Photo by Keith TysonI don't usually work with strawberries, but more and more of the farmers, organic and conventional, that I do work with are diversifying into strawberries. Thus, when I saw these notices from our strawberry specialist, Dr. Barclay Poling, I thought it was important to pass them on to you. There are two notices here. The last one concerns organic growers.
October 7, 2009:
1) Phytophthora cactorum (Pc) has been identified in some Canadian (strawberry) plants and an agent in SC has reported this problem in plugs from 2 NC sources last evening. Growers in VA, NC and GA with infected stocks of Camarosa fresh dugs are replacing these plants with ‘cutoffs’ from northern CA. Cutoffs are being shipped now. Digging of CA cutoffs was slightly delayed (by about 1 week) due to lower than normal chilling hour accumulations in Northern CA in late Sept.
2) In certain areas (e.g. Arkansas, WNC and Tidewater VA) wet field conditions plagued growers during the bed-making and pre-plant fumigation, and any further delays in planting will be of critical concern, especially for Camarosa variety. Cutoffs from Northern CA would appear to be the best option at this stage for growers needing to replace Pc infected stocks of Camarosa fresh dugs without incurring additional plant costs. Plugs establish quickly, but virtually no Camarosa plug supplies are left at this time. Alternative suppliers of Camarosa fresh dugs may also be pursued by the grower. Check out NCSA’s PLANT SALES BULLETIN BORAD this morning at http://www.ncstrawberry.org/B_S-plants.cfm. I noted there are Chandler plugs being offered at the moment by 2 NC growers.
3) Growers may wish to consider the option of a phosphite pre-plant dip for cutoffs being set in fields previously planted with Pc infected fresh dugs in late Sept/early Oct, or that have had a previous history of Pc in the soil. Phosphite recommendations found on p.2 of 2009 Strawberry IPM document on www.smallfruits.org (revisions to this document for 2010 have been made, but the phosphite information remains unchanged).
4) It is not advisable to set cutoffs or plugs in the same planting hole as where a Pc infected fresh dug had been previously set – better idea to re-punch new holes in plastic bed
5) Growers are being “strongly advised” against using Ridomil Gold on Strawberry Plugs and would advise growers not to purchase plants from nurserymen who had violated the label that clearly states that this product is not to be used in nursery settings (under the resistance management section). Nurserymen use of Ridomil Gold can lead to resistance issues. The industry cannot afford to have Ridomil Gold become useless in commercial fruit plantings! Appreciation to Dr. Powell Smith, Clemson for providing these important reminders!
6) For Phytophthora and Pythium crown/root rots, mefenoxam (Ridomil Gold EC) is recommended for drip injection in sufficient water to move the fungicide into the root zone. Use proportionately less Ridomil Gold EC for band treatments (e.g., for drip applications). There is question about whether it is best as a pre-plant or post-plant treatment. Consult yesterday's morning advisory (10/5, 11 am) on how some growers use Ridomil Gold as a post-plant treatment.
7) Would this be a good time to re-visit the whole question, “Why didn’t we see this coming?” There are also important dimensions of this Pc problem that impact organic growers in a very serious way!
*Appreciation is expressed to Dr. Powell Smith, Clemson, for his contribution to this advisory (Point No. 5)and to Clemson CES Agent Andy Rollins (Point No. 1).
October 6, 2009:
Dear Growers and Agents -
Please realize that we are dealing with a pretty "dynamic" situation with Phytophthora cactorum, and based on the calls and emails I have received since 11 am, I felt it would be helpful to clarify the current situation as best I can at the end of the day (10/5/09) with points below (5 points). Then, this advisory concludes with more questions that have come in in just the last few minutes (answers will be forthcoming - where possible).
No. 1. Problems with fresh dugs - limited to an Ontario nursery
Unfortunately, some Camarosa fresh dugs from Ghesquiere Farms nursery in Simcoe, Ontario, have been found to be infected with Phytophthora cactorum. I am aware of one distributor for these plants who is taking action to get these replaced with cutoffs from California. I am not aware of any issues with the cutoffs from California. These cutoffs may be shipped a little later than planned as northern CA nursery areas have not had as much chilling in late Sept as usual. I just spoke with Cal Schiemann, Agent, VA-Beach, and he confirmed that one of his largest growers in Virginia Beach, who had problems with Camarosa fresh dugs, is getting replacement cutoffs.
No. 2. Some tips from PEI diagnosed with Phytophthora cactorum, but this appears to be a limited situation.
I am not aware of any Phytophthora cactorum issues with fresh dugs coming from PEI. And, all reports that I have had today indicate that these fresh dugs are establishing very nicely. As reported this morning, there have been some tips from PEI diagnosed with Phytophthora cactorum by NCSU PDIC, but this appears to only be a limited problem at this time. These affected growers are getting direct assistance from their agents, regional agronomists and plant pathologists at NCSU.
No. 3. Precautions Needed In Wet Year.
As I also stated this morning, it would seem that PEI has had another “wet growing season,” and from that standpoint, a Ridomil drip injection would seem to be a good precaution, especially in this wet year we are also having in the Mid-South. Also, Sweet Charlie is especially susceptible to Phytophthora cactorum.
No. 4. Please note that Ridomil Gold is only being recommended for drip injection.
Remember, it is important to do drip injection of Ridomil Gold and NOT to apply as a foliar spray
No. 5. What can be done if you are an organic grower?
Thats' a tough one. Earlier today Sue Colluci wrote: "Dear Dr. Poling and Dr. Louws, Is there anything an organic grower to do if they suspect Phytophtora after they have planted? For future recommendations, would you advise a grower to treat plugs with Oxidate and possibly use something like Mycostop? What about copper products? Any advice would be helpful!
Dr. Frank Louws answered:
I could not offer much information for an organic system with an established problem. The key will be to limit excess moisture - ensure optimum drainage of beds and between beds; do not let water collect in headlands or in the field. Oxidate has not performed well in our trials. I could envision that it would help to reduce any inoculum on the foliage (contact efficacy) for Botrytis. anthracnose and Xanthomonas (bacterial angular leaf spot) and Powdery mildew etc. Mycostop is a good idea - it could help; we also had success with Trichoderma (e.g. T-22 and other formulations for suppressing root rot pressure in the plug production phase. I would pro-actively incorporate these products into the plug mixture prior to plugging with a follow-up application in week 3 or so. We did a lot of this type of work with some success (i.e. better than nothing). This is not encouraging overall , but that is the state of things as I understand them. I have seen high risk plants (with known levels of Phytophthora) go into an organic system with less than predicted losses - so that was encouraging. Copper could suppress foliage based pathogens about 30% (compared to e.g. 90% for a selected fungicide). I am unsure about copper phytotoxicity in the plug production phase. I have not seen serious issues in the field production phase in NC. hHowever, we are conservative about its use during flowering and fruiting. These are thoughts from my experience. Ensuring disease free plants is the most important tool for our organic growers complemented with healthy soil systems, a systematic rotation plan and a clean water source.
Thanks for the great question." FJL