Well after several years of bringing my two Meyers lemons and a key lime tree indoors in the fall, I thought I had the dropping leaves thing licked. Lost very few leaves last fall, and all of the plants did very well during the winter months, blooming and putting on some new growth. The only thing I had been doing different is watering more frequently, on a 2-3 day schedule. More frequent than recommended in many places but it seemed to be working for 4+ months.

In fact all was well until about 6 weeks ago. At that point I started to see more mottled yellow spots on the leaves which continue to grow until the leaf falls off. I always get some of this indoors, and expected it to go away as more light and higher temps started in the spring. However instead of stopping, the problem has gotten worse. Both the Meyers have lost more than 50% of their leaves, and I am not seeing any new leaf growth to speak of. It appears to affect both new and old leaves, and is rather evenly spread over the trees. The lime is less affected but is also loosing leaves.

I am at a loss to figure out what could be causing this problem. My watering schedule has not changed from the previous months. I do not see any signs of mites or other insects infestations. Possibly something eating the roots?

Any suggestions as to where to look or how to diagnose this?

TIA

It could be a simple winter leave drop (seach for WLD) or the very dangerous Phytophthora (search for it).
Look at the root and send us a picture.

I've had seedlings mysteriously die. The leaves turn brown and fall off, then the branches and trunk dry up starting from the top first and it slowly goes down to the soil level. I replant in clean pots and medium but it doesn't help. Is this phytophthora? Is there a treatment?

If it is on small seedlings it can be other fongus but on grown ones it is (nearly) for sure the phytophthora.
Only one way to get off of it: Aliette.

Thank you Sylvain

Only problem now is where to get the Aliette? I looked on ebay, amazon and google, but no luck.

You can look for Fosétyl-Aluminium.

In the first place watering every 2-3 days was not a realistic method to try to prevent any unknown problem from happening, let alone WLD leaf drop which is not a problem connected to the amount of water.. Also if the growth medium that the trees were growing in had good draining, then the excess watering also probably did not cause a problem. It could be phytophthora, but it could also very easily not be phytophthora. Without seeing your tree, I would bet on the side that it is not phytophthora. If you are growing indoor container citrus trees, you should ALWAYS have a soil thermometer -- ALWAYS. Without a soil thermometer your trees are forever in the potential of WLD every winter. You can very easily see if the problem is phytophthora in just 25 - 30 seconds by simply removing the tree from container and inspecting the root system. This should be done before you make any unknown determination, then going around trying to purchase products to cure problems that might not even exist. Indeed the trees problem is either phytophthora or WLD, or simply just old citrus leaves (this is the time of year that old leaves commonly begin to fall, but normally this happens in combination with new leaf production.). - Millet

I did some research on phytophthora. There are no signs of rot up above the soil line, on the trunk or near by. However it could very likely be phytophthora or some other fungus/rot, as with the more frequent watering schedule I was on, the soil did not dry appreciably between waterings. Never got as light as it used to when I was on a once a week water schedule.

So my question is, do I need to go to the heavy guns fungicide, or might some other changes work as well here? Things like letting the soil dry out, using copper based fungicides as a soil drench, or other things.

And, if it comes down to it, where can I get Aliette in small quantities (like enough for three potted trees)?

If there is not any root rot, then you do not need to treat the tree for a root rot problem, and fungicides are not needed. Did you inspect the root system? - Millet

Millet, I wasn't doing the more frequent watering specifically for leaf loss, rather I was attempting to find the right watering pattern. The every 2-3 days kept the top of the soil at approximately the right moisture, just starting to dry at the next watering. And the trees were doing well.

I'll pull a tree and inspect the roots, and post some pics.

As Millet said the right way to go is first make a diagnosis.
Take your plant out of the pot and take a picture of the roots. You don't have to 'brake' the dirt.

Indeed you just want to use chemicals when you have to.

OK, finally pulled one of the lemons and took a look at the roots. Here are some pics, both of the entire tree and just a small piece of root which came off.

One odd thing I noticed is that it was quite hard to pull the root ball from the pot, even though I had not watered for 4+ days. And when I did, the top 2/3 of the soil was dry but the bottom third was still quite wet and did not come out with the rest of the root ball. I thought I had well draining soil mix here, but maybe not.

I cannot tell if the roots are normal or not (never really looked at them much), so if folks would offer a diagnosis I would appreciate it.

The tree's root system looks very healthy. The problem was more than likely WLD. To avoid WLD keep the root system between 64 to 70-F, or keep the tree's foliage out of the direct rays of the sun. During the winter months if the tree is setting in the sun's rays, be sure that both the foliage AND the container are receiving equal amount of the sun's rays. If you purchase a soil thermometer so you can check the temperature of the root system, keeping it at a minimum of 64-F, or better at 70-F your tree will never have a leaf loss from WLD. Because of watering, and evaporation the growth medium will have a lower temperature than the room temperature, so don't rely on he room temperature. Your tree should have a good future. - Millet
'

Thanks Millet, good to hear that the roots look healthy.

I am concerned that two of the trees (both Meyers Lemons) do not have any new leaf growth to speak of. The Key Lime however is putting on new leaf/stem growth. Any other reasons why the lemons would not be growing some new leaves?

Steve, without seeing a picture of the lemon's foliage, it is impossible to make a recommendation, as to why the tree is not putting out new foliage. - Millet