- Author: Ben Faber
Wow, woolly whitefly covered with waxy, curly filaments , Aleurothrixus floccosus.
One of the consequences of fire and the resulting ash is that the biocontrol agents that keep whiteflies, scale, mealybug and other pests in balance is that they will spend so much of their time preening that they don't have time to go after their prey. Lacewing larvae, minute pirate bug, ladybird larvae, parasitic wasps and others rely on moving around to get at their food sources. When they cant move fast, they stop and clean their joints to stay limber. Whitefly and scale insects just hunker down and don't need to do a lot of moving. They just breed, and without actively moving biocontrol agents, their populations can explode. Or that's my human analogy. In dusty areas or areas affected by ash, the particles get in their joints and they need to spend time cleaning in order to move fast.
Whiteflies suck phloem sap, which in some cases can cause leaves to wilt and drop when there are high numbers of whiteflies. However, the primary concern with whiteflies is the honeydew they produce. Honeydew excreted by nymphs and adults collects dust and supports the growth of sooty mold; large infestations blacken entire trees, including fruit, as well as attract ants, which interfere with the biological control of whiteflies and other pests. The sooty mold can also affect tree yields by reducing photosynthesis and requiring extra handling time for cleaning.
So pests under good control prior to a fire can get out of hand. This is a good example of a tree in the town of Ventura where ash was a problem. A seemingly clean tree, free of whitefly, started to defoliate with blotchy leaf spots. On the undersides of the leaves corresponding to the blotches are colonies of whitefly. And looking closely you can see that some of the nymphs have exit holes, indicating that they have been parasitized by a wasp. So nature is kicking in and taking it's course. The whitefly should get cleaned up soon too by some forager, such as lacewing larvae or pirate bug. No need to spray because it would just be a further disruption.
See more about whiteflies at:
http://ipm.ucanr.edu/PMG/PESTNOTES/pn7401.html
Photos: Defoliating 'Meyer' lemon tree, blotches on upper side of leaf, whitefly colonies with exit holes in some of the nymphs
- Author: Ben Faber
A trunk "below grade", that is a buried trunk, is a problem for most trees. Willows and other riparian trees along water ways that are inundated regularly can adapt to a change in soil depth around their trunks. That's not true of most of our commercial tree species, and avocados and citrus are really susceptible to buried trunks/stems. they asphyxiate. This can be a very common problem at planting when a hole is too deep and the new tree settles in the loosen earth and gradually the stem is buried. Or, when the grower is doing the "right thing" and using an organic planting mix that gradually decomposes and the tree settles into the ground and the crown is covered by dirt. The tree then starts looking bad - leaves yellow. The canopy defoliates. All the while, the grower is putting on more water and more fertilizer and the tree looks worse and worse. Remove the soil from around the base, and voila, in a few months the tree is happy again. If the dirt isn't moved, the stressed tree is now susceptible to root rots, both Phytophthora and Armillaria. Those problems are a lot worse than just lack of air.
This suffocation is a common problem after flooding. Dirt from higher up moves into lower positions, gravity moving dirt can move a lot. It accumulates around the base of the tree. The grower is preoccupied with other things that occur with flooding and does nothing. A few months later, the trees start turning yellow especially when the weather warms up and they are more active and more water is being applied. Flooding can also spread disease organism from other areas that are contaminated. Oak root fungus is frequently spread in flooding waters, especially in the lower positions in little valleys.
Pulling that accumulated soil away from tree is important for tree health. It's something that needs to be done soon after the flooding incident, or any event that buries the tree trunk.
- Author: Ben Faber
The Latest on Florida's LW Disease
Recommendations for Laurel Wilt in Commercial Groves
Jonathan H. Crane, Tropical Fruit Crop Specialist1, Daniel Carrillo, Entomologist – Tropical Fruits1, Edward A. Evans, Agricultural Economist1, Randy C. Ploetz, Plant Pathologist – Tropical Fruits1, and Jeff Wasielewski, Commercial Tropical Fruit Crops Extension Agent2; 1UF/IFAS, TREC, Homestead, FL and 2Miami-Dade County Extension-UF/IFAS, Homestead, FL Website: http://trec.ifas.ufl.edu
Laurel wilt is a lethal disease that spreads rapidly among root-grafted avocado trees and for this reason necessitates frequent scouting to detect symptomatic trees and immediate tree removal to stop spread to adjacent trees. The research on the management of the laurel wilt pathogen and several ambrosia beetle vectors is continuing, therefore, recommendations for mitigation and control may periodically change.
