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

Blowout Beginning for Botrytis Trial

Those of you familiar with my program of research and extension are aware of my rising interest in developing a protocol for consistent treatment separation in Botrytis gray mold fungicide work.  More often that not in the years past, we ended up doing all of the spray and evaluation work just to end up with data with no significant differences, even between the untreated check and the grower standard.  This is a widely known issue in the strawberry researcher community, but so far with little progress on ameliorating it, apparently.

I certainly haven't been idle in this quarter, and have tried larger plot sizes, longer intervals between fruit harvest and even last year putting misters in the plots to soak the flowers and fruit before sunset for the long period of free moisture necessary for development of this disease.  All to no avail, and significant treatment differences were still elusive and rarely found.

On reviewing the literature this past winter, I did find that California Botrytis trials running early in the year, like in March and April, tended to pick up differences in treatment from time to time.  That was the only signal I needed to arm up my spray gear and give it a shot.

As noted in a previous post, my colleagues at PSI and I initiated the first spray application on March 19 before a fairly decent rainstorm (1/2", that counts - CIMIS station # 111 is about 100' away, so it's an accurate number), and proceeded to do the same two more times ahead of subsequent rains and showers (see Slide 1 below,).  The goal of course is to protect the developing fruit and critically the flowers for the periods of free moisture propitious for development of gray mold disease.

Harvest began two weeks ago, and along with picking marketable fruit, cull fruit and evaluating Botrytis in the field, the crew keeps a subset of the marketable fruit for me to take to the lab for clinical evaluation.  The clinical evaluation is done as per the protocol developed by former UCCE plant pathologist Steven Koike, meaning holding the fruit at room temperature and looking for signs of Botrytis infection in the days that follow.

As you can see in slide 2 below, the clinical results are very, very solid.  The untreated control is very much more infected than the grower standard ( 2 applications of Switch, followed by 2 applications of Captan) and the biologicals and a special type of oil are somewhere in between.

Very encouraging results here at the start of the work. I'll reach a bit and think we could be on our way to uncovering the path to a consistent screen of Botrytis fungicides in strawberry.

Slide 1: Rain data from CIMIS station #111 for March and April 2019.  Red arrows mark spray dates.
Slide 1: Rain data from CIMIS station #111 for March and April 2019. Red arrows mark spray dates.

Botrytis clinical evaluation #2 for the 2019 campaign.
Botrytis clinical evaluation #2 for the 2019 campaign.

Botrytis on strawberry.  Note that fruit here is substantially smaller than the fruit in our 2019 study.
Botrytis on strawberry. Note that fruit here is substantially smaller than the fruit in our 2019 study.

Posted on Thursday, April 25, 2019 at 1:08 PM

Comments:

1.
1.) The hand holding the fruit is dirty. It is always a good sign when a researcher's hands are dirty.  
2.) I would have identified the damage to the middle fruit in the photo as damage from sitting in water. This is similar to the damage from sunburn. Fungicides will not control this. Is it botrytis damage?

Posted by Thom Flewell on April 28, 2019 at 7:50 AM

2.
This is a file photo Thom, so the fruit is probably Selva or even earlier. In turn, the hand is not mine, but mine too tend to be dirty, but not all the time. In particular during mealtimes and when going to bed.  
 
Good point on the middle fruit, I sort of wondered about that one myself. If I pushed on it and it was soft, I'd start to lean on the Botrytis call (or if it was REAL soft we'd go further and put it in the soft rot Mucor Rhizopus camp), especially if it was right up against the fruit shown on the left.  
 
Just an FYI, I'm still doing Botrytis reads out of this trial, and just killing it on treatment separation. Stay tuned all.  
 
Thanks Thom for the comment!

Posted by Mark Bolda on April 29, 2019 at 12:35 PM

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