasulfuron, rimsulfuron). All were combined with a crop oil concentrate to increase penetration. Lastly, we looked at two different 2,4-D formulations: the traditional amine form and a choline formulation, which has a lower volatility than the amine formulation.
We applied these products three times: late-May of 2021, early November in 2021, and mid-April in 2022. All sites were evaluated based on percent control in 2021. In 2022, the Tulare and Kings site were also rated as percent control. The Fresno County site was rated on percent groundcover (again: alkaliweed was the only weed present at this site) to try to take into account any residual effects from the previous year. The Tulare and Kings sites were also rated based on percent weed groundcover for the last site rating.
While there were significant differences across sites in 2021, none of the products adequately controlled alkaliweed after one application, though some products did have a fairly effective short-term burndown efficacy. In 2021, the 2,4-D choline treatment controlled alkaliweed significantly better than the control at all three sites (Figures 3, 4, 5), sometimes much better than the control. Alkaliweed response to glyphosate was variable, but generally this herbicide had less long-term control than 2,4-D (Figures 3, 4, 5). Glyphosate was ineffective at controlling alkaliweed at the Fresno site in 2021 (Figure 5).
Two additional herbicide applications partially controlled alkaliweed only at the Tulare site. Alkaliweed was poorly controlled at the Fresno and the Kings site. With the exception of rimsulfuron, applying an herbicide significantly increased alkaliweed control (Figure 6). The 2,4-D formulations and the glyphosate tank mixes without glufosinate were generally the best at controlling this perennial weed. The same was true 5WAT at the Fresno site (Figure 8), however the significant effects disappeared at later measurement dates (data not shown). For the most part, there were no significant differences between treatments at the Kings site in 2022 (Figure 7).
The research unfortunately does not show a slam dunk when it comes to alkaliweed control. At this point, 2,4-D seems to be the best choice, though glyphosate seems to have some effect. It is possible that yearly applications of 2,4-D, glyphosate, or a rotation of the two would result in underground storage organs becoming depleted of energy, eventually killing the plant, though this would need to be tested.
An added complication is that we were spraying small plots – a larger experiment that covers more land may reveal better control.
More work is being done to better understand the biology of alkaliweed. Stay tuned for more updates!
Thank you to our cooperators.
Phoebe Gordon, Caleb Crawford, Elizabeth Fichtner, and Doug Amaral are UC Cooperative Extension. Seth Watkins and Brad Hanson are with UC Davis.
- Author: Trina Kleist, UC Davis
Growers invited to participate in study by sharing their experiences
A multi-state team led by Patrick J. Brown has been awarded nearly $3.8 million over the next four years for a project to improve pistachio production as the industry faces warmer winters and scarcer water.
“We are at this unique point in history where we can do this,” said Brown, an associate professor in the UC Davis Department of Plant Sciences.
The project aims to ensure the industry can thrive in coming decades despite the challenges faced. Growers are invited to participate in the study, sharing what they already are trying in their own fields or supporting any aspect of the project. To discuss the possibilities, contact Brown at pjbrown@ucdavis.edu or (530) 752-4288.
The project includes research to ensure pollination, experiments to calculate irrigation needs amid water shortages, creating tools to improve public breeding programs, developing more efficient harvesting equipment, and economic analyses to ensure future pistachio cultivation is economically rewarding. Researchers hope to offer a guide for growers deciding whether to plant new orchards or remove existing ones.
“The success of California's pistachio industry, which is the top producer of the nuts in the world, has always relied on a strong collaboration between UC researchers and pistachio growers,” said project participant Florent Trouillas, a UC Cooperative Extension specialist in the UC Davis Department of Plant Pathology. “Research efforts must continue to address enduring and new challenges, improve sustainability and ensure the profitability of pistachio farming.”
The tasty, green nuts have blossomed into a $5.2-billion industry in California, thanks to their greater tolerance of dry lands and salty soils. The project aims to further improve their climate resilience by finding a rootstock that can thrive despite growing water scarcity and declining water quality projected over the next half-century. With millions of genetically distinct pistachio trees growing in the state, "we already have out there what may be the industry's next great rootstock," Brown said. "It's probably in some grower's field already. We just have to find it."
Researchers seek to pair that new rootstock with high-yielding scions – the producing part of the tree grafted onto the rootstock – to develop new combinations that can thrive in the different conditions across the state.
