- Author: Ben Faber
Laurel Wilt Disease (LWD) is caused by the fungus Raffaelea lauricola and is transmitted to host trees by the redbay ambrosia beetle (Xyloborus glabratus) (RAB). During 2002 this exotic beetle was introduced into Port Wentworth, GA, via infested solid wood packing material. Since then, LWD has spread naturally the RAB vector and humnan movement of infested wood throughout the southeastern U.S. (GA, SC, NC, FL, and MS), eliminating redbay (P. borbonia), swampbay (P. palustris) and other native members of this family. This pest has spread to most counties in Florida and to the commercial avocado-growing area near Miami.
Trees in the Lauracae, including the commercially important avocado (Persea americana Mill.) are threatened by laurel wilt (LWD). Research has shown that avocado trees are susceptible to attack by the RAB and susceptible to LWd. In Jan., 2010, the RAB was detected approximately 16 km from the edge of Florida's primary commercial avocado production area in southeastern Miami-Dade County, and in Feb., 2011 LWD was confirmed in dying swampbay trees in the same area. As of April 2012, LWD was confirmed in several commercial avocado groves in the northeastern section of the industry. Despite intensive research since 2006, no economically viable chemical control measures have been found to combat LWD. However, on-going research is promising and has provided the researcher and extension scientists the basis for suppression of RAB and the spread of LWD. Thus, detection and immediate suppression of outbreaks of LWD within the avocado production area is viewed as the most appropriate LW management strategy.
A group of Florida researchers recently visited with CA growers to about their progress confronting this problem. Their talks are available for review at this site:
http://ceventura.ucanr.edu/Com_Ag/Subtropical/Avocado_Handbook/Laurel_Wilt_Disease_in_Florida/
Photo: A Fast Death for an Avocado
- Author: Ben Faber
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, Emeritus, 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
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.
- Author: Ben Faber
“Laurel wilt – A threat to California's avocado industry”
Presented by: California Avocado Society, Inc., California Avocado Commission, University of California Cooperative Extension, and University of Florida's Tropical Research and Education Center. Event is FREE, everyone is welcome!
- Tuesday, July 30, 2019, 9-11 AM.,
Pala Mesa Resort, Fallbrook
- Wednesday, July 31, 2019, 9:00 a.m. to 11:00 a.m.,
UC Cooperative Extension Office Auditorium, 669 County Square Dr. Ventura, CA 93003
- Thursday, August 1, 2019, 9-11 AM.,
San Luis Obispo Farm Bureau Office
Agenda
The current status of Laurel Wilt in South Florida
Laurel Wilt epidemiology and management
Laurel Wilt Vectors and Management
Vascular physiology, anatomy and susceptibility of different avocado cultivars
Economic impact of control strategies
- Author: Ben Faber
UC Riverside is testing whether a sesame seed-sized wasp can control a pest that could seriously damage California crops including wine, walnuts, and avocados.
The pest, a sap-sucking spotted lantern fly, is originally from China and was first detected five years ago in Pennsylvania. Since then, large populations have spread rapidly to grape vines, apple trees, and other plants in New York, Delaware, New Jersey, Maryland, and Virginia.
Experts believe the lantern fly is likely to make its way to California soon.
Mark Hoddle, director of the Center for Invasive Species Research at UC Riverside, explains why the lantern fly is so harmful.
“It secretes copious amounts of “honeydew,” a waste product that encourages black, sooty mold and damages a plant's ability to grow,” he said. The honeydew also attracts undesirable insects such as ants and hornets.
The impacts could extend well beyond California. According to industry reports, the state is the world's fourth-largest wine producer, selling an estimated $35 billion domestically and exporting $1.5 billion annually.
Around 44% of nonnative insects arriving in California were first established elsewhere in the U.S. Given the speed with which the spotted lantern fly has spread, Hoddle realized the state needed a proactive approach to this predictable problem.
“Normally, when a bug shows up, we try to contain and eradicate it,” Hoddle said. “But by the time the population is found, it tends to already be widespread and hard to handle.”
