WHAT: SANTA CRUZ AG DEPARTMENT – CONTINUING EDUCATION CLASS FOR GROWERS AND CERTIFIED PESTICIDE APPLICATORS
WHEN: MONDAY, DECEMBER 9, 2019
9AM – 11AM (ENGLISH) – registration starts at 8AM
2PM – 4PM (ESPAÑOL) – registration starts at 1PM
WHERE: UC COOPERATIVE EXTENSION AUDITORIUM – 1432 FREEDOM BLVD, WATSONVILLE, CA
2 hours of DPR continuing education credit for Laws & Regulations approved. Register when you arrive. There is no fee to attend this class.
The question of organic strawberry transplants is one that has turned through the industry for some time, and the picture has sharpened somewhat since our organic strawberry transplant meeting.
It's clear by now that it is possible to organically produce a transplant of comparable productive capacity to one conventionally produced. We had data at the meeting saying as much presented by Fernando Garcia, formally of FarmFuels and now with ReiterBerry , and I oversaw a similar project three years ago, again supported by Farm Fuels and executed by Anna Brown, with a similar outcome.
I too ran a study a number of years ago in 2003-2004 together with James Rickert and then Farm Advisor Dan Marcum of Butte County comparing three varieties, grown organically and conventionally, and again had little difference between them (figures included below).
So we know now that there is no issue with productive capacity of organic v conventionally produced plants.
But the major issue of phytosanitation still remains. Phytosanitation was acknowledged by the plant growers themselves in their presentations and was the main topic in the later conversations I had with several attendees (thank you) afterwards. Plainly spoken, organic transplants run a higher risk of having disease on them that will reduce yields and contaminate ground. Conventionally produced transplants, by merit of having recourse to more materials to reduce disease, run a lesser chance of having this happen.
Encouragingly, at the meeting we were shown that there is a lot of research seeking a higher assurance of no disease contamination in organic strawberry transplant production, and that is still ongoing.
Again, as we move forward with this project of organic transplants, we need to be clear that the matter at hand right now is not that of plant productivity, but that of reducing risk of loss and contamination of the organically grown transplant. We will hope that the regulatory and agencies overseeing organic production take heed.
As most readers of this blog know, the loss of the pre-plant soil fumigant methyl bromide several years ago presents a serious challenge to business as usual in the California strawberry industry. The search for alternatives, both to the fumigant itself and the practices built up around it over the many decades of its use, has not been an easy one.
Into this fray comes UC Santa Cruz sociologist Julie Guthman with her book Wilted: Pathogens, Chemicals and the Fragile Future of the California Strawberry Industry. She tells the story of how the use of methyl bromide soil fumigation to address soil pathogen problems, from Verticillium earlier, now joined by Fusarium and Macrophomina, has indelibly changed the strawberry industry, from land use patterns, to labor, to publicly supported agricultural science to breeding priorities. In her opinion, the future of our industry has become more tenuous, indeed, in her words is destined to become a landscape of ruin.
To open, the early part of the book really shines and underlines the tremendous amount of research that Dr. Guthman did, as it delves into the history of strawberry culture in California. Beginning from European breeders dabbling with strawberry in the 17th century to the foundation of the California strawberry industry in 1880, then on through the breeding efforts of both the University and private interests (and to be sure, the attendant controversies most of the way), Guthman takes us through a highly interesting tour from the early years of discovery and development to the improvements in productivity, taste and to some extent disease resistance of the modern berry we know today.
As alluded to previously, the book's central argument, built up over several chapters, is the loss of methyl bromide is only the beginning of a fairly dark path forward. She maintains that the strawberry industry in California will cease to be once the chemical fumigants, in particular the chloropicrin which has replaced methyl bromide, become too expensive or are regulated out of existence.
The California strawberry industry, so dependent on fumigants, has been bred for the wrong things and subsequently is not now poised to be particularly resilient to the change foisted upon it by their loss. Breeding has been built around methyl bromide, land use is determined around the ability to fumigate out problems and return to it with little time for rotation and rest, and labor is dependent upon the high yields enabled by fumigation. It all fits together under efficacious fumigation, and will all fall apart without it.
One of the keener aspects of our loss of methyl bromide fumigation has been the emergence of two pathogens, Fusarium wilt and charcoal rot caused by Macrophomina, which has been a question for the scientific community to answer. The author herself wades into this controversy, and floats the idea that epigenetic changes in these two pathogens, that is modification of the expression of the genes rather than the underlying gene code itself, brought on by continual strawberry cultivation and chemical soil fumigation may have resulted in the creation of more virulence and a subsequent emergence as serious pathogens in the strawberry production system.
This view of epigenetic expression resulting in the emergence of these two pathogens, intriguing however it may be, is not well supported by the evidence. A recent paper out of the USDA describes differences in the DNA of the Macrophomina pathogen on strawberry and that of Macrophomina on other hosts. Additionally, the argument that we may have fumigated our way into this problem is significantly undone by strong suggestions that Fusarium was introduced from Japan, where it emerged in the late 1960's - well before fumigation was a widespread practice there.
Dr. Guthman moves on from this survey of what is happening with the loss of fumigation to discuss the alternatives, but is unable to find a suitable fit for replacing what we had with methyl bromide. Anaerobic soil disinfestation (ASD), which is soil flooding with the addition of carbon sources to ultimately create a condition suppressive to pathogens. But since the adoption of ASD by growers in California has been halting, Guthman, along with mentioning an efficacy which often falls short of that of fumigation, underlines that the large amounts of input required, from the amendments themselves to the water to the plastic covering. She also discusses the use of soilless substrates, either in troughs carved out of existing beds or completely soilless systems grown indoors, but again notes the difficulty in this becoming widespread because of cost, technological complexity and necessity of importing inputs.