This document describes the current recommendations to limit or prevent of the spread of the laurel wilt pathogen among avocado trees and to control the ambrosia beetle vectors of the disease. In addition, alternative management strategies concerning re-establishment of productive groves are discussed.
If you have trees symptomatic for laurel wilt please contact Don Pybas, LW Coordinator, (305- 247-0848; pybas@ufl.edu) or Jeff Wasielewski, Commercial Tropical Fruit Crops Extension Agent, (305-248-3311, ext. 227; jwasielewski@ufl.edu) for more information.
Disease symptoms of laurel wilt
The earliest external symptom of LW is green wilted leaves in sections of the canopy.
However, green-leaf wilting is quickly followed by desiccation and browning of these leaves, which remain attached to the plant stems for up to 12 months. Stem and limb dieback follow and eventually additional sections of the tree decline and the tree dies. Underneath the bark, the normally cream- white sapwood may have dark blueish-black streaks. Frequently, trunks and/or limbs may have numerous small diameter holes with sawdust tubes (toothpick-like protrusions from the bark), and/or sawdust clinging to the bark which is evidence of ambrosia beetle activity (i.e., boring into the tree).
Two main strategies for controlling the spread of the laurel wilt (LW) pathogen
- Frequent scouting to detect trees with green leaves beginning to wilt (i.e., early symptoms of LW) and their immediate uprooting and destruction.
- Infusion or injection of Tilt® fungicide into all the trees in a grove before a LW outbreak occurs. Repeated applications at an 8 to 18 month interval are necessary.
Of the two strategies mentioned above, the early detection-immediate destruction method is the most economical. Repeated infusion of fungicides may cause damage to the trees at the infusion sites and therefore may not be sustainable. In contrast, there is antidotal evidence that repeated injections are less damaging to the trees but there is a lack of information on the long-term sustainability of this method.
Primary strategy: early detection and tree sanitation (rouging)
A helicopter survey implemented by the Avocado Administrative Committee was important in alerting the industry and growers to new areas of potential LW infestation and is now important for monitoring on-going infestations. However, helicopter surveying is expensive and not frequent nor detailed enough to detect early green-leaf wilting caused by laurel wilt.
Scouting frequently is key in detecting LW affected trees at the green-wilt stage. Ground-based scouting by driving through groves via equipment (e.g., tractors, mowers, and spray equipment), trucks, and ATVs is possible. However, detecting early symptoms of LW in the tops of trees may be difficult by just driving. An alternative is the use of drones, which can cover large areas quickly, and in detail. However, there are Federal Aviation Administration requirements and regulations that must be met in order to operate commercial drones. Canine detection of LW is an additional detection method. The canines detect the LW pathogen in pre- and fully symptomatic (e.g., desiccated leaves, tree dieback) trees. In many cases, fungicide infusion of infected but pre-symptomatic (no outward signs like wilting) trees allows these trees to remain productive, however fungicide re-treatment is necessary. In addition, early detection by canines provides time to remove pre-symptomatic trees to prevent further root graft spread of the pathogen to healthy trees. The number of available trained canines and for some producers, the cost, may limit the use of canines.
The major component of LW control is to remove and destroy LW affected trees at the green- wilt stage. Do not hesitate to remove and destroy a green-leaf wilted tree – waiting to see if more of the tree canopy develops symptoms or turns brown allows time for the pathogen to spread to adjacent trees through their connected root systems. Waiting to remove and destroy the LW affected tree reduces the chance tree removal alone will stop the spread of the LW pathogen to neighboring trees.
The LW pathogen can survive in declining and dying trees and the only way to stop movement of the pathogen to adjacent trees is to remove (uproot) affected trees immediately. Just stumping or hatracking LW affected trees will not stop the pathogen from moving to adjacent trees through root grafts among adjacent trees. In addition, trees that are affected by LW are very attractive to ambrosia beetles. If these ambrosia beetles come into contact with the LW pathogen inside the tree, these beetles and their offspring may be contaminated with and spread the pathogen to more trees and groves. Therefore, proper destruction of LW affected trees is an important component for reducing the spread of this disease by root grafts and by ambrosia beetles.