The state Department of Food and Agriculture recently granted Hoddle $544,000 to test whether a tiny parasitic wasp, also originally from China, could be the solution to the looming problem. Hoddle explained that the wasp has a needle-like appendage it uses to lay its own eggs inside the lantern fly's eggs. While developing, the wasp larvae eat and kill their hosts, and then emerge after chewing escape holes through the lantern fly eggs.
These wasps pose no threat to plants or people, but before they can be used to control the lantern fly, Hoddle must prove they won't cause unnecessary harm to other native insects. “We can't just release a Chinese parasite into the wild in California,” Hoddle said. “Chances are low it will harm the wrong targets, but we have to be sure.”
Safety testing will be conducted in a highly secure quarantine facility at UC Riverside. Native lantern flies, the subjects of safety testing, will be collected from natural areas in California and southern Arizona this summer.
Though the wasp is now being evaluated as a biological control on the East Coast, populations of lantern fly there have already grown large enough to cause significant concern for the grape industry, Hoddle said.
A spotted lantern fly's wingspan is about 1.5 inches, and at most they can fly a few hundred feet at a time if they're assisted by the wind. The lantern fly has spread so fast in part because the females lay eggs on nonbiological materials, such as train cars, motor homes, wooden pallets, and trucks that inadvertently move them into new territories.
“Anyone on the East Coast driving to California should be especially vigilant about checking their vehicle for egg masses before they make the journey,” Hoddle warned. “Failing to notice them could have serious consequences.”
Hoddle's testing will take roughly three years, and he estimates that this may be around the time when the wasps will be needed in California. “We hope to be ready to release these wasps immediately when the spotted lantern fly shows up, giving us a really strong head start on the invasion,” he said.
reposted from: https://news.ucr.edu/articles/2019/06/17/looming-insect-invasion-threatens-california-wine-and-avocados
Great video of Lantern Fly life stages from Penn State
https://www.youtube.com/watch?v=Wumtju2_0JM
Photo: Lantern fly egg mass
/article>- Author: Ben Faber
Update on invasive shot hole borers: Online training now available
By Sabrina Drill, Natural Resources Advisor, UCCE Ventura
Invasive shot hole borers (ISHB) are a pest and disease complex potentially affecting over 200 tree species, but posing a strong risk to box elders, sycamores, and other riparian and urban trees, as well as being a nuisance pest for avocado. The beetles have also been shown to attack a wide variety of common and less common ornamental species. For a complete host list, visit https://ucanr.edu/sites/pshb/overview/SHB_Reproductive_Hosts/. The tiny beetles burrow into the trunks and branches of trees and create galleries where they cultivate a fungus that utilizes the trees own circulatory system, harming and in some cases killing the tree. We know the beetle can reproduce in over 60 species of trees, and they have devasted natural riparian areas, though we are beginning to see recovery of some infestations. Currently, the most effective management method is to remove infested wood, sometimes entire trees, and chip what is removed to minus 1”.
ISHB are now firmly established in Ventura County, with finds throughout the Santa Clara River Valley in traps from South Mountain to Toland Park in Santa Paula, and several infested box elder and sycamores in Meiner's Oaks and Ojai. It appears not to have crossed into the county in the south, but there are still active infestations in western Los Angeles County.
Personnel from UC ANR, CDFA, the Ventura County Agricultural Commissioner, and the US Forest Service have taken lead roles in developing a statewide ISHB action plan for the California Invasive Species Advisory Committee, with an initial investment of $5 million to work on controlling the pest. Plan elements include research in the ecology and control of the pest, including work to develop biocontrol; an early detection and surveillance program; addressing green waste and other pathways of spread, and outreach and education.
In terms of education and outreach, an area where Cooperative Extension in Ventura, LA, Orange, and San Diego counties have led, we're excited to announce the release of a new on-line training course. Available through our website, https://ucanr.edu/sites/pshb/, the course is actually served by the eXtension on-line learning platform (and users will need to create a free account). The course consists of 4 chapters including history and impacts, biology, symptoms and look-alike pests, and monitoring and management. While it can't fully replace a field training, it can be a good way to familiarize new staff to the issues.