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Care of Fire or Frost Damaged Trees
Recent and recurring fires are a problem where both citrus and avocado are grown in California.The winter forecast is out from NOAA and it looks like there might be frost in our future. What do you do if it hits your trees? https://www.noaa.gov/news-release/us-winter-outlook-warmer-and-drier-south-wetter-north Treatment of damage to both trees by fire and frost is often the same. Wait. Wait for the tree to tell you the extent of the damage. If it's a young tree with mainly green tissue, it becomes apparent pretty soon after the event, within a week to 10 days. With older trees, though it takes longer. With citrus if there is significant damage to the trunk, it's not likely to recover, or recover to commercial status. if it's just damage to the canopy, there's a good chance both trees will recover. If there is damage to the trunk of an avocado, though, it is amazing in its ability to recover. And waiting for up to a year may be necessary to truly evaluate recovery.
Care of Frost/Fire Damaged Trees
Determining the amount of damage is often a difficult job and cannot be done accurately for some months following the freeze. It is usually better to let the tree recover by itself.
Sunburn prevention
Exposed limbs can be badly damaged by sunburning. Whenever defoliated trees have not grown enough new leaves to protect the limbs before hot weather occurs, you should provide protection.
Protection is best provided by spraying or painting all exposed limbs with either a cold-water white latex paint or a whitewash. The paint needs to be white enough to reflect the light, but thin enough to flow through a sprayer. With latex paint, a 2-part latex to 1 part water is usually adequate.
Irrigation
Do not irrigate damaged trees until the soil in the root zone approaches dryness. The loss of leaves reduces the use of water so the soil will remain wet longer than with unaffected trees. Careful, frequent examination of the soil is necessary to prevent excess moisture from normal irrigations. Root Rot occurs in soils with excessive moisture when the Phytophthora fungus is present, and growers must guard against this disease following frost damage. After fire and wind, if soils are dry and there is still green leaves on the canopy, irrigation after the event may be necessary. The key is to check the soil moisture, and if dry, water.
Pruning
Do no prune until you know how much of the tree has been killed. New foliage will grow from the remaining live wood and the tree will recover better without pruning.
When new shoots are at least two or three feet long, you can remove the dead wood. This will usually be mid-summer, 6 to 8 months following the frost/fire event. At the same time, suckers should be thinned out to select the new limbs to replace those lost.
Care of young trees
Badly damaged young trees usually develop strong sucker growth which can be used to form a tree as good as a replanted tree. If these suckers are from above the bud union, you can develop a new top by thinning and training. On young trees damaged to the bud union, strong root suckers can be budded or grafted to the desired variety the following spring. If the sucker growth is weak, the tree should be removed. Trees less than two years of age with only green tissue are usually a lost cause.
Severely damaged mature trees
The handling of severely damaged mature trees where they have been killed back to the large scaffold limbs, to the trunk, or to the ground, presents many problems. Each tree should be considered separately. Often growers can topwork badly frozen trees to a more resistant or productive variety. The hardest thing is to figure out how to treat the range of damage to trees in a single irrigation block - some will need a regular irrigation, some less, and some none at all. Balancing a checker board of trees is difficult.
Two Years After the Fire
avocado burned 2 years later 3
Weed B Gone and Tree B Gone?
With all the rain last year, even extending into August and now with the rains since December there is a lot of natural ground cover growing, When it gets out of hand, we call it weedy. It might still serve the purpose of protecting the ground from erosion, but it can become an impenetrable mess and if allowed to go into summer, a major fire hazard. In the case of some young orchard, the malva and mustard is bigger than the trees themselves. Getting control of them before they get woody and go to seed is easier earlier than later. So it's time to do something about them if you haven't done so already.
A common practice on flat ground is to mow the middles and then weed whack/whip the tree row up to and around the tree trunk. In the case of trees that have their canopies down to the ground or near the ground or that have created a thick leaf mulch, there's not usually much weedy growth near the trunk. Then weed whacking around the canopy is not much of a problem. If on a slope like most avocados, it's a big, expensive, laborious, hot, sweaty, arduous process of weed whacking. Just waiting long enough for the leaf mulch to create a barrier to weed growth and for the canopies to grow out to rob the sun from the surface undergrowth.
In young trees without a large canopy, it can be a really difficult process of getting those weeds near the trunk. Care must be taken to avoid damage to the trunk. In a couple of recent examples, weed whacking got right up and on the trunks and significant damage was done to the trees. When a wound occurs in any tree, a process kicks in to generate tissue to cover the wound, much like what happens with humans and wound cuts. There's a scar left, but it heals over. If the wound is too large, many trees cant cover the woody tissue fast enough. The wood beneath the cambium ( the green tissue below the bark) is prone to fungal infection and eventually the fungus eats away at the interior of the tree. If the wound is large enough and girdles the tree, all the nutrients from the leaves feeding the roots is cut off. The photosynthate sugars that keep the roots functioning, and the roots stop doing what roots do. This is absolutely true is citrus and most other orchard tree crops. But not avocado.
