- Author: Ben Faber
Advances in Citrus Water Management Virtual Workshop
September 9-10, 2021
9AM-12PM PT
REGISTER HERE
Virtual Workshop via Zoom. Zoom information will be sent to registrants closer to the event.
Objective: Join UC Irrigation Specialists Daniele Zaccaria and Khaled Bali, and other University of California experts in this 2-day on-line Workshop to learn about the latest research and advances in Citrus irrigation. Topics include: Citrus water relations, evapotranspiration and crop coefficients, soil-water budgeting, soil characterization and mapping, tree water status, remote sensing, micro-irrigation systems' evaluation, interpreting results of water analysis, and strategies for Citrus irrigation management under limited water supplies. A set of irrigation-related methods, technologies, and products to help schedule irrigation will also be presented during the Workshop. Registration includes participation to the two sessions and access to the recorded workshop presentations. You can view a current event agenda here.
Intended audience: citrus growers and farm managers, representatives from the citrus production industry, irrigation consultants and practitioners, CCAs, CPAs, water resource managers, water conservation districts' personnel, irrigation districts' managers, extension specialists and advisors, professional researchers, university students, and representatives from state agencies.
Contacts for More Information
Logistics/Registration: ANR Program Support, 530-750-1361.
Program: Daniele Zaccaria and Khaled Bali
Henry Herrera, Forester, California Department of Forestry and Fire Protection (CAL FIRE)
Gary Bender, Subtropical Horticulture Advisor, Emeritus, San Diego County
This is a reposting of a blog from 2015 that is still pertinent today and for the foreseeable future.
Vegetation Weed Management
Vegetation weed management is something CAL FIRE feels strongly about, especially during times of drought. CAL FIRE interprets this type of weed management as a fuel reduction or fuel modification practice which helps growers create defensible space around their habitable structures or groves. Defensible space is a buffer between property (i.e. homes, groves, infrastructure) and plants (i.e. brush, trees, etc.) or other items surrounding the property to be protected that could catch fire and act as fuel.
Defensible space is needed to slow the spread of a wildfire and improves the safety of firefighters defending properties. Defensible space reduces the fire risk and creates space that firefighters can use as a tool to work safely and suppress a wildfire and to defend a structure or other property in the event of a wildfire. Fuel modification/reduction projects include defensible space around structures, fuelbreaks along roads and groves, ridge tops, or around property lines and other fire fuel reduction activities that lessen the risk of wildfires to communities. Fuel reduction projects usually remove cut vegetation from the site either through burning or haul-away methods. Fuel modification projects usually leave the cut vegetation on site in the form of wood chips or scattered material. These types of projects break up the lateral and horizontal vegetative continuity which reduced rates of fire spread, fire intensity, and flame heights which increase firefighter's chances of suppressing fires.
Prunings piled in draws within or around the groves can also be particularly damaging because they are dried vegetation which pose an increased fire danger due to the fact that piles of vegetation can easily ignite and smolder for a long time creating a challenge to firefighters. Vegetation that is piled in draws or other waterways can also obstruct water flow during rain events which could lead to erosion and flooding.
How to Keep our Growers and Groves Safe
Preventative Measures:
These preventive measures can be suggested for groves in areas of high fire hazard are often counter to other measures which might reduce erosion or improve root disease control, so a balance should be strived for (Goodall 1965):
1. Remove all combustible material from around the trunks of the trees for a distance of two to three feet.
2. Prune off low-lying limbs, those that are low enough to accumulate more than the normal inch or so of leaf mulch.
3. Remove from the orchard all broken limbs, deadwood and other combustible debris.
4. Clear brush, trees and other heavy vegetation away from edge of orchard for a distance of at least 50 feet.
5. Do not pile brush or other combustible material in draws or canyons, or around the edges of groves.
6. Apply sprinkler water for as long a period in advance of the fire as possible so as to have everything wet. Water during the fire would obviously be desirable but often is lacking because of lack of pressure or speed of the movement of the fire.
7. Use steel pipe and risers for above ground sprinkler systems.
Growers can also look for other tips on preventive measures on the Cal Fire website: http://calfire.ca.gov/fire_prevention/fire_prevention.php.
