These photos are from an almond orchard with standing water levels about two feet deep for several days due to a problem with drainage. The result this spring are trees that look like this:

Scion death with resprouting from the rootstock. Click to enlarge. Photo: D. Lightle.

In most of these trees, the scion has died (or is dying) and the rootstock (Krymsk 86) is undamaged and resprouting. Gumming was visible on the scion and cutting away the bark revealed cankered wood.

Cankered wood is visible when cutting away the bark at the site of the gumming (red arrow). Click to enlarge. Photo: D. Lightle.

My initial thought was that this may be aerial phytophthora infections resulting from the sustained standing water. During a conversation with Franz Niederholzer, I discovered he had also visited an orchard with very similar symptoms and his initial thought was bacterial canker. We agreed we may have each jumped to conclusions as to the pathogen involved but the end cause and result is the same: sustained standing water in these orchards led to infections and scion death. The growers will need to replant the trees and improve drainage for future seasons.

This entire corner of the field had water approximately 2 feet high for several days following heavy rainstorms. Nearly every tree was affected. Photo: D. Lightle