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.

UAV-based Remote Sensing Can Help

      Avocado Growers by

                Detecting Asymptomatic Pathogen

GAINESVILLE, Fla. — Remote imaging can effectively detect a pathogen that endangers the $100 million-a-year Florida avocado industry – even before the trees show symptoms — University of Florida scientists say.

Yiannis Ampatzidis, an assistant professor of agricultural and biological engineering at the UF Institute of Food and Agricultural Sciences, led recently published research that shows that multispectral cameras can detect laurel wilt on avocado trees. The approach costs less than manually trying to detect the laurel wilt pathogen, Ampatzidis said, though UF/IFAS researchers don't know yet the cost differential.

Avocados provide an estimated $100 million-a-year economic benefit to the state's economy, according to UF/IFAS research. California grows most of the nation's avocados, but Florida is the second-leading producer. About 95 percent of Florida' avocados are grown in South Florida, particularly in Miami-Dade County. So UF/IFAS researchers first infected avocado trees with laurel wilt at the UF/IFAS Tropical Research and Education Center in Homestead, Florida.

Then they brought those trees to the UF/IFAS Citrus Research and Education Center in Lake Alfred, Florida, where Jaafar Abdulridha, a postdoctoral researcher for Ampatzidis, tested if the remote-sensing techniques would discern the laurel wilt pathogen. At the Citrus REC, UF/IFAS researchers identified wavelengths that they can use to detect laurel wilt early in avocados.

Multispectral cameras can capture data within specific wavelengths across the electromagnetic spectrum, said Ampatzidis, who specializes in precision agriculture. Humans can only see very small areas of the spectrum.

“In general, growers need to scout their field and visually detect infected plants,” said Ampatzidis, a faculty member at the UF/IFAS Southwest Florida Research and Education Center in Immokalee, Florida. “It is very time-consuming, labor-intensive and costly. And of course, they can only detect diseases based on their symptoms.”

“Using different filters, we can separate wavelengths,” he said. “So, these multispectral cameras are sensitive to particular wavelengths.”

The proposed system could detect diseases in asymptomatic stages, thus telling growers earlier that their trees are infected, he said. An unmanned aerial vehicle – or drone — with a multispectral camera can cost between $3,000 and $8,000, Ampatzidis said.

The new study is published in the journal Computers and Electronics in Agriculture.

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By: Brad Buck, 352-294-3303, bradbuck@ufl.edu

The mission of the University of Florida Institute of Food and Agricultural Sciences is to develop knowledge relevant to agricultural, human and natural resources and to make that knowledge available to sustain and enhance the quality of human life. With more than a dozen research facilities, 67 county Extension offices, and award-winning students and faculty in the UF College of Agricultural and Life Sciences, UF/IFAS works to bring science-based solutions to the state's agricultural and natural resources industries, and all Florida residents. Visit the UF/IFAS web site at ifas.ufl.edu and follow us on social media at @UF_IFAS.

Avocados in some parts of coastal California have been blooming.  Some of them got hit by the cold weather in the first part of February.   In the coldest areas there was a little bit of new leaf damage, but this has been minimal.

Some browning of some flowers and stems (pedicels - the little stalks the connect the flowers to the larger raceme/panicle) may have occurred, but I haven't heard of major flower damage.

It's early days for flowering, though, and most ‘Hass' trees are not very far along, but seem like they area about to burst.  A recent visit on a 40 acre farm in Saticoy had trees in a whole range of stages, some with no flowers pushing, some with panicles just starting to open individual flowers and many trees on their north sides' completely quiet.    Many are still just pushing into the cauliflower stage,

which is the ideal time is for applying Pro-Gibb to improve fruit set in healthy orchards. 

Application time is when 50% of the trees in the block have 50% of their bloom in the cauliflower stage.  This is a judgment call when there can be such huge variation in bloom across and orchard.  It's going to be a best estimate call for when to do the application.  As usual with a new technology/practice don't apply to the whole orchard so that you can see whether the application is warranted.

For a more detailed discussion of gibb application, read Carol Lovatt's article:

"Trees should be firmly staked at planting"

        MYTH!!!!!!!!!!!!!!! Read on:

Chalker-Scott, L. , Extension Specialist And Associate Professor, Washington State University
Downer, A.J., Farm Advisor, University of California

Nursery-grown shade trees are often rigidly staked to prevent blowdown and damage during cultivation. In some cases, trees are pruned to a long, untapered standard with a bushy top that requires a tight stake to hold it up. Nurseries often remove side branches from the young trunk and while this creates the illusion of a small tree, the practice actually inhibits the development of taper in the trunk (Harris, 1984; Neel and Harris, 1971). Trees without taper will not stand without staking. Poor culture of ornamental trees in nurseries necessitates staking once trees are planted into landscapes because they do not have the structural development in their trunks to stand on their own. Due to these cultivation errors, landscape installers frequently keep the nursery stake and add more stakes to firmly secure the tree in place and further prevent its movement in the landscape.

Staking takes three basic forms: rigid staking, guying, and anchoring. All methods of staking reduce development of taper, increase height growth, and decrease caliper of the developing tree relative to unstaked trees (Figure 7). Moreover, improper staking can result in increased tree breakage either during the staking period or after staking is removed (Figure 8a-b) (Thacker et al., 2018).

Decades ago, researchers discovered that movement of the trunk and branches is necessary for the development of trunk taper (Neel and Harris, 1971). Trees grown in a growth chamber without movement did not develop taper and instead grew taller, while trees in an identical chamber that were hand shaken each day developed significant taper and remained shorter.

Until trees are established in landscapes they may require some staking. In areas of high wind, guying (which involves cables staked to the ground) gives the greatest protection against main stem breakage or blowover (Alvey et al., 2009). Whatever system is used, any such hardware should be removed as soon as the tree can stand on its own:

• The traditional two stakes and ties system is the least harmful to trees staked in landscapes.
• Staking should be low and loose to allow trunk taper to develop naturally.
• Remove all staking material as soon as possible.

If a tree is not established after a year of staking, it is unlikely to ever establish

Read on:

https://www.nacaa.com/journal/index.php?jid=885&fbclid=IwAR3fS2iKo8ibifQEDPUrG6UlcB8n-yUgOe6xx1y56MeAcLhP6ZoUkQbUQNg