- Author: Ben Faber
Water Quality Impacts on California Avocado –
A Collaborative Approach
Sat Darshan S. Khalsa1 and Ben Faber2
1Department of Plant Sciences, UC Davis
2Cooperative Extension Ventura County, UCANR
Avocado consumption continues to grow both in the U.S. and around the globe. Greater demand creates an opportunity for growers to supply an expanding market with quality California fruit. More intensive production increases the need for attention to tree health, crop protection and irrigation practices. Many avocado root rot diseases are related to how growers manage water, and given the salt sensitivity of avocado and limited selection of salt-resistant rootstocks, water quality is an inherent driver of avocado productivity and quality.
In the California avocado-growing regions of the Central and South coast, water quality can be highly variable. Groves can rely on a combination of surface and groundwater yet, water high in total dissolved solids, pH and salts such as sodium and chloride, can be common place. Furthermore, water quality properties are subject to change as California faces more weather extremes and shifting water demand. As a result, avocado growers need to continue to be conscientious of how local and regional water quality conditions impact their groves.
A comprehensive understanding of how water quality impacts avocado tree health and fruit quality is still limited. The consensus is irrigation with poor quality water reduces crop productivity yet, the extent to which crop loss is linked to water quality and specific practices to mitigate the risk is not entirely clear. The clonal rootstocks ‘Dusa', ‘Toro Canyon' and ‘Duke 7' have some salt tolerance, but are still sensitive to salts. Even less information is available on the potential impacts of water quality on fruit quality, including both nutritional value and postharvest storage.
A collaborative approach to problem-solving creates an opportunity for growers to participate in research and to generate regional and site specific solutions. The phases of this project include 1) identify the range of water quality conditions in California avocado-growing regions; 2) build a network of ‘focus sites' identified by grower participants using specific grove characteristics and; 3) monitor field indicators to quantify impacts of water quality on tree health and fruit quality. Results will be shared in aggregate to maintain the privacy of participants and also, allow growers to compare their focus site with a wider population.
If you are interested in learning more about this collaborative water quality project, please contact Dr. Khalsa at sdskhalsa@ucdavis.edu or sign up for a follow-up conversation using this webform (http://madmimi.com/signups/fbeac7dee8264fac90ab8a9b6f0c65ff/join).
Sat Darshan Khalsa is an Assistant Project Scientist in the Department of Plant Sciences at UC Davis (http://www.plantsciences.ucdavis.edu/people/sat-darshan-khalsa) and Ben Faber is the UCANR Soils/Water/Subtropical Crops Advisor for Ventura and Santa Barbara Counties (http://ceventura.ucanr.edu/Staff/?facultyid=638).
Photo: These aren't avocados.
- Author: Ben Faber
If you hang around an orchard long enough something unusual will show up, especially when seasons change and there's more rain than usual and it's cold, but not so cold that it freezes and it's prolonged. So out of San Diego comes a request for an identification of a brown bump on avocado stems. It's a brown aphid. Is it something of concern? Likely not. Over the years there have been reports of several aphids on avocado. Check out Walter Ebeling's "Subtropical Fruit Pests" at Avocadosource.com:
http://www.avocadosource.com/papers/research_articles/ebelingwalter1959b.pdf
These things come and go, and they don't do any damage because once the biocontrol bugs get going, they are fresh meat for them.
- Author: Ben Faber
This is an intriguing article that popped up about how to improve blueberry production in alkaline soils. High pH soils are a major issues for many of our tree crops along the coast. pH is what controls the availability of most plant nutrients and what bacteria and fungi grow in the soil, creating the biosphere. So can growing a grass cover crop in our orchards improve lemon and avocado production?
A lawn is better than fertilizer growing healthy blueberries
Intercropping with grasses is an effective and sustainable alternative to chemical treatments for maximizing blueberry yield and antioxidant content in limey soils.
Blueberries are prone to iron deficiency - and correcting it increases their health-enhancing antioxidant content, researchers have discovered.
Published in Frontiers in Plant Science, their study shows that growing grasses alongside blueberry plants corrects signs of iron deficiency, with associated improvements in berry quantity and quality. The effects are comparable to those seen following standard chemical treatment - providing a simpler, safer, cheaper and more sustainable strategy for blueberry farming on sub-optimal soils.
