One can see here from the picture kindly provided by Doug Thomas of Crown Nursery that the cold of late is having an effect. Total accumulation of chill by 10/29 in Macdoel when this picture was taken was 364 hours (this is over 329 one week ago) between the critical temperatures of 33 and 45 degrees, offset by 394 + 123 hours above 60 degrees.
Warm weather has more or less ceased to be a factor here, allowing the chill hours to accumulate much quicker, and it is subsequently showing on the plants.
Thanks to Doug Thomas of Crown Nursery, I'm able to see how the plants are changing as the weather cools up at MacDoel. This is a picture of Monterey close to the field of my original post.
Total chill between 33 and 45 degrees accumulation to this date Oct 23, 2020: 329 hrs, with 372 + 123 hrs over 60 degrees.
In comparison, chill accumulation in this range by Oct 15 was 267 hours, with 324 + 123 hrs over 60 degrees.
In short, warm temps during the day are diminishing rapidly at the same time that chill hours between 33 and 45 are increasing. I think we are seeing that here with some change to the aspect of the plants. This is very good news.
- Author: Lisa DeVetter
- Author: Mark Bolda
Biodegradable plastic mulches (BDMs) are a promising alternative to polyethylene mulch. The concept is simple. Rather than pulling used plastic mulch from a field and stockpiling or disposing it in a landfill, BDMs are designed to be tilled in at the end of the production cycle. Afterwards, soil microorganisms convert BDM fragments into microbial biomass and CO2. Previous research has shown BDM performance in strawberry systems is comparable to PE mulch. Given this, BDMs seem like a sustainable alternative to the current status quo of plastic mulch waste generation and disposal and would be appealing for organic production. However, caution is warranted when considering BDM use in organic systems!
While the USDA National Organic Program (NOP) added biobased BDMs to their list of allowed synthetic substances in 2018, it is important to remember that no commercially available BDMs (with the exception of paper-based films) meet the NOP's criteria for use in certified organic production [7 Code of Federal Regulations, Section 205.601 (USDA 2014)].
To be allowed in organic production, BDMs must:
- Fulfill criteria for being biobased as evaluated using standardized tests such as ASTM D6866.
- Be produced without organisms or feedstock derived from excluded methods (e.g., GMOs) [7 CFR, Section 205.601(b)(2)(iii)].
- Meet compostability specifications of either ASTM D6400, ASTM D6868, European Standards (EN) 13432, EN 14995, or ISO 17088 (7 CFR, Section 205.2).
- Reach at least 90% biodegradation in the soil within two years or less as evaluated using standardized tests such as ISO 17556 or ASTM D5988.
Completely biobased BDMs that are produced without GMOs is difficult and cost-prohibitive at the manufacturing level. Furthermore, biobased content is not correlated with in-soil biodegradability. Research on the application of BDMs in specialty crop systems is certainly warranted and underway. Part of that research will inform questions pertaining to the application of BDMs in organic systems.
If you would like to learn more about BDMs and issues pertaining to organic production, please visit: https://smallfruits.wsu.edu/plastic-mulches/. You can also participate in National Organic Standards Board meetings and vocalize your questions and concerns regarding BDM use in organic systems.
I've been entertaining a fair number of calls from worried growers, farm managers and others in regards to the warmer than normal temperatures this year at the strawberry plant nurseries up in Northern California. Plants will be delayed in entering dormancy in this environment and might not be setting up well (see photo 1 below from October 6; thank you Doug Thomas). The concern is what this is going to translate to in the production fields here on the Central Coast.
For those unfamiliar with the concept of cold conditioning, aka chill, recall that strawberries and caneberries are plants from temperate regions, and rely on enough accumulation of time in certain cold ranges during the winter, most often 28 to 45o F, to develop and produce fruit normally the following season. The field portion of cold conditioning for strawberry concerns itself with entering dormancy, which manifests itself as you would expect with coloring of the leaves and cessation of growth. Not entering into this stage and or having this in insufficiency in strawberry generally results in lower vigor and productivity later on.
