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

too small a pic.. and not enough detail for me to see anything but some kind of mechanical injury ... and would like to see the greater whole.. to see if there is a pattern.. because i see a bunch with no injury.. and two with injury ... any drunken frat parties in the last 6 to 8 months ... which leads me.. somehow.. lol .. to when the actual injury occurred.. rather than when you noticed it ... any kids in the area?? ken

Moisture meters are cheap...and very good. If the topsoil looks dry...it may be plenty wet below. Since this is not a real aggressive growing plant yet....it is not using that much water. I would bet it is not too dry. Don't get fooled, because avos do not like real wet soil (mucky). Also, you may not be getting enough UV's. Are you sure that window is not "low E" glass? Most modern window glass filter out much of the uv rays. Do you have a well-drained potting mix in your pot?

Currently, it is getting half a gallon of water every other day. ===>>> does it need that much.. that often ... are you guessing.. or inserting your finger and finding out.. it its actually near drying in between heavy watering ... how long has it been in the pot.. and that media... such wears out ... and can be a reason... it needs so much water ... so.. i am thinking a water management problem.. is stressing the plant... and once you have a stressed plant .. all kinds of things can overlay that basic issue ... but if you solve those.. w/o addressing such .. you dont end up winning ... i cant recall offhand.. what forum used to carry a heavy load of A questions ... fruit.. houseplant.. or tropical fruit ... you might want to peruse around them ... ken