Trouble with “boy meets girl”
Pistachios, like many other tree crops, have male and female trees, and they require hundreds of hours of wintertime temperatures below 45 degrees Fahrenheit for the trees to flower in the spring. Wind blows the pollen from male flowers to female flowers, creating nuts.
Complicating the timing: Boy flowers and girl flowers generally require different amounts of winter cold to bloom. After a sufficiently cold winter, boys and girls flower together. But if the winter is warm, most of them will flower at different times, reducing pollination.
That happened in the winter of 2014-15, which saw unusually warm winter temperatures. The following fall, farmers harvested only half their expected crop, losing more than $1 billion, Brown said. Climate change is expected to provoke progressively warmer winters in the future, on average.
An additional complication: The boy scions come from a single variety, or cultivar, and the girl scions come from another single cultivar. "In California part of the problem is that we have been relying on a single male and single female cultivar," Brown explained.
A key part of this project will be to test new scions that can pollinate efficiently despite warmer winters. “We now have additional male and female scions released in the last 10 to 15 years, but we need more information on their chill requirements,” Brown said.
Growing importance of pistachio sector
With nearly 520,000 acres planted in California in 2021, pistachios are the fastest-growing tree nut crop in the state. Growers have doubled their plantings over the past decade, due to pistachios' drought tolerance and higher gross returns compared to other nuts, experts report. California dominates the industry, growing 99 percent of the nation's crop and nearly 60 percent of the world's crop, employing people in 47,000 full-time-equivalent jobs and creating $5.2-billion of total economic impact in 2020, according to American Pistachio Growers.
Brown's team is part of a wider effort at UC Davis to support the sector's growth and adaptation to climate change. Other department members participating in the project include co-directors Louise Ferguson, a UC Cooperative Extension pomologist, and Richard W. Michelmore, a distinguished professor and director of the UC Davis Genome Center. Also participating are Giulia Marino, a UC Cooperative Extension specialist; and Grey Monroe, an assistant professor.
Other UC Davis participants include Trouillas and Brittney Goodrich, a UC Cooperative Extension specialist in the Department of Agricultural and Resource Economics. The project also includes researchers from UC Merced, New Mexico State University and Purdue University.
The four-year project was among nearly $70 million in Specialty Crop Research Initiative grants awarded this fall by the National Institute of Food and Agriculture. The Department of Plant Sciences landed three of the 25 grants.
Read the NIFA grant summary.
/h3>/h3>/h3>- Author: Blake L Sanden
- Contact: Blake Sanden
- Editor: Julia Stover
Blogs 1 and 2 from May and June were rather complicated discussions of remote sensing imagery (focusing mostly on CERES images of these pistachio demo fields) and why the red (dry) to blue (wet) colorized image scale doesn't always remain constant from one image event to the next.
BOTTOM LINE: for any given image, the color separation across the field of red to blue is always showing the true relative drier to wetter areas of the field on that date. So many different colors across the block means the water status of the trees is quite variable. You want 90% of the field to be green and blue. BUT depending on the spread of canopy temperature (hottest to coolest areas) over the field on a given date some trees that showed up as green the month before might show up as yellow for the current month – even though the actual canopy temperature in degrees and a ground-based pressure bomb stem water potential (SWP) measured on the same trees are the same for both images. Both images provide valuable information for that date – especially on field uniformity – but for an absolute verification of the degree of real tree stress, you need additional ground data. Using this data, we verified that all fields were successfully winter/spring recharged with sufficient root zone soil moisture. So for this BLOG we are looking at the combined data snapshot for our fields from 6/19/2020.
PRESSURE BOMB COMPARISON ACROSS ALL FIELDS
The above figure for 2020 shows that the non-saline Eastside and Westside fields are closer than they were for 2019. As of June, the semi-saline Mid Salt site is about -2 bars more SWP stress than the non-saline fields and the saline HiSalt site is about -4 bars more stress. This is NOT for lack of water but the result of the additional salt-caused osmotic resistance to water uptake.
NON-SALINE EASTSIDE FIELD
AERIAL IMAGERY: This makes for good feeling as the fields are nearly all blue and green in all the fields, and we have -10 to -11 bars SWP in the west and SE fields (numbers in white) – so we are good to go! But wait, we have a -15 bar SWP in the NE field, which indicates stress. This was not obvious from looking at the trees and this field was irrigated with almost exactly the same amount of water as the other fields
TREE STRESS: Using the tree as the continuous integrated moisture sensor is somewhat possible using a dendrometer that measures the real-time daily shrink/swell and growth of the tree. The Phytech company is helping us do that by generating this average growth information in the below figure over 3 trees instrumented with dendrometers:
This is exactly the pattern that you want to see – steadily increasing growth running 15-30 microns/day over the spring and early summer. From Mid-June to July 17 these trees averaged 6000 microns (6 mm) additional radial growth. That's a 12 mm, or almost ½ inch increase in trunk diameter. The blue bars indicate the timing and duration of irrigation of this high frequency double-line drip system.