When making a cross section of most trees, it's possible to see the growth rings – the growth increments that appear each year. The tree starts and stops growth each year and it's possible to clearly identified in what year there was more or less growth. In long lived trees like redwood, it's possible to identify years when certain events happened – the year of Lincoln's Gettysburg Address, for example. This growth habit is called ring porous.
In the case of avocado, it has a growth habit called diffuse porous. There is growth throughout the year and the rings are nor clearly delineated, if at all. It's because of this possible active growth occurring, that the avocado can often cover over damage that is quite extensive. After a fire, given time, mature avocado trees can summon up energy to recover to a great extent. It's not so true of young trees, however. Avocados still have a greater regenerative capacity than a lemon tree, and if the damage is to just one side of the tree, there's a very good chance of recovery.
But these young tree are severely impaired. They do have a chance of recovery, but the damage is extensive and the trunk is fully girdled. Only time will tell if they do recover. If the tree were only a year old, it would be a good idea to pull them and start over. But a number of these trees are three years old and have had a lot of investment in them besides their initial nursery cost – pruning, weeding, irrigation, fertilization, etc. It is heart breaking to see damage like this after so much attention has been paid to them.
And the best thing is to let the tree recover on its own. Use of pruning paint actually impairs tissue regeneration. The grower asked if a kaolin protectant like Surround might be used to provide some sun protection. Since that breathes, it might be a good idea. It might also be a good idea to apply some trunk wraps. These were taken off in order to prevent earwig and snail harbor which can cause significant damage to young trees. But they also provide protection from overly aggressive weed whackers. It is always a compromise when making these decisions.
Avocados Get Hot
If you see significant leaf drop in your groves due to excessive heat, the following actions are recommended:
- As soon as possible, whitewash branches exposed to the sun with special attention paid to branches on the west and south sides of the tree.
- Trees that lose a significant portion of leaves cannot efficiently move water, therefore restrict irrigation amounts to ensure you avoid creating wet, soggy conditions that can lead to root rot. It's best to irrigate less frequently and with smaller amounts of water.
- Do not prune your trees — leave hanging leaves in place to protect the tree from sunburn. Once new tree growth has occurred (in the next 3 – 6 months), pruning can take place on living wood.
- Adjust fertilization as you would with a frost-damaged tree: reducing the amount of fertilizer until the tree is re-established. If you see signs of a particular nutrient deficiency, adjust fertilization accordingly.
For more information about managing heat in avocado groves, growers can view the following articles on the California avocado growers' website:
heat damage gem avop
Invasive Goldspotted Borer Hits California Oaks
By Julie Clark, Community Education Specialist III
Goldspotted borer (GSOB) is a beetle invasive to oaks in California. Infestations have ravaged oak woodlands in San Diego and Riverside counties the last 12 years and in Anaheim Hills, Angeles and San Bernardino National Forests the last few years. Preferred hosts are black oak, canyon oak, coast live oak, and occasionally Engelmann oak.
Oak woodlands are highly valued ecosystems that support numerous species of fauna. Oak trees serve as the anchor for these systems and support over 5000 insect species, over 105 bird species, 105 mammal species, 58 species of amphibians and reptiles during their respective life cycles. Many beneficial insects rely on oaks to complete their life cycles and do not damage the trees in doing so.
GSOB bore into the bark of its hosts to lay eggs and rear young. Mature beetles emerge to find new hosts. The adults leave a distinctive D-shape hole in the bark upon exit. 
The insects damage the water and food transfer structures (xylem and phloem) of the tree, causing crown die-back and eventual death in heavily infested (amplifier) trees. Widespread loss of oaks from GSOB has occurred in Idyllwild and San Diego County mountain areas.
Although GSOB are winged, they do not fly long distance. UC researchers, partners with CAL FIRE and the California Firewood Task Force discovered that several of the infestations throughout Southern California were caused by introduction of firewood imported from infestations in other areas. 
D-shaped GSOB exit holes. Credit: UC ANR
Ventura County is vulnerable to attack by the beetle and other invasive tree pests that are on watchlists for the area. Best ways of being assured your firewood is safe include purchasing locally source material or selecting kiln-dried or certified firewood.
For more information:
Report suspected GSOB infestation:
https://ucanr.edu/sites/gsobinfo/What_You_Can_Do/Report_GSOB_Symptoms/
Heat Mitigation Around the World - Avocado
Heat Mitigation Around the World
A chance to hear what can and is being done by growers
to reduce the damage inflicted on avocado fruit and trees
World wide Speakers:
Click here for the June Seminar/Webinar Recording
heat damage to avocado leaves
Heat damaged young avocado fruit
heat damaged young avocdo tree
