Does anyone have thoughts about what might cause this? I'm only seeing it on one of the three in-ground avocado trees in my greenhouse:
The two main factors to consider are:
- that it's planted next to the outside wall, and the ground there might be a little saturated because the rain barrel overflow is just outside the greenhouse on that side
- that corner of the greenhouse was where the previous owner of our house stored fertilizer and lawn care chemicals, when this was a dirt-floor garage
Soil moisture readings have not shown excessive sogginess, but I'm not sure if the tree sent roots out under the foundation wall, where the ground is definitely more soggy. I'm a little worried this looks like
Phytophthora, especially since right outside this greenhouse I've got a large California bay laurel (Umbellularia californica), which is a species that is often an asymptomatic host of
P. cinnamoni.
I did not see any signs of leaked fertilizer or herbicide before we converted the garage to a greenhouse, but it had been a garage for 70 years, so who knows what might be lurking in the soil.
Here's the full tree, which is showing mild versions of the same symptoms on the rootstock branches (left side), Jade branches (top-right), and on the smaller "Walter Hole" graft (bottom-right):