Steps for properly removing and destroying LW affected trees
- Remove the entire tree by pulling or pushing. Pushing trees over before tree destruction is easier than trying to dig or uproot stumps from the ground.
- Once the tree has been removed, it should be chipped or burned. High powered front-end grinders are now in use which quickly chip the entire tree including the trunk area. Alternatively, wood may be chipped and wood too large split then chipped or burned. Call FDACS-Div. of Forestry at 305-257-0875 or 954-475-4120 for permission to burn (burn permit). Wood cut into smaller pieces will burn faster and more completely. The large wood may need to be burned more than one time (restack to expose non-burned wood) in order to be destroyed.
- Treating the tree stump (or stumps) with insecticides does not prevent the emergence of ambrosia beetles, which are already inside the tree and after a few weeks does not prevent further ambrosia beetle infestation. Thus, the best method to prevent beetle emergence from this wood and new boring into the wood is to dispose of the wood by chipping and/o rburning.
- Ambrosia beetles are attracted to avocado wood chips and leaving them untreated or not burned results in increased activity of ambrosia beetles in the grove. Wood chips should be spread out, not mounded, and thoroughly sprayed twice, 7-days apart, with an approved insecticide (e.g., Hero®, Talstar®, Malathion, Danitol® or Agrimek®), plus adjuvant (i.e., NuFilm®, Vapor Gard® or Pentrabark®). Some biopesticides (e.g., BotaniGard) have also been shown to kill ambrosia beetles as well. Avocado groves under organic production should chip and burn all wood.
Secondary strategies for preventing the spread of LW by root grafts among adjacent trees
Prophylactically treat entire planting with systemic fungicide
At present, there are no fungicides that cure LW-affected trees. The fungicide Tilt® (propiconazole) can be used, but it must be inside the tree before they are infected with the laurel wilt pathogen. Currently, Tilt® is the only labeled fungicide approved for laurel wilt control on avocado trees. Tilt® can only be used in commercial operations and is not approved for use by homeowners in their landscapes. When using Tilt®, growers must have in their possession the Section 18 special local needs label (SLN); go to http://www.syngenta-us.com/ or contact Jeff Wasielewski, Commercial Tropical Fruit Crops Extension Agent, (305-248-3311, ext. 227; jwasielewski@ufl.edu).
Infusion. Infusion consists of diluting the Tilt® with water and either passively or under pressure infusing the mixture into the flare roots at the base of the tree. Infusion of Tilt® must be repeated every 8 to 18 months. While effective, the infusion method causes damage to the flare roots making re-treatment difficult. Therefore, this application method may not be sustainable.
Injection. Injection consists of injecting the tree along the trunk and the major scaffold limbs using undiluted (or slightly diluted) Tilt®. Injection of Tilt® must be repeated every 12 to 16 months. Although a substantial number of groves have been treated in this manner, whether this method is sustainable in the long-term is not known.
Prophylactic treatment of groves, whether by infusion or injection, can be costly. As such this strategy if chosen is best suited for groves with varieties that generate relatively high returns.
Spot treatment. This is a combination strategy of early detection of LW symptomatic trees and treating by infusion one to two healthy trees adjacent a LW affected tree in an effort to prevent root movement of the LW pathogen to healthy trees. However, the key to success with the spot fungicide treatment is early detection of trees with symptoms of LW, their immediate uprooting and destruction and immediate infusion with Tilt® fungicide to the healthy adjacent trees. Although the spot treatment method is generally less costly than treating an entire grove approach, it may not be sustainable because of the damage to the flare roots caused by the necessity of repeated fungicide applications.
Ambrosia beetle suppression - insecticide applications in the immediate area (1 acre) surrounding LW positive avocado trees
The largest portion of the ambrosia beetle population is inside infested trees. Contact insecticides will not prevent ambrosia beetle emergence from already infested trees or wood.
