Use of ProgGibb LV Plus® Plant Growth Regulator Increases Total Yield/ Fruit Size of Hass Avocados
As of March 27, 2018, foliar application of GA3 (ProGibb LV Plus®, Valent BioSciences, Corp.) to ‘Hass' avocado trees in commercial orchards has been approved. Dr. Carol J. Lovatt, emerita professor of plant physiology at the University of California – Riverside, recently completed research concerning the effectiveness of ProGibb LV Plus® on avocado fruit size and yield. A summary of her research — including best practices — follows.
Application Best Practices
ProGibb LV Plus® should be applied as a foliar spray when 50 percent of the trees in a block are at the cauliflower stage of inflorescence. If a grower cannot make an application at this time, it is best to apply the spray later, rather than earlier in order to ensure effectiveness.
The spray should be applied like a pesticide spray — full canopy coverage with a focus on the inflorescences. Those applying the spray should avoid spraying to run-off.
The ideal dilution for ground application is 12.5 fluid ounces of ProGibb LV Plus® (25 grams active ingredient [gai]) per 100 gallons of water/acre. For aerial application, use 12.5 fluid ounces (25 gai) in 75 gallons of water/acre. According to the research, the ideal application rate is 25g GA3 per acre; higher and lower doses were less effective. The pH of the water used should be adjusted such that the final pH of the spray solution is between pH 5.5 – 6.0.
Dr. Lovatt utilized organosilicone surfactant Silwett L-77® or Widespread Max® at a concentration of 0.05 percent as a wetting agent. Similar pure organosilicone type surfactants would be acceptable as wetting agents. It is important to note that until additional research can be conducted, other materials should not be included in the ProGibb LV Plus® spray solution.
Effect of ProGibb LV Plus® (GA3)
Dr. Lovatt's research team tested the effect of ProGibb LV Plus® on fruit size and yield for both ground and aerial applications. Overall, the research team noted that GA3 had no negative effects on ‘Hass' avocado fruit quality.
Ground applications were tested in March at groves located in Corona, Irvine and Somis, California. The tests were run on Duke 7 clonal rootstock trees at the cauliflower stage of inflorescence development. Each of the groves reported net increases in total yield and large/commercially valuable size fruit. The results were as follows:
Table 1. Effect of GA3 (25 g ai/acre) applied at the cauliflower stage of inflorescence development on yield and fruit size (pounds/tree) of ‘Hass' avocado trees in Corona, CA.
|Treatment||Total Fruit||Net Increase (%)||Large fruit (213-354 g/fruit)||Net increase (%)|
|GA3||74.7 az||84||34.3 a||128|
|Control||40.6 b||15.0 b|
z Values in a vertical column followed by different letters are significantly different at specified P-values by Duncan's Multiple Range Test at the P-values indicated. (From the work of Salazar-García and Lovatt, 2000).
Table 2. Effect of GA3 (25 g ai/acre) applied at the cauliflower stage of inflorescence development on yield and fruit size as pounds and number of fruit per tree in an alternate bearing ‘Hass' avocado orchard in Irvine, CA.
|Year 1 Yield|
|Treatment||Total Fruit||Net Increase (%)||Valuable Size Fruit (178-325 g/fruit)||Net increase (%)|
|GA3||92.2 az||70||67.9 a||65|
|Control||54.2 b||41.2 b|
|GA3||215 a||76||141 a||70|
|Control||122 b||83 b|
z Values in a vertical column followed by different letters are significantly different at specified P-values by Duncan's Multiple Range Test at the P-values indicated. (From the work of Lovatt and Salazar-García, 2007; Zheng et al., 2011)
Table 3. Effect of GA3 (25 g ai/acre) applied at the cauliflower stage of inflorescence development at on yield and fruit size of ‘Hass' avocado trees in Somis, CA. Percent net increase reflects the benefit of GA3 at 25 g ai/acre relative to the untreated control trees.
|Treatment||Total Fruit||Net Increase (%)||Valuable size fruit (178-325 g/fruit)||Net increase (%)||Large fruit (213-354 g/fruit)||Net increase (%)|
|GA3||408.1 az||10||379.4 a||13||294.1 a||16|
|Control||372.6 b||335.3 b||253.3 b|
z Values in a vertical column followed by different letters are significantly different by Fisher's Protected LSD test at the P-values indicated.