After a Fire
It is nearly impossible to determine the extent of damage to the wood of the tree immediately after the fire. The most critical part of the tree is the main trunk. The bark from just above the ground to about two feet high can become hot enough to kill the cambium, the growth layer between the bark and wood. When the cambium is killed, the tree is girdled and will die (Goodall 1965). Suckers will eventually grow from below the graft union of these trees; these suckers can then be grafted to an appropriate variety. However, many trees in the grove may still be alive internally because there was a quick burn through the grove, or the leaves merely died from heat generated by burning surrounding trees, vegetation and mulch (Bender 2012).
According to Bender (2012), fire damaged trees that have leaves that are completely brown do not use water, but there may be trees that have escaped the fire in the irrigation block and these need to be irrigated as soon as possible. The first thing to do is to repair the irrigation system. Risers, sprinklers, pressure regulators and poly-hose on the ground are probably melted and should be replaced as soon as possible. PVC pipe that is buried underground is usually fine, depending on its depth and fire intensity. If part of the trees in the irrigation block are alive and partly damaged, it would probably be best to roll out poly-hose onto the damaged trees and set up a separate irrigation block. As the trees recover and start using water, you can eventually go back to the permanent system.
Trees that are heavily damaged do not use as much water (therefore transpiration is reduced significantly), but their feeder roots need to be watered and short irrigations should occur to replace water evaporating off of the soil surface. Start with a one hour irrigation and monitor the soil closely, irrigating too heavily could lead to the onset of root rot. Do not irrigate damaged trees on its original schedule; a ten hour irrigation will not “force” the trees to grow back sooner, and roots could be easily damaged by lack of oxygen in the lower soil profiles due to water accumulating and the soil becoming saturated.
Every fire is different, so experiences vary. It may take several months to be able to observe whether the bark is killed all the way to the cambium or not. Thus, we recommend against pruning until new growth appears to indicate where the wood is alive. According to Bender (2012), an alternative method which is rather unique to the avocado industry, the burned trees can all be stumped immediately and allowed to re-grow. “Stumping” is a normal practice in the industry when avocado trees have reached such heights that fruit is high off the ground and picking becomes difficult. In many of the groves that were burned, stumping was probably needed anyway; therefore after a burn stumping would be a reasonable alternative for many growers.
Fire damaged trees should be whitewashed on the south side of the limbs. Goodall (1965) also suggests to save expenses, fertilizer and pest control can be postponed for a year or so.
According to Bender (2012), if the goal of the grower is to bring trees back into production as soon as possible, the avocado tree will usually recover production faster if the grower is patient and prunes only the dead wood three months after the fire. Unfortunately, this practice creates a permanent problem in the grove as far as irrigation scheduling and application. Mixing full-grown trees (untouched by the fire) with partially pruned trees (and stumped trees) in an irrigation block means that some trees will be over-watered, or under-watered, depending on their size. Adjustments can be made in the sprinkler sizes, but generally this is an undesirable cultural practice due to every tree needing a different rate of irrigation and can this can also add to labor and equipment costs.
If the goal is to reduce the size of all trees in the irrigation block to a manageable size, then stumping the block immediately after the fire is the best solution. Trees will be out of production for two years and have about 50% production in the third year, and some re-grafting may have to be done, but fertilizing and watering properly is manageable.
A third option could be to scaffold all trees in an irrigation block to 12' in height. This would get rid of a lot of dead wood immediately, and might allow the trees to come back in production faster than the stumping the trees.
It is helpful for growers to know the value, for insurance purposes, of trees that are lost due to fire. Determining the value of a tree in an orchard is not a simple matter because one must take into account the income lost if the tree had been producing, as well as the costs of planting and maintaining the new tree. Also, the income from the new tree, once it comes into bearing, helps to defray the costs involved in bringing the tree to maturity. Examples can be seen here at the UCCE website: http://ceventura.ucanr.edu/Agricultural_Threats/Fire_Information/. Assessing tree loss can be calculated at the UC DAvis Ag Econoimics website: https://coststudies.ucdavis.edu/en/tree-vine-loss/
Record-low rainfall, extreme heat and a statewide drought has caused a significant increase in wildfires and a need for Californians to participate in fire-prevention tactics, including growers. According to CAL FIRE, in order to prevent wildfires and property damage, homeowners are asked to maintain “defensible space” around their house and groves year round and not use powered equipment outdoors when it's hot, dry or windy. Wildfire prevention such as defensible space, keeping properties cleared of dried vegetation, and public education is the best long term solution.