Chipping and burning wood are the only ways to eliminate ambrosia beetles inside tree stumps and wood and stop their reproduction. To suppress ambrosia beetles active in the environment after chipping and/or burning infested trees, applications of contact insecticides and/or biopesticides to about one acre of trees surrounding a LW affected tree is recommended. After removing LW affected trees, make two applications of insecticide directed to the trunk, scaffold limbs and medium to large wood (not the foliage) of adjacent trees at a 10-15-day interval. The spray should be bark directed spray to the lower part of the tree and not the leaves and upper canopy. Malathion, Danitol® and Agri- Mek®SC are registered for bearing avocado trees. In order to reduce the chances of beetle resistance these products should be rotated (Table 1). For Malathion and Danitol® use an adjuvant such as NuFilm® to prolong the efficacy of the insecticide. Do not use sticker-type adjuvants like NuFilm with Agri-Mek®SC use a non-phytotoxic, non-ionic activator type wetting, spreading and/or penetrating spray adjuvant or horticultural oil (not dormant oil) – see label for details. Do not use Vapor Gard® and Pentrabark® adjuvants as they may cause phytotoxicity on leaves. For non-bearing avocado trees, Talstar®-S and Hero® may be applied (Table 2); use an adjuvant to prolong their efficacy.
The biopesticides BotaniGard® ES and Mycotrol® (the active ingredient is Beauveria bassiana
or Bb) are registered for avocado and have been shown to provide some ambrosia beetle control. The strategy is to attempt to suppress the ambrosia beetle population increase, which occurs during the spring. Research has shown trunk directed applications of Bb are capable of killing ambrosia beetles and the time-line for application of these materials is February through May when average temperatures are lower and beetle populations are increasing. However, proper trunk and major limb directed application is paramount for Bb to be effective. The concept is to place live Bb spores on the main trunk and scaffold limbs where ambrosia beetles may contact the live Bb spores.
- First, compatibility of Bb with other spray materials varies. A general recommendation is to clean spray tanks prior to tank mixing. Bb is not compatible with some fungicides (e.g., Abound® and Switch®) and insecticides (e.g., Danitol® and Malathion) (Table2).
- Spraying Bb too close to an application of a non-compatible spray material application will reduce the effectiveness of ambrosia beetle control. Therefore, time Bb applications toh ave the most time before and after any potential non-compatible spray material is used.
- Only purchase what will be used immediately. Do not leave these bio-insecticides in the tank for prolonged periods since it will kill the active Bb spores. Also be sure to store BotaniGard® ES and Mycotrol® in a cool, dry place that stays between 40°F and 85°F – otherwise the Bb spores will be killed.
- Mix the BotaniGard® ES and Mycotrol® in sufficient water to ju st wet the trunk and major limbs. Do not spray to run-off as this causes the Bb spores to wash off the bark. A light but thorough wetting is ideal.
In general, ambrosia beetles are attracted to areas of low light levels (i.e., shade). To reduce the potential for ambrosia beetle attack, selective pruning and/or annual or biannual topping and hedging should be practiced to increase light levels within the grove and tree canopies.
Summary
Ambrosia beetle control is a part of the strategy to control laurel wilt. However, it is imperative to implement early scouting for laurel wilt symptomatic trees and for tree removal and destruction to occur quickly. Strategies to suppress the ambrosia beetle population include selective pruning and/or regular topping and hedging to reduce the shading within and among avocado trees. This may reduce the attractiveness of trees to ambrosia beetles. Actively controlling ambrosia beetles in the immediate vicinity of an active laurel wilt outbreak may reduce new laurel wilt outbreaks.
Economic considerations
Rogue (remove and destroy) and replace
Economic modeling indicates that early detection and removal of the infected avocado tree (primary strategy) plus replacement (i.e., replanting) provides the best option for the operation to remain profitable. Immature trees are less likely to be attacked by ambrosia beetles and are not root grafted to adjacent trees. Harvesting can commence from third or fourth year.
Stumping and top-working trees
Stump healthy trees to 3 to 5 ft in height (~$25/tree) and allow trees to resume production.
Alternatively stump trees and topwork (~$35/tree) trees to a more profitable cultivar. Production may resume in 2-4 years depending upon cultivar and production practices. Their production level will be at a higher level than young (1-3 years-old) trees. The drawback for maintaining these older trees is they remain root grafted to adjacent trees and LW could move from tree to tree via the root system. It is not recommended to stump LW affected trees to topwork.
