Strawberries

Water Damage in Strawberry

The rain on Saturday (about 0.6" total by my gauge), did present a setback for area strawberry growers.  Not too much, but still damage has been evident, it is worth noting that that for many varieties grown on the Central Coast water accumulation over 0.5" inches means damage for mature fruit.

I happened across the damage pictured below on my wanderings through the fields last week, and it occurred to me it might be interesting to investigate why we get this cracking of the mature fruit.  I tended to think fruit would crack because, confronted with more water than necessary from the rain, the plant to which the fruit is attached is forced to pull up more water than usual, inflating it faster than it can bear and leading to cracks.

This former thinking of mine is totally wrong.  As outlined in the super informative work published in the paper linked below, the story of fruit cracking in strawberry is rather all about osmosis, which as most of you know is the process by which water passes from a solution of a lower concentration of dissolved materials into one of a higher concentration of dissolved materials.  Meaning that rain, being essentially pure water with almost nothing dissolved in it, landing on a mature strawberry fruit loaded with solutes (mostly sugars), is going to get pulled pretty effectively by osmosis into the fruit, swelling the areas under the raindrops beyond the capacity to stretch and form cracks. Carrying this logic of osmotic potential forward also explains why less mature fruit, with their lower concentrations of solute (sugars), tend to avoid damage in rainstorms.

Very nice thing to learn about today. Full article here:

 

Water Soaking in Berries: Triggers, Factors and Mechanisms

 

 

 

 

 

Bad case of cracking from last Saturday's rainstorm.

More cracking, if you zoom in you can see a vinegar fly on task, already hunting for a site on the damaged fruit to put down a clutch of eggs. All is as it should be.

Damaged strawberry with less mature, undamaged fruit in the hinterground.

Angular Leaf Spot - Time to Worry?

Following the rain of this past week Saturday, we've been hearing about a pretty significant outbreak of angular leaf spot in strawberry.  We include some pictures from a field of Cabrillo taken the morning of May 6.

In the way of review, angular leaf spot in strawberry is caused by the bacterial pathogen Xanthomonas fragariae, and manifests itself as you can see in all the photos below. In particular, the underside of the leaf will take on a watery appearance in vein delimited areas of the leaf (Photo 3), and in often in the morning have a sort of goo there (and it is real sticky, brush your finger over it and you will know, this is the cytoplasm from the lysed plant cells).

Addressing the question: Is this a time to worry?  All things considered, we think probably not, unless it rains again.  What is very likely the cause of this heavier than average outbreak of angular leaf spot this year is the greater frequency of rainstorms, in other words unlike last year with huge intense rains interspersed with longer periods of dry, this year has experienced lighter rains but at more frequent intervals, creating lengthier durations of free moisture on the leaves which has created good growth conditions for Xanthomonas fragariae.  

So if the trend from here on out is dry as it is supposed to be, there is less reason to worry about this outbreak becoming worse and causing trouble.

Angular leaf spot on strawberry, note older leaves with distinctive coloration of various hues.

Close up of angular leaf spot.

Underside of leaf with angular leaf spot, note watery appearance, much of which is delimited by veins.

Agdia Immunostrips for Diagnosing Phytophthora in the Field

The following article is a discussion of Agdia Immunostrips (photo 1 below) for making diagnoses of Phytophthora from plants.

The idea with the strips is sort of what most of us have already experienced with the Covid test kits - basically you get a sample, process it in some way (swirling a Q-tip around in your nostril for Covid or crushing up suspect root tissue with the Agdia test - see photo 2 below) and then you get a result of one or two lines (one the control on top, and a second stripe appearing when you have the disease and no stripe appearing if you don't).  An example of a positive read which was subsequently verified as positive with a highly reputable plant disease diagnostic lab is shown on the third photo below.

Do they work consistently would be the next question, and our own little bit of experience now, together with the experience of other researchers in our industry, says that yes they do.

Last year, the berry industry experienced more than significant amounts of flooding, which presented us with a tremendous opportunity to test these strips for the water loving Phytophthora. Two tests were done side by side with samples submitted to Trical Diagnostics, a local lab recognized for accurate diagnosis of plant diseases.  In this very small sample, one trial out of strawberry tested positive with the Agdia strips also came out positive at Trical Diagnostics for Phytophthora, and another sample which Mark swore up and down would test positive for Phytophthora (very early in the season, cool weather and excessive moisture at the bottom of the hill), did not test positive with the strips and this was substantiated by a diagnosis not of Phytophthora but of Fusarium oxysporum f.sp. fragariae.  

This year, Mark was called out to field suffering a great deal of wilt in raspberries, prompting yet again a test with the Agdia strips, and ALL FIVE samples tested positive for Phytophthora (see photo 5 below), a result which was confirmed by in-house testing by that company's research support of plants from the same field.

The thought is then at this point to share that these testing strips can be useful to the grower in diagnosing Phytophthora and Phytophthora like species.  Since these strips DO NOT diagnose down to the level of species, which while for most field management decisions is ok, those desiring an understanding of a problem down to that level still must do at a reputable plant diagnostic laboratory.

 

 

Photo 1. A package of Agdia test strips, there are 25 strips per tube and together with the bags of buffer cost is a bit over $100.

Photo 2. Suspect root samples laid out ready for insertion into the bags of buffer solution in the hinterground and subsequent maceration.

Photo 3. A positive read of a sample, notice the lighter line 2/3's of the way down the strip, this is an indication of positive.

Photo 4. Five in a row, all positive - later confirmed by grower support research lab as Phytophthora.

Photo 5: One of the Phytophthora affected raspberry plants in the field.

Meeting Announcement-California Berry Cultivars May 7

California Berry Cultivars (CBC)will host a field day in Watsonville on Tuesday, May 7^th starting at 10:30AM.  Content will be solid; along with a presentation and field walk around by CBC staff and a talk on soil disease by Samantha Simard from CalPoly I'll be giving a talk on some findings on cold conditioning in strawberry. A BBQ lunch will be provided afterwards. 

Agenda is attached below; key meeting data is here:

When: May 7^th, at 10:30AM

Where: 181 Dairy Rd, Watsonville, CA

 

Look forward seeing you all there!

Special Seminar: Recent Research Developments on Spotted Wing Drosophila (SWD) Insecticide Resistance in the Monterey Bay Area

Nationally recognized and long time California strawberry entomologist Frank Zalom will join Christine Tabuloc and myself this coming Friday April 19 at my office in Watsonville to discuss recent developments in insecticide resistance in our populations of spotted wing drosophila (SWD).  It's no secret to anybody that these flies have been tougher to control as our insecticides lose efficacy because of resistance; this seminar will give some insight as to how and why this is happening with some thoughts at the end by these entomology leaders on what steps to take next.

Meeting set to start at 9:30 am and continue until noon.  It's a fairly specialized topic, but all are welcome to attend.

More details can be found in the pdf agenda attached below.

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