Overall, ground application of GA3 resulted in a net increase of 3,905 lb/acre, with a net increase of 4,851 lb/acre of commercially valuable size fruit (packing carton sizes 60+48+40; 178-325 g/fruit) and a net increase in large fruit (packing carton sizes 48+40+36; 213-354 g/fruit) of 4,488 lb/acre.
Aerial applications were tested on groves located in Pauma Valley and Carpinteria, California. Together, the aerial applications demonstrated that GA3 increased fruit set (fruit retention) by 55 percent into the last week of August and fruit size by 6 percent through mid-August.
Ultimately, Dr. Lovatt's research indicates that use of GA3 could result in substantial increases in net dollar return per acre to the grower due to increase in yield and commercially valuable size fruit. In addition, growers whose avocado groves are not suited to ground applications (groves located on slopes or in high-density formations) can benefit from the efficacy of utilizing aerial applications. In summary, ProGibb LV Plus® is “vital to the California avocado industry to increase grower income per acre to help sustain the California avocado industry.”
N.B. Remember, only well managed trees are going to respond. This will not turn around a poor producing orchard. only potentially increase production on an already good producing orchard. Ben
Two questions and comments came up last week about the use of mulch in orchards. The first is that mulch is two edged. It serves to combat erosion and root rot, but it can also burn. Mulch and wood piled up against tree trunks and near trunks can cause damage to those trunks. A Fillmore grower actually goes through the orchard with a blower to move mulch away from trunks when alerted to fire. On the other hand, irrigated orchards have been shown to be effective at suppressing fire encroaching on homes.
So where to read more about fire? About mulch? Check out some of the blogs from the past.
Mulch and green waste applied to avocado orchards and More
For centuries, the prevailing science has indicated that all of the nitrogen on Earth available to plants comes from the atmosphere. But a study from the University of California, Davis, indicates that more than a quarter comes from Earth's bedrock.
The study, to be published April 6 in the journal Science, found that up to 26 percent of the nitrogen in natural ecosystems is sourced from rocks, with the remaining fraction from the atmosphere.
Before this study, the input of this nitrogen to the global land system was unknown. The discovery could greatly improve climate change projections, which rely on understanding the carbon cycle. This newly identified source of nitrogen could also feed the carbon cycle on land, allowing ecosystems to pull more emissions out of the atmosphere, the authors said.
"Our study shows that nitrogen weathering is a globally significant source of nutrition to soils and ecosystems worldwide," said co-lead author Ben Houlton, a professor in the UC Davis Department of Land, Air and Water Resources and director of the UC Davis Muir Institute. "This runs counter the centuries-long paradigm that has laid the foundation for the environmental sciences. We think that this nitrogen may allow forests and grasslands to sequester more fossil fuel CO2 emissions than previously thought."
WEATHERING IS KEY
Ecosystems need nitrogen and other nutrients to absorb carbon dioxide pollution, and there is a limited amount of it available from plants and soils. If a large amount of nitrogen comes from rocks, it helps explain how natural ecosystems like boreal forests are capable of taking up high levels of carbon dioxide.
But not just any rock can leach nitrogen. Rock nitrogen availability is determined by weathering, which can be physical, such as through tectonic movement, or chemical, such as when minerals react with rainwater.