Replanting
Remove a block or grove of old avocado trees (~$50/tree) and replant avocado trees (~$30/tree) with a more profitable cultivar. To establish a new grove estimated to be ~$8,000/acre. The advantages to removing mature root-grafted avocado trees and replanting to young avocado tree includes: (1) young trees are less attractive to AB (small diameter trunks and lots of light in grove) and (2) young trees are not and will not be root grafted to adjacent trees for years – so LW pathogen cannot spread tree to tree by the roots. This strategy buys time to find better control solutions to LW-AB. The disadvantages to remove and replanting with young trees is the cost of removing old trees and replanting with young trees, fruit production will not begin for 3-4 years, and will not be substantial until 7-8 years.
Alternative options for LW affected groves
Remove trees (~$50/tree) and enter an alternative agricultural business or fruit crop.
Table 1. Contact insecticides for ambrosia beetle control. Direct applications to the trunk and medium to large wood to about one acre of trees surrounding the LW affected tree. Rotate pesticides products reduce the potential for insect resistance. MixDanitol®,Malathion and Hero® with anadjuvant (e.g.,NuFilm®) to prolong their efficacy. ForAgri-Mek®SC do not useNuFilm® or similar, use a non-phytotoxic, non-ionic activator type wetting, spreading and/or penetrating sprayadjuvant or horticultural oil (no a dormant oil) – see label for details. The biological control insecticidesBotaniGard® ES andMycotrol® do not need anadjuvant and should be stored in a cool (<85°F), dry place.
Product |
Rate per acre |
Spray interval |
Potential # of applications allowed per year per acre |
Comments – estimated days of efficacyz |
Danitol® 2.4 EC (fenpropathrin) |
21.3 oz |
14 |
1 |
14-21 |
Malathion 5EC (malathion) |
24 oz/100 gallons |
7-10 |
Open |
10-14 |
Hero® (liquid)y (zeta-cypermethrin+ bifenthrin) |
10.3 |
14 |
6 |
14-21 (non-bearing trees only xy) |
Agri-Mek®SC (abamectin) |
4.25 oz |
30 |
2 |
Do not mix with NuFilm or similar; see label for details |
Talstar®S (bifenthrin) |
40 oz |
NA |
1 |
Not known; non-bearing trees onlyy; may not need adjuvant |
BotaniGard® ES (Beauvaria bassiana) |
32 oz |
7-14 |
Open |
Not known |
Mycotrol-O® (Beauvaria bassiana) |
32 oz |
7-14 |
Open |
Not known; organic production |
x, Special Local Need (SLN Section 24C): y, Only for non-bearing trees; do not apply within 1 year of harvest; z, The estimated days of efficacy is influenced by numerous factors including weather conditions (e.g., rainfall, temperature, and UV light intensity). |
Table 2. Compatibility of fungicides, insecticides, adjuvants and foliar nutrients with BotaniGard® |
||
Fungicide |
BotaniGard |
|
Pre-application |
1 h |
6 h |
Abound |
NC |
NC |
Cuprofix-Ultra 40 Disperss |
C |
C |
Flopan 80 |
NC |
NC |
Kocide 2000 |
C |
C |
Ridomil Gold Copper |
C |
C |
Ridomil Gold SL |
C |
C |
Switch 62.5WG |
NC |
NC |
Tilt |
C |
C |
ProPhyt Phosphonate |
C |
NC |
C = compatible; NC = Not compatible |
|
|
Compatibility of insecticides with BotaniGard® |
|
Insecticide |
BotaniGard |
|
Pre-application |
1 hour |
6 hours |
Danitol |
NC |
NC |
Hero |
C |
C |
Admire Pro |
C |
C |
Malathion |
NC |
NC |
Permethrin |
C |
NC |
Agrimek |
C |
C |
Actara |
C |
C |
Talstar |
C |
C |
Mustang |
C |
C |
C = compatible; NC = Not compatible |
||
Compatibility of adjuvants with BotaniGard® |
||
Adjuvant |
BotaniGard |
|
Pre-application |
1 hour |
6 hours |
Banole oil |
C |
C |
Citrus oil |
C |
C |
NuFlim |
C |
C |
L1700 |
C |
C |
Pentrabark |
C |
C |
Compatibility of KeyPlex 350 with BotaniGard® |
||
Pre-application |
1 hour |
6 hours |
Keyplex 350 |
C |
C |
C = compatible; NC = Notcompatible |
|
(c://tree destruct and LW control recommendations 12-22-17.doc)
- Author: Cheryl Wilen
IPM Natural Resources Extension Coordinator
Endemic and Invasive Pests and Diseases Strategic Initiative Leader
UC Statewide IPM Program & UCCE- You need to get a Remote Pilot Airman Certificate (FAA Part 107) if you are going to do anything commercial with it. That includes even if you are using it on a job where you will not be paid.
