Environ. Horticulture, Pears, Cherries, and Viticulture
University of California
Environ. Horticulture, Pears, Cherries, and Viticulture

Comparing Phytotoxicity Damage with Zythia

I have a pretty unique opportunity going right now in one my test plots.  The plot has a fairly decent run of Zythia going, at the same time one of the test materials is causing a slight burn on the leaves (it's an unregistered oil), so we have the chance to compare the two.

Those of you have called me concerning Zythia know that I look for the little brown to black spots representing fruiting bodies (thank you Steven Koike!) in the centers of the necrotic areas caused by the fungus to confirm it.  Usually there are concentric rings of growth also, and while these aren't diagnostic they for sure point out that symptom in question is being caused by a living organism.

Contrast that with phytotoxic burn of the leaves and other plant parts.  No fruiting bodies for sure, nor any rings of growth.  Too, if one is familiar with how spray droplets disperse on the leaves, it should be a small matter to trace back areas of burn to where water would gather.  Veins, edges of leaves and low spots on the foliage are common.

Let's go to the pictures to make my point, shall we? 

View from the top, distinct areas of tan colored burns distributed around the most exposed leaves.
View from the top, distinct areas of tan colored burns distributed around the most exposed leaves.

Spray burn close up.  Distinct tan area at leaf edge.
Spray burn close up. Distinct tan area at leaf edge.

Leaf severly infected with Zythia fungus.  Note the abundance of dark colored fruiting bodies towards the center of the spot.
Leaf severly infected with Zythia fungus. Note the abundance of dark colored fruiting bodies towards the center of the spot.

Comparing phyto burn (leaf on the left) with Zythia (leaf on the right).
Comparing phyto burn (leaf on the left) with Zythia (leaf on the right).

Challenge question.  Which one is the phyto?  Spoiler alert - the answer is now in the comments below.
Challenge question. Which one is the phyto? Spoiler alert - the answer is now in the comments below.

Posted on Wednesday, April 10, 2019 at 12:39 PM

Comments:

1.
Left is Zythia and right side is Phyto....?

Posted by Juan C Muniz on April 11, 2019 at 4:00 PM

2.
Ok Juan. Can you tell me your reason for thinking so? Getting others taking a shot at this one too.  
Mark

Posted by Mark Bolda on April 11, 2019 at 5:46 PM

3.
Two main reasons:  
 
1) The right hand side (which I think is Phyto) is lighter brown and seems to have damage starting on the edge and lower area on the leaf and moving inward which would indicate the spray product.  
 
2) The left hand side (which I think is Zytnia) is darker brown and randomly appears randomly on the leaf.

Posted by Juan C Muniz on April 12, 2019 at 8:21 AM

4.
And the other thing is Juan, if you blow the picture up pretty good, you can see a few distinct dark colored dots that very likely are the fruiting bodies of Zythia. Nice work my man.  
Now I'll have to put a "spoiler alert" on the photo caption so people know the answer is here.  
Mark

Posted by Mark Bolda on April 12, 2019 at 1:57 PM

5.
Mark, your posts are always very helpful to me and I am sure they are to many others as well...keep up the good work!

Posted by Juan C Muniz on April 12, 2019 at 3:20 PM

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