miyami, it does look like Gummosis to me, which is Foot Rot caused by Phytophthora. You might be able to save your tree, but this looks pretty extensive, sadly. There are treatments you can apply to the trunk to save the tree. Copper based fungicides applied to the trunk, Ridomil Gold applied to the soil as a soil drench (expensive, and hard to find, as it's commercial, but it is treatment of choice). The feeder roots are at the edge of the canopy, don't worry about what you're seeing by digging around the trunk. No, yellow leaves are not normal and have zero to do with our wonderful California sunshine - that should make your leaves green, not yellow :-) Your tree is seriously underfed, and is in need of regular fertilizing at the canopy edge (dripline) of your tree. Use a good quality citrus fertilizer that contains micronutrients. Also, I can't see because your photos are too little, but it looks? like your tree has algae growing on the trunk? That would make me suspect it is getting hit by sprinkers? If so, this is why you are getting a fungal infection on the trunk. Citrus do not like to get hit by sprinklers. You should be drip watering the tree, with 1 to 3 deep waterings a week, depending upon how hot it is (more in the heat of our summers). And, any grass under the tree should be removed, as grass will compete seriously for nutrients, and cause your tree to become nitrogen-deficient (hence the chlorotic appearance). Water is the culprit here. Too much of it, and in the wrong places.

Patty S.

Here is a link that might be useful: UC IPM: Gummosis

Thanks very much, Patty.

I had Gummosis on the list, but thought it must be something else, since there was no gum like oozing and the open wood would be darker as I understand it.
Given your recommendations about expensive treatments, the stadium of the disease, and that the tree is only 3 years old, it sounds like a logical way to go would just replace the tree with a new one ??

About the fertilizer, I do apply slow release fertilizer and fertilizer spikes, but obviously not frequently enough. My other citrus trees that grow in pots look kind of the same.
What kind of fertilizer would you suggest, and how often to apply?

The tree is drip irrigated but has lots of other plants growing bellow it (grass, some vegetables). I guess I have to change that too.

Could this whole over watering also be caused by not well draining soil, and are there any tricks to mitigate this???

Miyami

Ditch the fertilizer spikes, they really don't work. Fertilize 4 time a year with a good quality citrus fertilizer that contains micros as well as the macros (NPK). And yes, this could be caused by your soil. If you have clay soil, that does not drain well, you're going to have to adjust your watering so that your tree has time to dry out a bit. From your photos, the soil looks very wet, but can't tell for sure. Usually, if you've got clay soil, it is recommended to plant citrus in an elevated manner, on a mound, to assist with drainage, and then make sure you don't over water. My concern is how badly damaged the cambium layer might be on that side of the tree. If it is badly damaged, then it might be worth replacing the tree. I can't see the location well, because the photo is too small, but I would make sure you've got a nice open area, free from grass and receiving full sun.

Patty S.

Hi Patty,

yes, the soil was pretty wet, since it rained (surprisingly) a week before the photo was taken. The bark is completely gone on the affected side, just bare wood. Is the bulging of the scion at the graft caused by the fact that the tri-foliage orange root stock did not grow anymore after the infection?

Here is a larger photo of where the tree grows.
Miyami

Well, you're not helping it any by leaving so much mature fruit on the tree. To my semi-trained eye, it looks almost like critter damage, as if something ate away the bark.
Anyway, I don't like the tree; and if it were mine, I would replace it. The imbalance/overgrowth of the scion relative to the rootstock indicates serious problems. Of course, if it were my Eureka, it would be replaced by a Meyer; once you experience the Meyer, suddenly no other lemon is good enough for you.

My thought is graft failure.