Agent Question on Virus Spreading to Next Crop of Strawberries; Key Is Destroying Old Plants NOW (7/3/13)

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In the spirit of proactive communications with our ‘front-line’ extension faculty, I share these questions and replies regarding the virus plant situation that have occurred during the last day.

Happy 4th everyone!

B. Poling


July 2 (1 day ago)

Hi Barclay, 
I am getting several questions from growers regarding planting for fall 2013. They are concerned about plant residue from virus- affected plants in black plastic. 
Their concern is even though they may disc/ plow under, not all plant material will be destroyed. Some are limited in their ability to rotate to a different area because of lack of irrigation. they are asking me: 
1) for guidance as to whether plants are likely to be affected if they are planted in the same fields where virus plants were last year
2) how they can avoid this problem again- is there testing, certification? 
3) They are also asking about compensation- several are not happy with “free plants next year” because they are too worried that they will encounter problems again if they get plants from the same source. 

Can you shed any light on these, so I can share the info with my growers? 

Thanks so much, Nicole Sanchez

Commercial Horticulture Agent

Jones, Craven, Greene, Lenoir and Onslow Counties


Barclay Poling’s reply this morning (July 3):

First, let me address issues re: concerns about spread to fall crop
A. From the attached publication ( 021313 CSJ Strwbry Virus email (1) it is clearly indicated that this virus cannot be transmitted to the next crop of strawberries because this particular virus in strawberry requires an aphid vector to transmit it, and only a few kinds of aphids can do this.  Strawberry aphids, which are members of the genus Chaetosiphon, are necessary for transmission of Strawberry Mild Yellow Edge Virus (SMYEV), and the other virus of concern, Strawberry Mottle Virus (SMoV), is also aphid-transmitted by C. fraegaefolii, several other Chaetosiphon species, as well the melon aphid, Aphis gossypii).
I do not believe that any strawberry aphids are active at this time in summer, and I need to defer to Hannah on the melon aphids.  Nonetheless, by virtue of plowing under and disking in the old strawberry plants, there is not going to be any risk of transmission to the fall crop.  In essence, what your growers need to think about is that by doing this “crop destruct” now, they can 100% remove any risk of infecting the fall crop. 
Summary on Questions Related to Spread of Virus to Next Crop
1)  the really good news is that:  SMYEV and SMoV cannot “infect” any weeds or crop plants other than strawberry (wild and cultivated).
2) Doing a crop destruct now will remove the opportunity for the aphid-vectors (which, are not likely present in July and Aug), to transmit these viruses to the next crop of strawberries, which will not be planted until late Sept/early Oct.  So, we have what the virologist call “time separation.”
3) Finally, there is opportunity for older infected strawberry plants left in the field to infect the wild strawberries, but I am not sure if these are present anywhere nearby the commercial strawberry fields?
In either case, they need to do a crop destruct NOW.
Regarding these questions:
2) how they can avoid this problem again- is there testing, certification? 
3) They are also asking about compensation- several are not happy with “free plants next year” because they are too worried that they will encounter problems again if they get plants from the same source. 
I sent to Dr. Monaco the 2nd article attached  for publication in his Small Fruit Newsletter in July (final version (rev) Poling article Small Fruit news), and the title is “Implementation of a Virus Management Nursery Program in Nova Scotia.” We had a very comprehensive workshop on March 27th, where all the nurseries came to Raleigh, including Balamore, and they all heard Dr. Martin’s presentation which essentially laid the groundwork for a program to prevent this from happening again.  If you read my article, you will see that Balamore has implemented a best management nursery practices program for Virus and this was recommended by D. Martin.  I will be up there July 14-16 to inspect this nursery with Dr. Schnabel at Clemson.  Balamore has just spent about an enormous sum of money on laboratory testing of all their fields (82 acres):
(excerpt from the article)

“…on June 28th a very extensive report that has just come back from the Phyto Diagnostics lab in British Columbia. This is the lab that Balamore has been utilizing since last year to test for both SMoV and SMYEV.  In the June 25th report from Phyto Diagnostics you can see that 234 leaf samples submitted (its and 8-page report), and every leaf sample from all tests were negative for SMYEV for every variety in all of their commercial fields (using Elisa method).  The only positive was a wild berry sample, which they anticipated would be positive. As Joe VanVulpen, Manager, Balamore Farms wrote to me on June 30th, “Very good results.”