What do superfruits eat?
All soils are rich in iron, but nearly all of it is insoluble.
"Most plants get enough iron by secreting chemicals that make it more soluble," explains senior study author Dr José Covarrubias, Assistant Professor of Agriculture Sciences at the University of Chile. "These iron 'chelators' can be released directly from the roots, or from microbes that grow among them, and allow the iron to be absorbed."
"Blueberries, however, lack these adaptations because they evolved in uncommonly wet, acid conditions which dissolve the iron for them."
As a result, most of the world's relatively dry or alkaline ('limey') cropland is unsuitable for optimal blueberry growth.
"Iron is essential for the formation and function of plant molecules like chlorophyll that allow them to use energy," Covarrubias continues. "That's why iron deficiency shows up as yellowing leaves - and drastically reduces plant growth and yield.
"And in blueberries, iron-dependent enzymes also produce the 'superfruit' antioxidants responsible for their celebrated blue skin and health-enhancing effects."
Strong blueberries must pump iron - but at what cost?
There are two approaches to correcting iron deficiency in blueberries: acidify the soil, or add synthetic iron chelators. Each has its drawbacks, says Covarrubias.
"The commonest industrial approach is soil acidification using sulfur, which is gradually converted by soil bacteria into sulfuric acid. The effects are slow and difficult to adjust - and in waterlogged soils, hydrogen sulfide might accumulate and inhibit root growth.
"Acids can also be added directly via irrigation systems for more rapid acidification - but these are hazardous to farmers, kill beneficial soil microbes, and generate carbon dioxide emissions.
"A commoner strategy among growers is application of iron bound to synthetic chelators - often sold as 'ericaceous fertilizer' - but these are very expensive and leach potentially toxic chemicals into the water table."
A cheaper, safer alternative is needed for efficient large-scale blueberry production. Thankfully, one already exists.
"Grasses - which are well-adapted to poor soils - can provide a sustainable, natural source of iron chelators via their roots when grown alongside fruiting plants. Intercropping with grass species has been shown to improve plant growth and fruit yield in olives, grapes, citrus varieties - and most recently, in blueberries."
A grassroots approach to sustainable blueberry farming
Now, Covarrubias and colleagues have brought intercropping a step closer to the mainstream of blueberry cultivation.
For the first time, they measured the effects of different methods of iron chelation on antioxidant content and other fruit qualities in blueberries.
"In an orchard of 'Emerald' blueberry bushes cultivated in alkaline (pH 8) soil, we compared the effects of five different iron chelation treatments: a 'gold-standard' synthetic iron chelator (Fe-EDDHA), intercropping with grass (common meadow grass or red fescue), cow's blood (Fe-heme), or no treatment (control)."
"We found the association with grasses increased not only the total weight and number of blueberries per plant, but also the concentration of anthocyanins and other antioxidant compounds in their skins, compared to control. The effect sizes were comparable with the proven synthetic chelator Fe-EDDHA, whereas applications of Fe-heme from cow's blood - a fertilizer commonly used in home gardens - had no significant effect."
The beneficial effects paralleled improvement in the plants' iron status (leaf color), which was also comparable between the grass-associated and the Fe-EDDHA-treated plants. None of the treatments had a significant effect on average berry weight
Turf is ready to roll out for healthier blueberries
A potential limitation of intercropping observed in the study was a decrease in berry firmness, since firmer berries are favored by consumers.
"The association with grasses decreased berry firmness compared with control plants, whereas the berries collected from plants treated with Fe-EDDHA reached intermediate values.
"However chemical analysis showed a non-significant trend towards increased ripeness in the berries collected from the intercropped plants, which could account for this small difference."
Intercropped plants also required an additional water supply to maintain a similar soil moisture to other treatments, but plant management was otherwise straightforward and the same across groups. The grasses were kept cropped between 5 and 15cm - a typical range for an attractive mown lawn.
"Our findings validate intercropping with grasses as a simple, effective, sustainable alternative to standard iron correction strategies in blueberries," concludes Covarrubias. "Both commercial and private growers can put this strategy to use right away to boost their blueberry crop and antioxidant content."
