As we creep towards strawberry planting season on the Central Coast, it is always good to review where we stand currently on nursery cold conditioning, and with this in mind, think about adjustments to the post harvest supplementary chill based on what sort of winter we might be expecting.
Those of you who know me understand my faith in hedging my bets and planning for contingencies. I favor decisions with a high probability of success and decent outcomes over swing for the fences with blow your socks off results but missing and failing most of the time. Short supplemental chill times with early planting dates to get the beat on the competition are not my thing since this strategy puts good plant vigor at risk, especially if this 2017-18 winter is warm.
Chill accumulation for this year looks good at the nurseries up at MacDoel. Using Lassen Canyon Nursery's chill accumulation chart (also appreciate the comps to previous years- very useful), shows that, after a warm start in September, hours have really ramped up and currently as of October 5 we are at 337 total hours according to my Utah model calculations (which subtracts chill during warm weather episodes, and discounts temperatures under freezing - look elsewhere on this blog for how I am doing this). That compares very well with previous years, and is in fact ahead of many of them.
Further, looking forward to what sort of winter we are to expect, let's go to the NOAA weather maps. Quite simply, for all of our strawberry production areas, it is as of now 40% probable that we get temperatures above normal this winter (being December, January and February). This is up from 33% a few weeks ago, so I am sensing a trend which seems to confirm where we are headed.
In conclusion, with solid field chill already in the can but a good probability of a warmer than normal winter in the offing, I would again this year favor just a little bit more supplemental chill than customary.
Nobody can say we shouldn't have seen this coming.
In the current NAFTA renegotiation, the thriving berry industry (88,000 acres representing a fivefold increase in one decade to 1.26 billion dollars in sales) of central Mexico has come into focus as an unfair competitor to US growers, enjoying cheap labor, state subsidies and year round growing conditions.
Interesting to see also the differences in attitude on this question between large growers, who operate in all three NAFTA signatories, and small growers who produce only domestically.
Good article, paywall protected though.
Attached is the latest iteration of the grower guidelines a number of us at UC Cooperative Extension have written and have had published by the California Strawberry Commission.
Super timely since planting is right around the corner, this piece on anthracnose in strawberry caused by the pathogen Colletotrichum , was written by myself, Steven Koike and Oleg Daugovish. It was then reviewed by our strawberry science colleagues Gerald Holmes, Kelly Ivors and Jenny Broome. Translation into Spanish (attached below) done by the Commission's Ariel Zajdband into pitch perfect Spanish in a single hour. The Commission's Joy Jacobs kept the project moving and she and Mercy Olmstead brought it over the finish line.
I'm really very proud of this team effort to put the latest settled science on a serious disease into the hands of growers, PCA's and industry people. I am privileged to work with such a great team of people!
This is interesting. In the midst of all this heat and dry I found a big run of anthracnose infected fruit, and the grower shared with me that something like 5 to 10% of his crop has the disease currently. For those who think the grower or I might be confused about this, have a look at the pictures below taken Monday early morning.
So what I did was contact Steve Koike and ask him, that seemed like a smart thing to do. He answered and said that at some point there must have been enough moisture to activate the spores. It does boil down to the "disease triangle" and each of the three requirements must be in place. We have the host (strawberries), the pathogen (Colletotrichum) and now all we need to do is have the right condition (a lot of moisture). Checking around with other growers in that area, it does seem that very close to the coast the dews over the past week were really heavy, in one case so much that one manager had to delay a spray. So the third requirement has been fulfilled after all.
Since I was able to surveil a number of fields in both Santa Cruz and Monterey counties these past few days on a soil sampling run, I found that sure enough even a little further inland the disease to is nowhere to be found. It truly does depend on the right conditions.
The savage heat of the past few weeks has really wreaked havoc on our blackberries. Normally thought of as being fairly stalwart sorts of plants, relatively easy to grow with few disease and insect issues, blackberries seem to be revealing themselves as a bit sensitive to high temperatures.
Not only are we seeing many, many cases of white druplet and subsequent necrosis (first photo), but also leaves of plants, especially at the margins (second photo), are being burned. Close readers of this space will know that white druplet is caused by intense ultraviolet radiation, and that the marginal burn of leaves probably means that the plant is not keeping up in moving sufficient water to its extremities.
Most galling however has been the large amount of red druplet disorder, better known as reversion. As one can see from the third photo below, reversion is a nuanced reddening of pretty well the whole fruit (as opposed to the starkly demarcated reddening caused by redberry mite - see elsewhere in this blog). This occurs post-harvest, meaning the fruit looks just fine at harvest and only reddens when it's been in the cooler for a bit.
It's almost certain that this fruit reddening is being caused by rapid and large changes in temperature. Research has shown that fruit with an internal temperature of over 72.5o F followed by a fairly rapid drop to cold is most likely to experience red druplet disorder. Given that in our pronounced heat spell over the past few weeks, with temperatures in production tunnels up to and even exceeding 110o F (see photo below), and movement of fruit from that environment to the mid 30's of the cooler (a drop of more than 70o F) being the embodiment of a large, rapid change in temperature, then perhaps having a huge amount of reversion shouldn't be so much of a surprise.
Ways to avoid this problem during high ambient temperatures are to avoid getting fruit that hot into the box in the first place. To whatever extent possible, early picking and quick transport to the cooler are clearly best. The other, which has been explored by researchers and may be in effect in some areas, is a staged cooling which gradually brings down the temperature to avoid the rapid shock of what forced air at 35o F imposes.