So what about the -15 bar SWP stress we measured on the NE block? We are fortunate to have 3 dendrometers on this block also which show a similar steady growth increase as the west 80 acres, but the slope is a little less so we only get 4000 microns increased growth (10-20/day) instead of the 6000 we have in the west 80 acres. This would confirm a bit more water stress in this block but not a big deal.
SOIL MOISTURE:
The ROOTZONE SUM chart below from the Jain Logic monitoring system using a Sentek Drill & Drop capacitance probe that measures soil moisture to a depth of 46 inches shows that the total root zone soil moisture has increased about 10% since the start of May. The numbers on the left access are the sum of the percent soil moisture measured by each sensor placed every 4 inches. If these numbers were absolutely accurate, it would mean that this Nord Series fine sandy loam soil would hold 42% water (5.0”/ft) at field capacity, which is impossibly high. The correct number is about 28%, 3.4 inches/foot as measured by a neutron probe. But the good news is that the trends in increased and decreased water content are very real and dependable. So the infiltration chart (below right) is an accurate
indicator of how deep water penetrates (dark blue columns) every irrigation. This shows that the water only went to 46” a total of four times over 3 months, so there is virtually no deep percolation lost below the root zone.
NON-SALINE WESTSIDE FIELD
AERIAL IMAGERY: Okay, this picture makes me feel a little more stressed than the Eastside CERES image – less blue and more yellow and red. The SWP (numbers in white) are only -1 to -1.5 bars more negative (stressed) then the eastside SWP and this block did receive about 1.4 inch less water since 5/16 than the Eastside. This is also a 300 acre block with ½ mile rows N to S with only 2 hose runs of ¼ mile each that appear to show weak pressure and water delivery in the middle and at the N and S sides of this block.
TREE STRESS: Unfortunately, cell phone/web reception at this field is not good and only a little of the Phytech dendrometers data came through. However, the 4 days data show as good of growth as the best Eastside block.
SOIL MOISTURE: We have two sites in this field with instrumentation. The NO COVER site below is 80 rows east of the west edge of the field with the soil classed as a Cerrini sandy loam. The soil at this site is sandier than the Eastside field. The irrigation system is a single-line drip with four 1 gallon/hr drippers per tree. Irrigation is typically a 24 hr set every other day starting in June. The Root Zone Sum chart shows a fairly steady water content, but the Infiltration chart on the right shows that 5 straight irrigations in mid-June penetrated to 46”, indicating possible deep percolation earlier.
The COVER crop site is 30 rows from the eastern edge of the field and is a Calflax clay loam with a definitely higher water holding capacity than the Cerrini SL in the NO_COVER area. This location and the NO_COVER location are in the same irrigation set, receiving water at the same time and duration – typically 24 hours. But with a heavier soil, this site is showing water infiltrating nearly every irrigation as opposed to the sandy loam area just 50 rows to the east. There is possibly a crack adjacent to a dripper that connects with the Sentek probe and pipes water down the side. Of all the sites to have a failure in the Phytech dendrometers, this was possibly the worst one, and these trees did receive 1 inch less water over the last month than the Eastside.
SEMI-SALINE, SALINE LEMOORE FIELD
AERIAL IMAGERY: As expected, the significant variability in canopy growth caused by excess salt and poor soil structure in this field produces the lowest and most variable Normalized Differential Vegetative Index (NDVI, left) and more WATER STRESS than in any other field. Should more leaching have been done during the winter to further reduce root zone salt loads? Perhaps the grower could have done more, but he applied 10 inches during the winter, which takes forever to penetrate in this saline-sodic Lethent silty clay loam, and his June 2020 SWP was less negative than June 2019. This is square quarter-section field with a double-line high frequency automated drip system with two ¼ mile hose runs, running in 3 to 8 hour sets. There is a distinct stress patter along the hose ends in the center and N and S borders of this field very similar to what we saw in the non-saline westside field with similar length of hose run. These are all pressure compensated drip emitters and any time I have checked the pressure at the hose end it is >12 psi which should be sufficient for max flow. So I'm guessing more emitters just get clogged and don't clean out during flushing. Maybe it would help to increase filter station/booster pressure and flush hoses more often. The grower used to run longer sets but that exacerbated the waterlogging problem.