That's primarily why rock nitrogen weathering varies across regions and landscapes. The study said that large areas of Africa are devoid of nitrogen-rich bedrock while northern latitudes have some of the highest levels of rock nitrogen weathering. Mountainous regions like the Himalayas and Andes are estimated to be significant sources of rock nitrogen weathering, similar to those regions' importance to global weathering rates and climate. Grasslands, tundra, deserts and woodlands also experience sizable rates of rock nitrogen weathering.
GEOLOGY AND CARBON SEQUESTRATION
Mapping nutrient profiles in rocks to their potential for carbon uptake could help drive conservation considerations. Areas with higher levels of rock nitrogen weathering may be able to sequester more carbon.
"Geology might have a huge control over which systems can take up carbon dioxide and which ones don't," Houlton said. "When thinking about carbon sequestration, the geology of the planet can help guide our decisions about what we're conserving."
The work also elucidates the "case of the missing nitrogen." For decades, scientists have recognized that more nitrogen accumulates in soils and plants than can be explained by the atmosphere alone, but they could not pinpoint what was missing.
"We show that the paradox of nitrogen is written in stone," said co-leading author Scott Morford, a UC Davis graduate student at the time of the study. "There's enough nitrogen in the rocks, and it breaks down fast enough to explain the cases where there has been this mysterious gap."
In previous work, the research team analyzed samples of ancient rock collected from the Klamath Mountains of Northern California to find that the rocks and surrounding trees there held large amounts of nitrogen. With the current study, the authors built on that work, analyzing the planet's nitrogen balance, geochemical proxies and building a spatial nitrogen weathering model to assess rock nitrogen availability on a global scale.
The researchers say the work does not hold immediate implications for farmers and gardeners, who greatly rely on nitrogen in natural and synthetic forms to grow food. Past work has indicated that some background nitrate in groundwater can be traced back to rock sources, but further research is needed to better understand how much.
"These results are going to require rewriting the textbooks," said Kendra McLauchlan, program director in the National Science Foundation's Division of Environmental Biology, which co-funded the research. "While there were hints that plants could use rock-derived nitrogen, this discovery shatters the paradigm that the ultimate source of available nitrogen is the atmosphere. Nitrogen is both the most important limiting nutrient on Earth and a dangerous pollutant, so it is important to understand the natural controls on its supply and demand. Humanity currently depends on atmospheric nitrogen to produce enough fertilizer to maintain world food supply. A discovery of this magnitude will open up a new era of research on this essential nutrient."
UC Davis Professor Randy Dahlgren in the Department of Land, Air and Water Resources co-authored the study.
The study was funded by the National Science Foundation's Division of Earth Sciences and its Division of Environmental Biology, as well as the Andrew W. Mellon Foundation.
Photo: The stuff that makes leaves green
- Author: Roger Baldwin, Ryan Meinerz, Gary Witmer and Scott Werner
Baldwin and Meinerz are UC Davis and Witmer and Werner are USDA/APHIA/Wildlife Services-National Wildlife Research Center
Voles are short, stocky rodents that often cause extensive girdling damage to a variety of tree and vine crops throughout California. Vole management is often quite challenging given how numerous they can be in a given area. In more recent years, effective management has often relied on some combination of vegetation removal, exclusion using trunk protectors, and rodenticide application. Vegetation removal is a great tool for reducing numbers in a field, but doesn't always eliminate all problems in an area. Plus, vole population size tends to ebb and flow from low to high densities; when densities are high, vegetation removal is often insufficient to reduce girdling damage.
Exclusion through the use of trunk protectors can be a good way to reduce girdling damage as well. However, trunk protectors should be buried at least 6 inches below ground to keep voles from tunneling underneath the protectors. This substantially increases the amount of labor required to protect trees and vines. Ultimately, this approach is only cost effective if high levels of damage are anticipated.
Rodenticide applications are also frequently used to knock down vole populations. However, rodenticide applications are generally not allowable within an orchard or vineyard during the growing season, thereby eliminating the use of one of the most effective vole management tools when it is most needed. Clearly there is room for a new tool to be added to the proverbial IPM toolbox when it comes to managing voles in orchard and vine crops.