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Please link to the original research article in your reporting: https://www.frontiersin.org/articles/10.3389/fpls.2019.00255/full
Frontiers is an award-winning Open Science platform and leading Open Access scholarly publisher. Our mission is to make research results openly available to the world, thereby accelerating scientific and technological innovation, societal progress and economic growth. We empower scientists with innovative Open Science solutions that radically improve how science is published, evaluated and disseminated to researchers, innovators and the public. Access to research results and data is open, free and customized through Internet Technology, thereby enabling rapid solutions to the critical challenges we face as humanity. For more information, visit http://www.frontiersin.org and follow @FrontiersIn on Twitter.
- Author: Ben Faber
Next up on Ag Experts Talking is Laurel Wilt Disease which is causing major damage in the native tree populations of the south east United States and the avocado groves in particular. Learn what is being done there and what the potential threat is to California avocados.
What Are the UC Ag Experts Talking About?
What is involved in the webinars?
A series of 1 hour webinars, designed for growers and Pest Control Advisors, will highlight various pest management and horticultural topics for citrus and avocados. During each session, a UC Expert on the subject will make a presentation and entertain write-in questions via chat during and/or after the presentation. As we develop this program, we may expand to other crops.
Topics: pests and diseases of citrus, avocado and other crops
What are the topics and how do I register?
Laurel Wilt (March 20, 2019 from 3-4 pm)
Dr. Monique J. Rivera will present current knowledge of the laurel wilt, the biology and ecology of its vector - Ambrosia beetles, current known location of the disease in the US, Identifying the disease, and the laurel wilt disease prevention in California.Dr. Monique J. Rivera will present current knowledge of the laurel wilt, its biology and spreading. One DPR CE unit (other) and one CCA CE unit (IPM) are pending.
Register:
https://ucanr.edu/sites/ucexpertstalk/?calitem=439527&g=103975
Management of Glyphosate-Resistant Weeds in Orchard Crops (April 24, 2019 from 3-4pm)
Dr. Brad Hanson, cooperative extension specialist, will discuss what is herbicide resistance, current state of resistant weeds in CA permanent crops, identification and lifecycle of key glyphosate-resistant weeds, selection pressure for resistant biotypes and species, herbicide modes of action, and examples of herbicide programs for orchard crops. One DPR CE unit (other) and one CCA CE unit (IPM) are pending.
Register:
https://ucanr.edu/sites/ucexpertstalk/?calitem=439496&g=103975
Are there Continuing Education units?
When the subject discusses pest or disease management, continuing education units will be requested from DPR (1 unit per session). Participants will pre-register, participate in the webinar and be awarded the unit. The sessions will be recorded and hosted on this web site for future study. However, continuing education units will be awarded only to the participants who attend the live version of the webinar.
Who is involved?
This webinar series is brought to you by Ben Faber (UC ANR Ventura Advisor) and Dr. Beth Grafton-Cardwell (Depart of Entomology UC Riverside Extension Specialist) with the technical support of Petr Kosina (UC IPM Contect Development Supervisor) and Cheryl Reynolds (UC IPM Interactive Learning Developer).
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- Author: Ben Faber
So a question comes in about a problem with a backyard avocado tree. And it would seem the first question would be about the overgrowth happening at the base of the trunk. This a ‘Fuerte' avocado that is grafted on a seedling avocado rootstock. It's not unusual to see an overgrowth, but this is the most extreme example I have ever seen. So it's basically an incompatibility between the graft and the rootstock. In many cases this is no big problem and trees can live a long time, as this tree has.
But the homeowner wasn't asking about the unusual growth at the base, but the canker that had appeared in the center of the trunk near the base.
This has the classic white sugar exudate that occurs with a wound of any kind in avocado. The sugary sap that contains the unusual mannoheptulose 7-carbon sugar characteristic of the laurel family to which avocado belongs will ooze out of the wound and result in a white crust (Read more about this sugar at: https://www.sciencedirect.com/science/article/pii/S0254629911001372 ).
Anyway, so this backyard tree is in an area that is getting 10 minutes of lawn watering a day. Lawns and avocados don't get along. And avocados don't get along with short, shallow irrigation that result in salt accumulating in the root zone. Which is what has happened here. Salt stress and the result is an infection of bacterial canker (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=7920 ).
It's not fatal in an old tree like this, but it can predispose the tree to root rot. And that's not something that is easy to treat in backyard settings.