TREE STRESS, SEMI-SALINE: Even though there is definite canopy size, ET and yield reduction in the best semi-saline area of this block compared to our non-saline fields, there was still excellent growth recorded by the Phytech dendrometers from May to July. In fact, the three trees with dendrometers in the NE area (D05) of this block have put on an average 10,000 microns (10 mm) additional radial growth. That's a 20 mm, or ¾ inch increase in trunk diameter – the highest growth rate of all our monitoring sites even with extra stress from the salt! Must be the seaweed extract Bart uses, hmmm.
TREE STRESS, SALINE: This severely affected saline area in the south central part of the block surprised us last year with about half the growth of the D05 Area. But this year has had essentially ZERO growth
SOIL MOISTURE, SEMI-SALINE: The second highest total Root Zone Summed water content is this area – reflecting a soil texture finer than any of the non-saline problem fields and very slow drainage through the profile. The deepest penetration during an irrigation is only 18”. The impact of this anoxia, waterlogging, has just as much negative impact on pistachio growth as does the higher salinity.
SOIL MOISTURE, SALINE: The highest total Root Zone Summed water content is in this area (D03) of the field. Frequently prone to ponding many trees have died here. The deepest recorded irrigation penetration for any 3 to 8 hour event is 6”. Installing an automated WiseCon irrigation system to run very short sets as often as daily has been the best strategy the grower found to reduce anaerobic conditions in the root zone and improve tree growth.
- Author: Blake Sanden
- Contact: Blake Sanden
- Editor: Julia Stover
This is the second BLOG for our 2020 Pistachio Irrigation Demo where we will attempt to put up relevant data and images to help growers see alternative monitoring methods in action over 3 different mature pistachio production orchards from Eastside to Westside, non-saline to saline soils. This DEMO BLOG is intended not only to give you easy to digest summary irrigation management snapshots, but also allow for your feedback/questions which I will attempt to address as time allows. Fortunately, none of these Demo orchards had blanking problems this spring. For a summary of yield, applied water and tree stress (using the pressure chamber to measure stem water potential, SWP) for 2019 go to the website hosted by the UCD FNRIC.
For this second BLOG we are going to focus on the Eastside non-saline orchard only and revisit the CERES remote sensing aerial imagery of tree water stress (calculated from the canopy temperature as determined by infrared camera) and Normalized Differential Vegetative Index (NDVI, basically a plant volume and vigor estimate calculated from a normalized ratio of near infrared reflectance over the entire infrared spectrum). In BLOG 1 we looked at how the last image just before harvest (9/6/2019) compares with just a couple weeks ago (4/25/2020) and how the in-field ground-based stem water potential (SWP) pressure bomb readings compare. This is where interpreting this kind of imagery gets tricky…
Point 1, adequacy of winter recharge: Like most pistachios in the SJV this orchard gets a couple inches post-harvest irrigation and is then cutoff to dry down the trees before winter to avoid frost damage. Jain Logic is supporting this Demo Monitoring project with 5 sites across the 3 orchards we monitor. Using Sentek Drill & Drop capacitance soil moisture probes they continuously monitor stored soil water and when the system is pressurized. Lots of analyses are available. The intro to each site looks like this:
Below is a larger chart showing rootzone soil moisture from 11/1/2019 to 6/17/2020. The blue zone is field capacity (“Wet”) and the gray zone is “Dry”. The grower maintained the old flood system which was used around 2/10 to get the 6” recharge spike shown below. The bottom chart shows the calculated inches applied by the hours run and pressure in the hose. So recharge was good by mid-February.
Point 2, leaf expansion-NDVI: CERES changed the NDVI color scheme from last year to increase the contrast resolution so the red and yellow now correspond to last year's least green more open areas. Eventually, CERES is going to provide numbers to go with these images, but my eyeball calculator says that the 4/25/2020 NDVI in the Eastside west 80 acres is less than the NDVI in the 9/6/2019 image. This makes sense because as of 4/25 the full leaf expansion was about 75% -- so smaller leaves and no cluster weight pulling branches down like in the 9/6 image means that the trees appear to have a lower density of foliage in the aerial image.
