- Author: Sonia Rios
Sonia Rios, Area Subtropical Horticulture Advisor, Riverside & San Diego Counties
Henry Herrera, Forester, California Department of Forestry and Fire Protection (CAL FIRE)
Gary Bender, Subtropical Horticulture Advisor, San Diego County
This is a reposting of a blog from 2015 that is still pertinent today.
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
- Author: Ben Faber
A third day for applying for USDA - Farm Service Agency/Natural Resources Conservation Service Disaster Relief has been added. Applications can also be made at the FSA offices listed at the end of this message, but the times and venues listed here are for the convenience of fire-affected producers in these two counties.
The USDA's Farm Service Agency and Natural Resources Conservation Service will have workshops to aid agricultural producers; including cattle, tree, nursery, vegetable, and berry farmers in filing for federal assistance programs. Appointments can be arranged now for filing applications during these workshops.
The California Avocado Commission and University of California Cooperative Extension (UCCE) are coordinating with the USDA's Farm Service Agency (FSA) and the Natural Resources Conservation Service (NRCS) the availability of field appointments for growers who have been impacted by the Thomas Fire. Personnel from both FSA and NRCS will be available to assist growers with the necessary paperwork to apply for federal assistance.
The three days of appointments are available (information below). To schedule an appointment for one of the following three days, please call (805) 645-1434.
Tuesday, December 19th, 2017
Santa Paula Agriculture Museum
926 Railroad Ave, Santa Paula
8:00 am – 4:00 pm
Wednesday and Thursday, December 20th and 21st, 2017
University of California Cooperative Extension
669 County Square Drive Suite #100, Ventura
8:00 am – 4:00 pm
Federal relief personnel will be available to assist growers with the paperwork, and growers are asked to provide the following information:
- Business entity information (e.g. individual, limited liability corporation, etc.)
- Social Security Number and/or Employer Identification Number
- Location/size of the farm
- Extent of damage
In addition, it's important that California avocado industry members who have been impacted by the recent wildfires and/or Santa Ana winds contact their crop insurance agent within 72 hours of the event to determine possible applicable coverage. Both fire and wind events may be included in certain crop insurance coverage, but agents must be notified within 72 hours.
Below, again, is a list of potential FSA programs that may provide disaster assistance to those avocado growers affected by the wildfires:
- The Tree Assistance Program provides financial assistance to qualifying orchardists to help them replant or rehabilitate trees damaged by natural disasters (separate from crop insurance).
- The Emergency Conservation Program offers funding and technical assistance to growers to help them rehabilitate land damaged by natural disasters. This program may provide cost share assistance for debris removal, land leveling and shaping, irrigation replacement, and cattle fencing.
- Emergency loans are available to producers located in counties that receive a primary or contiguous disaster designation.
Remember, if you are an impacted grower/cattle producer you are asked to contact both FSA and your county agricultural commissioner's office as follows:
USDA-Farm Service Agency
Santa Barbara/Ventura County
Daisy Banda
Key Program Technician
Daisy.Banda@ca.usda.gov
805-928-9269 Ex.2
Riverside/San Diego Counties
Desiree Garza
County Executive Director
desiree.garza@ca.usda.gov
760-347-3675 ext. 107
Ventura County
Korinne Bell, Chief Deputy Agricultural Commissioner, Korinne.Bell@ventura.org
Henry Gonzalez, Agricultural Commissioner, Henry.Gonzales@ventura.org
(805) 388-4343, Ext. 2
Santa Barbara County
Debbie Trupe, Deputy Agricultural Commissioner, dtrupe@agcommissioner.com
Stephanie Stark, Deputy Agricultural Commissioner, sstark@agcommissioner.com
(805) 681-5600
San Diego County
Vince Acosta, Information Technology Principal, vince.acosta@sdcounty.ca.gov
(858) 967-8623
Riverside County
Ron Bray, Assistant Agricultural Commission, RBray@RIVCO.ORG
(951) 955-3000
A complete list of FSA disaster assistance programs can be found online. For more information about available disaster assistance programs, contact your local U.S. Department of Agriculture office. You can find your local USDA service center by clicking on this link.
- Author: Ben Faber
After the fires, the question has come up of whether an orchard should be replanted or topworked in the field, possibly to a new variety. This has been an issue in the past and was addressed in a little study nearly 20 years ago. The study still bears relevance today and applies to both avocado and citrus. The availability of avocado trees for replanting is in serious short supply, so replanting may not be an option at this point.
There are many changes going on in the citrus industry and one opportunity is the conversion of an orchard to another variety of citrus. If this is a consideration, then the question becomes one of whether the orchard should be topworked or replanted with new nursery trees. If the trees are healthy and under 20 years of age (it is possible to topwork older trees) and the new scion is compatible with the interstock or rootstock, then topworking can come into production sooner than a new replant. If the planting density needs to be changed or serious soil preparation or a new irrigation system needs to be installed, then replanting might be the preferred choice.