Chemical repellents are one such tool that could be considered. Historically, repellents have not proven overly effective for field application against voles. However, recent laboratory testing of anthraquinone indicated that even low concentrations of this chemical were effective at reducing grain consumption by voles. Furthermore, anthraquinone has proven effective as a bird repellent. Anthraquinone is a post-ingestive product that causes animals that consume the product to become ill, thereby making it less likely that the animal will consume the product again during a subsequent feeding event. This kind of repellent is ideally suited for trunk application given that the repellent can easily be applied to the portion likely to be consumed by the vole. If effective, minimal girdling damage should be observed. A repellent application also has the added advantage in that it can easily be paired with vegetation management to hopefully further reduce girdling damage when compared to using either one of these approaches alone. Therefore, we set up a study to test the potential impact that a combination of vegetation management and anthraquinone applications would have on girdling damage by voles to young citrus trees. We also tested the longevity of anthraquinone to determine if long-term repellency following field application was likely. We tested this impact during both spring (characterized by a cool-wet weather pattern) and summer (characterized by a hot-dry weather pattern) seasons to determine if weather impacted potential girdling damage.
We found that anthraquinone was in fact highly repellent following trunk application, with a >90% reduction in girdling damage observed following application regardless of the season when it was applied. Anthraquinone exhibited substantial longevity, with no increase in girdling damage observed for the entire summer (5 weeks) and spring (6 weeks) sampling periods. This clearly indicates substantial repellency for anthraquinone applications, with repellency to last for at least two months, and likely for much longer given that we observed no upward trend at all in girdling damage at the end of our study period.
When combined with anthraquinone treatments, the removal of vegetation completely eliminated all girdling damage during summer. However, we did not observe this same collective impact during spring. That said, the inclusion of vegetation management with anthraquinone applications is likely warranted given our understanding of the need for multiple management strategies to maintain the long-term effectiveness of rodent management programs.
These results clearly indicate effective repellency of voles following anthraquinone applications, but at this time, anthraquinone is not registered for use against any mammalian species. We are hoping to gauge the interest of growers for the registration of this repellent against voles in orchard and vine crops. This is where we need your help. We have developed a very short survey (will take less than 3 minutes to complete) to gauge this interest. Please take this very quick survey to assist in this effort:
The California Avocado Commission is pleased to announce the availability of ProGibb LV Plus Plant Growth Regulator Solution (gibberellic acid) for use on avocados in California under a Special Local Needs (SLN) registration effective March 27, 2018. ProGibb has been shown to effectively increase fruit size and set when applied at the cauliflower stage of bloom.
ProGibb LV Plus can be applied from the ground or by air. Ground applications should be made by mixing 12.5 fluid ounces of product in 100 gallons of water per acre. Aerial applications should be made by mixing 12.5 fluid ounces of product in 75 gallons of water per acre. Only one (1) application is allowed per year.
The restricted entry interval (REI) is 4 hours, and the preharvest interval (PHI) is 0 days, so ProGibb LV Plus can be used with minimal disruption to harvesting and other grove management activities.
- A copy of the SLN Label must be in the possession of the user at the time of application.
- The signature of the County Agricultural Commissioner or their designee must be obtained prior to the use of ProGibb LV Plus.
- This SLN is only valid for the ProGibb LV Plus product manufactured by Valent BioSciences Corporation. Generic gibberellic acid products may not be used under this SLN.
The California Avocado Commission wishes to thank Dr. Carol Lovatt, University of California Riverside, for her many years of dedicated research that made this registration possible. We also thank the many growers, PCAs, and pesticide applicators who participated in the research trials.
If you have any questions about this SLN registration and the use of ProGibb LV Plus, please consult with your local PCA or you may contact Tim Spann at email@example.com.
Photo: Cauliflower stage of flowerr/span>