CERES IMAGING NDVI & THERMAL WATER STRESS (9/6/2019, 4/25/2020, 5/16,2020)
By 5/16 (below image) the leaves are 100% expanded (but the branches/canopy cover is not bowed down by crop weight) and the “stress” image shows a little more blue than 4/25, but still a lot less blue than 9/6 when the pressure bomb leaf measured stem water potential (SWP) was more negative (more stressed) than the spring SWPs shown in these images. The SE cover cropped field still dominates the color scale with the most blue and green.
Point 3, Accuracy of Water Stress and relative color scheme: Comparing the Water Stress images from September to April is like a slap in the face! Your first thought is, “Wow, these fields were not sufficiently pre-irrigated to refill the profile and there is less water in the rootzone then there was right before the 2019 harvest!” But this is not true. Compare the SWP readings I show in white for 9/6 versus 4/25 and 5/16. These ground-based tree readings ran -12 to -16 bars on 9/6/2019 (-14 bars is moderate stress). But for 4/25 and 5/16/2020 these numbers are much less negative at -7 to -11 bars, which is what you want to see – no stress during the spring push. But why is there much less blue (least stress color) in west 80 acres for the 4/25 image compared to the 9/6 image? Unfortunately, this an artifact of the automatic coloring legend used by CERES at this time. For any given image they calculate a type of crop water stress index (CWSI) using the NDVI cover, humidity, some standard “stress” temperature and most importantly the canopy temp for each pixels from the warmest to coolest then they create a frequency distribution to show the range of stress across the field – coolest as blue, hot is red. This colorized scheme is an accurate representation of the relative variability in canopy temperature/stress at that time for all 3 fields in this quarter section, but it is not an absolute measure of real plant stress, like the SWP number from the pressure bomb, that can be compared across different images. It is also important to remember that SWP and actual ET are NOT the same thing nor are they linearly related. Three “water stress” images for the western 80 acre field (which is our main monitoring effort) are shown below. The 7/18/2019 and 4/25/2020 showed similar SWP readings but the color scale of the 4/25 image shows more stress.
The below charts show what the canopy temp/CWSI “water stress” frequency distributions looks like when calculated separately for the cover crop SE 40 acres vs the non-cover crop W 80 and NE 40 acres. For the 7/18 image you can see that the peaks of each area are close together and have a similar spread, so almost everything is blue and green. But for 4/25 the differences in CWSI between these two areas has a much bigger spread, with virtually all the SE 40 pixels falling in the BLUE zone and almost all the NW 120 pixels falling in the GREEN, YELLOW, and RED zones.
Canopy temperature (CWSI) frequency distributions for NW 120 ac Non-Cover (W-80, NE-40) and SE 40 ac Cover
The below left hand image shows the “water stress” color scale recalibrated for the Non-cover and Cover fields on a separate field basis instead of for the whole quarter section – compared to the original single scale distribution, right.
Point 4, Need for a constant calibration and numeric evaluation across dates and fields: So is it necessary that imagery gives me a constant color scale and numeric evaluation of stress across the whole season and all my fields? For simply looking at the snapshot of field stress uniformity and seeing where the problem areas are the answer is NO. Obviously, the high resolution (0.5-1 ft/pixel) CERES images are some of the best out there for zeroing in on the crop and eliminating a lot of the dirt/floor background. But in my book you need some kind of database/Excel spreadsheet record with a constant value scale that can be analyzed to tell you if that field is improving, getting worse, or falling behind your other fields on the same soil type. Constant color images to flip through would be the final icing on the cake. CERES is making efforts in this direction. But as of right now, for this purposes of this Pistachio Irrigation Monitoring Demonstration, Agralogic, Ltd is bundling their HyperView/HyperGrow service with Jain Logic customers using various satellite platforms to supply growers with weekly Excel table field ET and uniformity updates. The field apparent ET is calculated using infrared canopy temperature and other atmospheric variables from satellite overpass images that occur every 5 to 10 days. This generates the numbers reported to growers and constant color-scale (shades of light to dark blue) images. The downside here is that your pixel/data resolution is now 10-30 m (33 to 100 feet, only one thousandth the data density of CERES images), includes the dirt between the rows and of course can have problems with cloud interference. I feel like their ET data is reasonably in the ballpark, but their uniformity numbers are on the high side when compared with CERES images – but of course you have much less data per field where every pixel is 1.5 to 4 trees across 2 rows, so this kind of averaging will dampen tree to tree variability but may be valid when comparing one or two acres in the SW to a couple acres in the NW of an 80 acre field.
The white areas in the below images indicate the parts of the field obscured by cloud cover – so no data.