Hi

I'm studying to be an arborist...i'm not certified but here are a few points for thought....
picture one- extreme marginal leaf necrosis (aka. death from the outside/tip)
picture two- black mold on leaf underside due to high moisture in warmer winter climates, very common this time of year and usually frequent on dead leaves, the black mold is just a result of the leaf necrosis- which is the symptom of the main issue here
Since you just bought the house I'm sure you don't have much history on the property but... was the tree in this condition when you purchased or has it changed drastically since you moved in? If it is recent, then what has changed since you moved in...weather-any really cold or freezing temps after a big rain? have you fertilized/added herbicide to the tree or surrounding areas? any construction that would have damaged the tree roots maybe with a large truck too close?

There are many things that can cause leaf necrosis- (marginal leaf necrosis in this case)...
1. water deficit- most likely not the case based upon this time of year, unless you have noticed leaf wilting prior to the necrosis; also the presence of black mildew on leaf undersides indicates high moisture and is very common this time of year in warmer climates. Black mildew is common when there is too much moisture, this usually subsides as the sun dries everything out and I wouldn't recommend doing much about it. In the winter to help combat mildew and keep it at bay- don't overwater, do not ever water at night-it's too cold for tropicals like avocado and is when bugs/pests thrive and they like water, water to the tree/plant base-keeping the leaves dry!!!, remove old leaf litter-a little mulch is good, but don't suffocate plants/trees in rotting leaves that hold bugs and disease
2. Salt, ion, or Herbicide toxicity....you might want to check with the previous owner to see if the tree was sprayed or any chemicals were added for any reason. The picture you posted looks very similar to herbicide toxicity in the books I am studying!!
3. Severe micronutirent deficiency
4. Air pollution
5. High or low temperatures- avocado is a tropical tree, if the temperatures have dropped suddenly, especially with rain, the tree may just be suffering during the cold winter months and with weather fluctuations
6.excessive sun exposure- avocado trees are sensitive to ozone, so if you had a cold night and it rained and then the next day was hot, the tree may have gotten scorched from uv if the leaves were wet and vulnerable

based on the pictures it appears that it was a quick event that caused the problem, are the leaves on the entire tree like this or is there places where it is more or less damaged?

let me know what you think-if you have any more info that could help and maybe we can come up with an educated guess, if you are concerned about the tree and want to contact a certified arborist in your area to visit
you can search the international society of arborists @
www.isa.org and find a certified one in your area
hope this helps have a great day
:) Danielle
Firegurl

The marginal drying is indeed due to a water shortage.

But commonly for ground-grown avocados in your region, the reason for the water shortage is poor root function due to avocado root rot.

If that's true for your tree, the tree may be able to limp along for a number of years, providing plenty of fruits along the way. Only time will tell.

No treatment will work other than cautious water management -- neither too much, nor too little.

Jean
who previously gardened in Long Beach, CA, for 30-some years

thanks for the info. i don't have any history going back further than november of last year. the tree was in this condition when i bought the house, so i don't think it's anything i've done. it was a bank owned, and the grass was all completely gone, so i would assume nothing was watered for months.

it has been wet her recently, and also hot every other day, with some cold nights.

so i wonder if there was a lack of water, and then i came along and watered it a bunch because i thought it needed it, and then we've had big climate changes. the whole tree is like this.

if it is root rot, can a tree come back from that? i mean, if i water it properly, can the roots fix themselves?

thanks.