Yes, the amount of chill hours for strawberries this year are pretty low in comparison with most others, with the implication that growers will be faced with lowered fruit productivity because of it. At last view on October 15, 2020 in Macdoel, CA, where most of our plants are grown, we had accumulated 267 hours of cold between the critical temperatures of 33-45 o F, where in the previous two years it was already above 300 hours by this date. Then again, looking back to 2017, the chill hours accumulated in this range by October 15 was 257, and most people will say that the fruit production that year was good. However, the catch this year is the abnormal amount of hot weather during the day, which according to several chill accumulation models subtracts from that accumulated at the colder end. Bottom line is that it looks like we are lacking in field cold accumulation this year in comparison to past years.
Obviously to the extent possible, growers should seek to get harvest dates by which time sufficient field chill has been accumulated. However, while delay might be a tactic for a few days, growers need to be aware that prime planting is the first two weeks of November for UC varieties, and pushing out from that just to get higher amounts of chill might not work out so well. Additionally, nurseries aren't necessarily going to delay harvest since it runs the risk of getting into wet weather and the subsequent impossibility of harvesting plants at all.
So what does a grower do to accommodate this situation of low field chill? The supplemental chill, which is the cold storage of the transplants postharvest, can't substitute for the chill accumulated in the field and should not be adjusted one way or the other from that recommended by UC or proprietary breeder guidelines. From the UC side at least, those guidelines come from many years of research, and do represent the optimum storage length across a variety of years and subsequently environmental conditions. The plant at the stage of supplemental chill is not in the same state as it was in the field with all of its leaves, roots in soil and exposed to the daily cycle of light and dark.
I can only underline that close adherence to good planting practices, again available in many places such as the UC IPM guidelines and other sources on California strawberry, will grant benefit to the plant and overcome some of the dearth of vigor we expect from less than normal field chill. Good soil preparation, planting roots straight down rather than J rooting, delaying bed plastic placement, keeping plants moist at all times until planting and afterward with abundant irrigation will enhance plant productivity whatever the case has been in the nurseries.
Let's not be cutting any corners this year folks lest the endeavor end in tears is my thought right now.
- Author: Lisa DeVetter
- Author: Mark Bolda
Biodegradable mulches are a promising alternative to traditional polyethene plastic mulches that reduce plastic waste generation and provide opportunities to reduce the costs of mulch removal and disposal. They are currently being investigated in strawberry systems in collaboration with the University of California Extension, Monterey Bay National Marine Sanctuary, Cal Poly, and Washington State University.
Since we are investigating this technology here in California, look to this blog for occasional developments in research and regulation in soil biodegradable mulches.
The State of California recently set standards for soil biodegradable mulches:
“Biodegradable” is a term that is often associated with environmental stewardship and sustainability. Unfortunately, it is also a descriptor that has been abused and manipulated by plastic manufacturing companies that used it for marketing purposes. This was done by selling materials labeled as “biodegradable”, even though they were not biodegradable and did not meet scientific standards for degradability. An example strawberry growers may be familiar from years past would be oxo-degradable and photo-degradable mulches, which were falsely sold as biodegradable mulches. These mulches are not truly biodegradable, simply fragmented into smaller plastic pieces and that contributed to soil pollution.
Truly sustainable mulch alternatives DO exist and their credibility just got a boost in September 2020 when the California legislature and Governor Newsom legally allowed the term “soil biodegradable” be applied to horticultural mulch films. To ensure the integrity of the product, mulches claiming the “soil biodegradable” label must meet scientific standards for degradability, such as EN 17033:2018 ("Plastics - Biodegradable mulch films for use in agriculture or horticulture - Requirements and test methods"). Equivalent or more stringent standards may also be used in place of EN 17033.
What does this mean for you as a grower in California? It ensures that if you are applying a mulch labeled as “soil biodegradable”, the mulch must meet specific standards of degradability assessed using approved, standardized laboratory tests. This protects the grower from inadvertently applying products that do not meet these standards and accidentally contributing to plastic pollution in soils.
You can learn more about biodegradable mulches at: https://smallfruits.wsu.edu/plastic-mulches/