Photo 1: An inmate firefighter crew battles a fire in an avocado grove outside Fallbrook, California, May 14, 2014. Photo: Sandy Huffaker
Photo 2: Low intensity fire damage on avocados. Photo: U.S. Today
Photo 3: A CAL FIRE inmate crew fighting a wildfire in an avocado grove, May 2014. Photo: Sandy Huffaker
Work Cited
Bender, Gary. 2012. Recovery from Fire Damage in Avocado Groves. UCCE San Diego Website: cesandiego.ucanr.edu/files/54279.doc. [Accessed June 16, 2015].
Goodall, G. E. Avocados and the Coyote Fire. California Avocado Society 1965 Yearbook 49: 81-83.
Ventura Co UCCE publication. Calculate Cost of Fire Damage to Avocado and Citrus Trees. Growing Avocados in Ventura County Reference Book. UCCE Ventura
A great idea from Ed McFadden of Philmore
You can always do something to prevent or correct the Big 4 that seem to strike avocados on a regular basis somewhere in California. Avocados in the back country are right up against areas that can burn easily. A fast fire can send embers into an orchard which can burn through the thick leaves in a slow burn. If it gets up against leaves piled up against the trunk, it can girdle the tree, killing it. The slow burn can continue through the orchard torching the irrigation lines. With a small fire break where the leaves are removed in a small alley, the burn can be slowed or stopped.
Leaves are great for erosion control, for nutrient cycling and disease control, but if they mean increasing potential for fire spread, it's a good idea to remove a little of it. Ed has found that a backpack blower can rapidly remove leaves from around the base of trees and create a narrow fire break that can reduce fire damage to trees. He now clears a 6-8' diameter pattern around the trunk.
Avocado orchards are notable for their ability to actually reduce fire hazard and slow major fires as has been shown in fires in San Diego, Ventura and Santa Barbara. This is partly due to running sprinklers during wild fire. But tree loss can still occur, especially when electricity goes down and pumps can't run.
Little rain this year or too much rain this year can always pose a hazard to avocado orchards. This sure seems like a good idea to me. And maybe it's time to start thinking about fire season now.
Photos: Cleared alley and trunk.
And After the Fire:
Avocado Orchards in Fire Season - Topics in Subtropics - ANR Blogs (ucanr.edu)
- Author: Ben Faber
Burrowing Rodents: Developing a
Management Plan
for Organic Agriculture in CA
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Tomomi Okubo
tomomi.okubo@oist.jp
Office: 81-989-823-447
- Citrus fruits from the mandarin family have important commercial value but how their diversity arose has been something of a mystery
- Researchers analyzed the genomes of the East Asian varieties and found a second center of diversity in the Ryukyu Islands along with the previously known center in the mountains of southern China
- They discovered a new citrus species native to Okinawa that arose about two million years ago when the Ryukyu archipelago became disconnected from mainland Asia
- Other citrus from Okinawa and mainland Japan, including shiikuwasha and tachibana, are hybrids of this newly discovered wild species with different mainland Asian varieties
- This research may have commercial implications and opens the potential to create additional hybrids with favorable traits
Citrus fruits from the mandarin family are popular throughout the world for their tasty and healthy characteristics. Within Japan, the tiny shiikuwasha and the ornamental tachibana are of special cultural and historical importance. However, the origin of these two varieties, and other East Asian citrus, was always something of a mystery, until now.
In a new study, published in Nature Communications, scientists from the Okinawa Institute of Science and Technology Graduate University (OIST), and collaborators from other institutes, analyzed 69 genomes from the East Asian mandarin family, alongside their mainland Asian relatives, to reveal a far-ranging story of isolation, long-distance travel, and hybridization.
The story starts in the Hunan Province of southern China, which is the center of wild mandarin diversity and the genetic source of most well-known mandarins. When the scientists re-analyzed previously published genomic data, they unexpectedly found that wild mandarins of this mountainous region are split into two subspecies.
"We found that one of these mandarin subspecies can produce offspring that are genetically identical to the mother," said Dr. Guohong Albert Wu, a research collaborator at the Lawrence Berkeley National Laboratory in California. "Like many other plants, wild citrus typically reproduces when the pollen of the father combines with the egg of the mother, mixing the genes from both parents in the seed. But we found a subspecies of wild mandarins from Mangshan, in southern China, where the seed contains an identical copy of the mother's DNA without any input from a father. So, the seed grows to be a clone of the mother tree."