The chance to convert is also dependent on the availability of new trees and budwood. New varieties can often be in short supply. It's best to make sure that for either option that the material is there. For topworking, T-budding is more conservative of material than stick grafting. If topworking is chosen, then it must be decided whether to graft the scaffold branches or the stump. Stump grafting makes for a lower tree, but scaffold grafting reduces the risk of losing the topworked tree from damage to the graft from birds, pests, wind or frost.
It is often assumed that topworking is cheaper than replanting, but as the following example shows, it probably is not. In Santa Paula, ‘Olinda' Valencias on ‘Carrizo' rootstock were converted to scions ‘Allen' Eureka lemon, or ‘Powell' late navel. In 1998 and 2000, the ‘Olinda's were interplanted with either ‘Allen' on ‘Macrophylla' or late navel ‘Powell' or ‘Chislett' (on either ‘Carrizo or ‘C-35' rootstocks). The ‘Olinda's were topworked in 2002 and 2003 to one of the new scions. In a few cases, ‘Allen' was stump grafted, but most trees were scaffold grafted.
Several steps are required for topworking that will ensure success. These are listed below:
• Get a reputable person to do the work.
• Time of year is critical for grafting. Spring is best.
• Leave a nurse limb.
• Decide to stump or scaffold graft.
o Stump grafting requires only 3 – 4 buds or sticks
o Scaffold grafting requires 2 buds per scaffold. Consider winds since even one-year old unions are very tender.
• Sequence of events
o Line up budwood
o Remove top of tree and stack brush
o Whitewash trunks
o Paint cutoff surfaces
o Insert grafts
o Wrap grafts with plastic tape
o Place white paper bag over grafts and tape in place
Later
o Keep after ants and snails
o Shred brush
o Remove bags when shoots start growing through them.
o Bi-monthly, in first year, brush out water sprouts. Less often in the next 2 years
Much of this work can be contracted with the grafter, who usually assures some level of performance, something like 90% take. It is up to the grower to ensure that pests do not take out the grafts.
The costs of topworking are associated with the costs of the budwood (as much as $3 per tree), the act of grafting (depending on stump or scaffold, $8-10 per tree) and water sprout removal. Sprout removal is six times in year one, eight times in year two and only four times in year three. At a labor rate of $12 per hour, sprout removal costs $7.20 per tree.
A like for like comparison of topworking versus replanting based on 2002 data is shown below.
So in the case of both the lemon and navels it costs a bit more to topwork, but the results are earlier production. Here the topworked trees gain the economic advantage. For example, if cultural costs were $1000 per acre per year (20 by 20 ft. spacing) and, conservatively, two years are saved, the maintenance savings per tree would be $18. In the above study the time advantage appears even greater. Three-year old topworked lemons produce about the same as 6-year old replants. Two year old topworked navels have a significantly larger canopy than six-year old replant navels and appear to have about the same fruit set for the coming year.
- Author: Ben Faber
The USDA's Farm Service Agency and Natural Resources Conservation Service will have workshops to aid agricultural producers; including cattle, tree, nursery, vegetable, and berry farmers in filing for federal assistance programs. Appointments can be arranged now for filing applications during these workshops.
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- Author: Ben Faber
The destruction after a fire can be pretty gruesome and sad. Many times, though the fire moves through the orchard so fast that, even though the canopy has turned brown, there is a good chance the trees can come back. It all depends on how much damage has been done to the trunk. If the fire has substantially damaged the base of the trunk, it is unlikely to come back, even if the canopy is still green. That is the saddest thing, because you think you've dodged the bullet, but if the trunk is too damaged, the canopy collapses gradually over a few weeks. However, the canopy may look a goner, but if the trunk is still intact, the tree will come back and may still be as productive as before.
The thing to look for at the base of the trunk is the discoloration. If it's black, it's probably not coming back. However, it can come back if after a few weeks you don't see the pencil-sized cankers that indicate that the sap has bubbled to the surface (see photo 1 below). If after a few weeks, the trunk is still clear of those bubbles (photo 2), even though the canopy looks gone, it is quite likely to come back.
Aside the boils and exudates near the trunk base, a clear sign of damage that limits tree success is when suckers start pushing from the base of the tree. The roots start pushing new vegetative growth when there is trunk damage that has been significant. You may end up nursing those suckers to graft them to a new tree, but end up removing the original tree.
It's also possible that there is damage in just one part of the trunk and not on the rest of the tree. In this case, it can also come back. The problem with these cases, is that they may come back, and given enough time will be good trees again. But if they haven't recovered enough and there's a sudden heat spell, they may go down suddenly as if they had been burned again. That's the way they will look, like they have been burned again. Given enough time, though the avocado will grow from good areas to cover the poor areas and the tree may be productive again.
Avocados are amazing in their ability to recover. Eucalyptus can do it. But you singe the trunk of a lemon, and good-bye lemon.
Fire Information:
http://ceventura.ucanr.edu/Agricultural_Threats/Fire_Information/
Photo 1 and 2.