I believe that Dr. Guthman is not finding the solution she seeks because it cannot be found as a single thing. The answer lies, and I know I am not alone in this view among our scientific community, in a number of practices, not all of them necessarily directed at reducing or resisting soil pathogens, being used together. Developing something this complex takes the input of people from multiple disciplines, and we in the research community, from breeders, to plant pathologists, to pomologists, to growers, both from the public and private sector, have been doing just that for at least the past several years. We don't have the solution yet, but we will get there, I am certain.
A final note is that the book would very much have benefitted from some editing. Errors range from the mundane, such as the incorrect captioning of a picture of recently cut fumigation tarp as being “shredded by the wind”, to the more eye opening such as the unsupported statement of a private sector breeder saying that the UC breeding program under Dr. Shaw and Dr. Larsen did not do disease screens (they did, showed the plots at field days and wrote quite a few papers about them), to the breathtaking such as identifying a REIT (a real estate investment trust, which is a publicly traded company which owns, operates or finances real estate) as a “derivative” such as a futures contract, option, or swap. These sorts of errors tend to undermine one's confidence that the rest of the very well researched story here is true.
Caveats aside, all in all, this new addition to the ever expanding library of commentary on the California strawberry industry is a good one and for those looking for a good detailed description of our industry would be well advised to pick it up and read it.
Lisa Bunin from Organic Advocacy and I have a meeting planned for this upcoming November 25 concerning the use of organic transplants in strawberry. Regulators will be on hand to clarify what the regulations regarding the use of these plants will look like for organic growers going forward. Additionally, a representative from ION, a leading producer of organic planting stock, will be on hand.
Very good meeting concern a topic of great interest to organic growers.
Agenda included below.
- Author: Michael Cahn
- Author: Mark Bolda
Mark here - Mike presented this information at the "Mariscada meeting" held by Gerry Spinelli a couple of weeks ago. Excellent meeting by the way, but with very few people in attendance. One part in particular, this being the necessity of a certain soil N concentration early in the season even though the plant requirements are low since it is small, presented by Mike on nitrogen management of strawberry transplants really caught my attention, so I asked him to write that up for all of us. He graciously offered to do this, and his summary appears here. Thanks Mike!
Nitrogen Management of Strawberry during Establishment and Early Season
Growers follow a number of strategies for managing nitrogen during the early season. Some apply almost half of the seasonal nitrogen required by strawberry as preplant fertilizer before transplanting while others skip preplant fertilizer or use a reduced rate (Fig. 1). Others use controlled release fertilizers while some growers opt for conventional fertilizer products. These decisions are based on grower experience, cultivar, soil type, and anticipated weather conditions. The following are a few concepts on early season N management for strawberry to consider as we enter a new season.
On the central coast the N needs of strawberry are quite modest for the first few months after transplanting. This is because growth rates are low until March when average temperature and day length begin to increase. For most varieties, strawberries will take up 20 to 30 lbs of N/acre during this period. However, new transplants have a very limited root system and need nitrogen to jump start root and shoot growth. A rule of thumb is to have 10 to 15 ppm mineral N (nitrate + ammonium) in the upper foot during the early season, which is equivalent to 35 to 60 lbs N/acre, depending on the soil texture. Usually most of the soil mineral N is in the nitrate form. Checking the soil at least monthly during the early season can help determine if supplemental fertilizer is needed, which can be applied through the drip system.
The decision to use preplant fertilizer may depend on several factors such as anticipated rainfall, soil texture, previous crop, and initial soil nitrate concentration. When following vegetables, the concentration of soil nitrate can be high (20 to 30 ppm NO3-N) and can supply a large portion of the early crop N needs if not leached out by irrigation and rainfall. In contrast, the level of soil nitrate maybe low when planting after a strawberry crop (< 5 ppm NO3-N), and the transplants may need some fertilizer nitrogen to simulate root and shoot growth.
Soil type and anticipated rainfall should also be considered in deciding whether to use preplant fertilizer. Even with plastic mulch, a strawberry crop planted on a sandy soil could lose much of the soil nitrate during heavy rain events. On the other hand, preplant fertilizer may increase salinity near the root system, especially if it is banded near the plant row and rainfall is light during the winter (Fig. 2 below). Controlled released fertilizers are more expensive than conventional fertilizers but can be a good option if soil nitrate is low at transplanting and the release rate of the fertilizer matches the N uptake rate of the crop.
Also consider the nitrogen contribution of other sources of N to the crop. High nitrate irrigation water can supply much of the N needs of the crop in early season, especially during a dry year when the crop is frequently irrigated. Recycled water can also contain a significant amount of nitrogen as both nitrate-N and ammonium-N. More information on how to credit the N in irrigation water can be found in the Salinas Valley Blog. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=7744 Added organic amendments and soil organic matter can also play a role in supplying N, depending on soil temperatures during the winter.
Because there can be several factors that affect soil nitrate levels during the early season, we recommend evaluating the soil nitrate concentration at least once per month and making adjustments by fertigating as needed. This approach provides flexibility so that the reliance on preplant fertilizer can be less without risking crop yield loss. The soil nitrate quick test is an accurate and easy tool to use that can allow growers to monitor soil nitrate. More information on using the soil nitrate test can be found on the Salinas Agriculture Blog. https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=4406
In summary, multiple approaches to N management can work for strawberry because the N demand is low during the early season, and the combination of residual soil nitrate, N mineralization from soil and amendments, and nitrate in the irrigation water can often supply much of the N that the crop needs to become established.