(Barclay Poling has this report if anyone is interested, let me know)

Regarding the questions about “free plants having this problem”…I am quite certain that a very rigorous program for virus testing with Phyto Diagnostics will be continued throughout the summer, but one of my questions is when do they plan to test for SMoV, as this report only related to SMYEV.

I am also copying your email to representatives of the nursery, so that they are aware of the kinds of questions that you and I are being asked to field this summer.

This was my conclusion to the article:

Summary – So far, so good! 

    Well, I feel like we have all been on a tremendous learning curve with this new virus challenge facing the North American strawberry nursery and fruit industry. I have personally let go of all my former notions that viruses are not a big concern in eastern strawberry plasticulture. There is way too much at stake for us not to be front and center on this issue!  We have learned from the experts like Dr. Martin what we’re up against, and with the support of Dr. Martin and other researchers like Dr. Ioannis E. Tzanetakis, Dept. of Plant Pathology, Division of Agriculture, University of Arkansas, I am very hopeful that it is possible to develop an effective vector control program for nurseries in Canada, and it appears to me that Balamore Farms is well on its way to turning the corner on this issue.  I know that Dr. Schnabel and I are eagerly looking forward to our July 14-16 visit, and we’ll surely have more information to share with everyone after that trip on the web, but, at this time in early July, I think its fair to say, so far, so good.

Further follow-up from Nicole this afternoon (3:31 pm)

Barclay, thanks for this response. I will be sharing this info with the concerned growers. Happened to just be talking with one of them this afternoon. Two additional questions/ comments resulted. 

1) Grower is asking if lack of root formation on the cuttings is associated with the viruses in question. In his observation, all the plants he got this year, had poor root development, whether they exhibited above ground symptoms or not. He is trying to determine whether the poor root development is a facet of the virus issue, or if there may be something else he needs to be paying attention to. 

2) He is concerned because yes, he has lots of wild strawberry on his property. And to add to that, I can think of two local strawberry farms where I have noticed wild strawberry. I am sure of this because I specifically noted it when I was thinking about SWD and alternative hosts- we know, for instance that SWD can develop in some of our other native plants. So on these farms I was doing a little observation about plants on field edge that might be of concern re SWD, and noticed the wild strawberry. 

Thanks again. I heard that your year would be over in August but I was hoping something could be worked out! You will be missed, but you are right, almighty budget trumps ALL. 

I’ll be looking forward to your response, and have a great holiday weekend…

My reply:

Hi Nicole

I have had a lot of interesting experiences with rooting plugs, and I do not think the lack of root formation is tied to virus situation.  It could be watering, or misting schedules.  Also, temperatures that are really hot are a problem with rooting.  Which town is this grower near?
It might be really good to visit on planting date decisions, as this influences when you plug.  So, I am wondering if you know varieties and what his intentions may be on plant date?
I am very impressed to learn of high wild strawberry population.  I still do not think there is much problem, unless you have seen strawberry aphids this year?  Another question for you!
Thanks for the nice comment about my work here.
Have a great 4th

p.s. your area is not having a preplant meeting?  I am wondering if we could get your growers who may be interested to tune in to webinar on plugging this August 8th


Further comments from Hannah Burrack this evening:

I’d echo Barclay’s comments regarding crop destruct. If the plants are killed, there will be nothing for vectors, even if they were present, to feed on and acquire virus. In field transmission is not our concern–obtaining virus free plants is.
HannahSent from my iPhone
Final Comment – the comment from Hannah, “…obtaining virus free plants is.” Is right on POINT.  Dr. Schnabel and I will be walking the whole 82 acre Balamore nursery the Monday after next (July 15).
Dr. E. Barclay Poling
Professor Emeritus/Extension Strawberry Specialist
Department of Horticultural Science

Campus Box 7609, 162A Kilgore Hall

NC State University
Raleigh, NC 27695-7609
919-418-9687 (Cell)
919-515-2505 (Fax)
Cooperative Extension provides practical education you can trust, to help people, businesses, and communities solve problems, develop skills, and build a better future.

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Photo of Dr. Barclay PolingDr. Barclay PolingFormer Professor and Extension Specialist, Strawberries and Muscadines (919) 515-5373 (Office) barclay_poling@ncsu.eduHorticultural Science - NC State University
Updated on Jul 5, 2013
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