How to distinguish Phytophthora root and crown rot and bacterial canker: video and transcript

In this video Farm Advisor Chuck Ingels distinguishes the symptoms caused by Phytophthora root and crown rot from those caused by bacterial canker in stone fruit orchards.

(Chuck Ingels speaking)

Hi my name is Chuck Ingels, with UC Cooperative Extension in Sacramento County.  Bacterial canker and Phytophthora root and crown rot are two very different diseases.

The reason that bacterial canker and Phytophthora root and crown rot are likely confused is that they both cause bark cankers. See the cankers along these branches? You’ll know they’re not caused by Phytophthora root and crown rot since those cankers are confined to the lower trunk.

What we see here is characteristic small leaves, weakly attached, and the leaves are somewhat yellow.

You can see a bit of oozing around this twig canker. To confirm bacterial canker I’ll cut away at its outer bark to see if it has characteristic red flecks or streaking on the inner bark or sapwood. And bacterial canker, much like fireblight, has a distinct fermented or a sour kind of a smell.

The time when bacterial canker can resemble the symptoms of Phytophthora root and crown rot are when the infection of the bacteria occurs in the trunk. There was a branch here at one point that looked similar to this one or this one that died and the bacteria went into the trunk.

So the entire tree looks like it’s collapsing. With Phytophthora root and crown rot we are going to see the canker on the crown below ground, and that is, the trunk and large roots below ground. And whenever an infection occurs at that point, the entire tree collapses, which we’re seeing here.  There are small leaves, very little growth on the ends, and some yellowing. Now a lot of times we do see with Phytophthora root and crown rot a reddish [color] in the leaves, dull green, reddish, or purplish. Now I’m going to dig on this tree and try to find Phytophthora canker below ground. So we can use the shovel actually.

It looks good down to this point and there’s our margin and then the dead tissue and there’s a distinct margin where the canker has stopped moving upward because the tissues are dry above that point.

And that about covers it. So when you’re out in your orchard and see canker, symptoms will help you determine if you have Phytophthora root and crown rot or bacterial canker.

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