- You can use it for scouting but you can't fly it over people (unless you get a waiver). You also always have to have it in your or an assistant's (the spotter with radio communication) line of sight.
- Even if you have a drone that is capable of doing a spray application, the Dept. of Pesticide Regulation currently requires that the drone pilot have an Airman's Certificate (Pilot's license). This is addition to the Pest Control Aircraft Pilot Certificate from DPR. However, things may change in 2018. See pages 3-47 to 3-52 in http://www.cdpr.ca.gov/docs/enforce/compend/vol_1/entirerep.pdf
2017 The Regents of the University of California. All Rights Reserved
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- Author: Jesse Morrison
Have you ever thought about it? I'm sure a lot of you have…what's the biggest living thing on earth? If you're like me, you immediately think of animals like the blue whale. In this case, we're just talking about organisms that spend their life predominantly or entirely on land. Anybody thinking of the rhinoceros, or maybe the African elephant? Nope!
The answer to this question might surprise you. The largest terrestrial organism on the planet is actually a fungus! Not your typical, garden-variety mushroom, but a fungus, nonetheless. And while it is edible, it comes with a few problems. Its common name is honey fungus.
The soil is filled with living organisms, large and small. Bacteria are the most numerous soil organism – there can be more than a million in a teaspoon of soil! There are over 10 trillion types of soil bacteria!
There are “only” 100 billion types of soil fungi, but they play in important role in the life cycle within the soil. Fungi break down decaying plant material into nutrients that other plants can use to grow. They soak up water in water-logged soils. You might be familiar with seeing mushrooms growing on moist logs, or in soil with wet leaves.
Honey fungus is a bit different from many other fungi. It's not one that landowners will welcome because it can kill trees. In fact, it gained fame in the late 1990s as the “culprit” that was killing fir trees in the Pacific Northwest. (Fir trees are widely sought after as beautiful landscape plants, Christmas trees, and for lumber used in building homes.)
Honey fungus is a parasite – Armillaria solidipes. Parasites are organisms that live off other organisms, sometimes hurting them. Honey fungus is widely distributed across the cooler regions of the United States and Canada. It is very common in the forests of the Pacific Northwest.
These fungi grow in individual networks of above and below-ground fibers called mycelia. Mycelia work in a similar fashion to plant roots. They draw water and nutrients from the soil to feed the fungus. At the same time, they make chemicals that are shared with other organisms in the soil. Sadly for the fir trees, the honey fungus can kill already weakened or stressed trees. The natural action of this fungus can be destructive in forests, leading to widespread die-off in timber stands.
One cool feature of the underground network of mycelia of all fungi is that they help hold soil particles together. Just like plant roots, mycelia work to prevent soil particles from blowing away in the wind or being taken away by running water. They are a very important part of the soil ecosystem.
Scientists have shown that Armillaria solipipes identify and connect to each other. That's right: when mycelia from different individual honey fungus bodies meet, either in or on the soil surface, they can attempt to fuse to each other. The fungi must be genetically identical honey fungi. When the mycelia successfully fuse to each other, they link very large fungal bodies together. This, in turn, changes extensive networks of fungal “clones” into a single individual.
The largest honey fungus that has been identified in North America is located in Oregon. It measures 3.4 miles across! Scientists also believe that this particular honey fungus may be over 2,000 years old. The next largest honey fungus is in the neighboring state of Washington.
While honey fungus is impressive in both age and size, it isn't always a favorite of scientists and landowners because of its parasitic nature. But it is the largest organism on earth, and scientists have had only a few decades of research to understand how mycelia fuse and communicate. Perhaps one day, research discoveries about honey fungus could lead to a new medicine (think Penicillin), or new ways to grow food – the possibilities are endless!
And this is the largest terrestrial organism. Who knows what lurks in the depths of the ocean?
P.S.
Armillaria solipipes is one of the many species that was once lumped as Armillaria mellea, oak root fungus. So many woody perennials are susceptible to this fungus. It turns out that avocado for whatever reason tends to be somewhat more tolerant of oak root fungus than many other trees. Under stress, it too will succumb, though.