Back in Okinawa, the researchers looked more carefully at a strange shiikuwasha-like citrus that produces small, acidic fruit and had been ignored by local farmers since it has little commercial value. To their surprise, they found that this strange citrus represented a previously undescribed species, which they named the Ryukyu mandarin or, more formally, Citrus ryukyuensis. And in contrast to the well-known shiikuwasha, which reproduces clonally (like the subspecies in Mangshan), the new species always reproduces sexually.
Remarkably, the researchers found that all shiikuwasha are hybrids of a very specific type--one parent is from the local Ryukyuan species and the other, from mainland Asia. Surprisingly, all shiikuwasha have the same mainland mandarin parent, meaning that all shiikuwasha are half-siblings.
They concluded that tens of thousands of years ago a mainland Asian mandarin was transported, either by people or by natural methods, to the land that would become the Ryukyu Islands. There it mated with the native Ryukyu citrus. The researchers traced the ancestry of this mainland Asian mandarin back to Mangshan, where it acquired its ability to reproduce asexually. This ability was passed on to its children.
Thus, all the shiikuwasha varieties found in Okinawa's markets today are descended from this mating, and reproduce asexually, allowing stable varieties like golden shiikuwasha to be propagated from generation to generation.
And what of tachibana and the other East Asian mandarin variations?
"They're all hybrids!" explained Dr. Chikatoshi Sugimoto, Postdoctoral Scholar in OIST's Molecular Genetics Unit. "The tachibana lineage also seems to have descended from the newly described Ryukyu species and another mandarin from China, but its birthplace was probably what is now mainland Japan."
Once they saw the genetic pattern in shiikuwasha and tachibana, the researchers also recognized another half-sibling family comprising various traditional Ryukyuan types--oto, kabuchii, tarogayo, and other unnamed citrus. This family, which the researchers called 'yukunibu' (sour citrus in the native Okinawan language), is much younger than shiikuwasha and tachibana. It arose when the famous kunenbo--also the father of satsuma mandarins--hybridized with the native Ryukyu mandarin. Kunenbo was brought to Okinawa from Indochina around 4-500 years ago by maritime trade. Like the mainland parents of shiikuwasha and tachibana, it was also able to clone itself by seeds, due to its distant Mangshan ancestry, and it passed this trait on to its children.
"It's fascinating to puzzle out the story of mandarin diversification and its relationship to the biogeography of the region," concluded Prof. Dan Rokhsar, Principal Investigator of OIST's Molecular Genetics Unit. "But it also could have commercial value. What other possibly hybrid types are there? Could we create new hybrids that are more resilient to disease or drought, or have other desirable characteristics? By looking into the past, we can create all sorts of possibilities for the future."
And the whole article: https://www.nature.com/articles/s41467-021-24653-0
Population divergence times of C. ryukyuensis (2.2–2.8 Mya) and two subspecies of mainland Asian mandarins (C. reticulata): common mandarin and mangshanyeju (1.4–1.7 Mya). Extant common mandarins are recent admixtures with both mangshanyeju and pummelos
source: https://www.nature.com/articles/s41467-021-24653-0#MOESM8
- Author: Ben Faber
The Vertebrate Pest Council hosted a series of seminars this spring that provided updates and information on managing vertebrate pests. The series was popular, and several individuals who were not able to attend requested that we provide this content a second time. As such, we have again partnered with Target Specialty Products to provide a second offering of these three 2-hour sessions. The new dates and sessions include:
Day 1 (Sept 28): Field rodents
Day 2 (Sept 29): Updates and information on the use of rodenticides
Day 3 (Sept 30): Managing commensal rodents
To be clear, if someone received credit for participating in a session back in the spring, they won't be able to receive credit a second time. However, perhaps there will be a new session of interest that they have yet to attend. Likewise, with the end of the year fast approaching, individuals may be seeking additional CE units to fulfill their DPR obligations. Perhaps these seminars will be of interest. These are unique seminars in that there generally is not any other place where you can get continuing education credits exclusively for vertebrate species.
CHECK OUT THE AGENDA ATTACHED
rodent webinar