Great collaboration yesterday with staff from UCCE, Farm Fuels, Inc., Dole, and the California Strawberry Commission to establish the research plot for Macrophomina this year. Really great group of people, it was an honor to work with you all.
A recent article referred to one of the reasons that growers need access to new strawberry varieties is that there is an inherent loss in vigor through the propagation process. That growers need access to new varieties to remain competitive is absolutely true, but that they need access to new varieties because the existing ones decline in vigor is not.
Plants do not invariably “lose their pep after years of cloning”. Indeed, reputable nurseries avoid a loss of vigor in a variety by periodically going back to meristem culture in order to keep their plant stock strong and productive. It does happen (especially in some formerly popular caneberry varieties - compare Ollalieberry in the field today to what was around in the early nineties) that older varieties of less demand don't have the meristem work done as frequently and subsequently become less vital over time.
What is meristem culture? Meristem culture is the excision of a cluster of actively dividing cells from the meristem (tip) of a newly formed strawberry runner, followed by surface sterilization, placement on a special medium, subsequent rooting, gradual acclimation of the new plant and transfer to a secure greenhouse. While some cases of genetic instability from repeatedly doing meristem culture have been noted in the literature, this cannot be described as a drift towards a loss in vigor of a variety. At any rate, programs for production of true to type (identical) plant stock using meristem culture have been used for a long time at any of the strawberry nurseries in business today.
A good example of how well and long a popular variety can be maintained through meristem culture would be the strawberry variety ‘Chandler'. Chandler continues to be widely planted by direct marketers because consumers just love its flavor and quality. Consider though that this variety was patented in 1984 by the University of California, and has had no apparent loss in vigor in all this time because the nurseries continue to go back to meristem culture to maintain it.
Growers have rumored that the variety ‘Albion' has been losing its vigor, but work at the Pomology Field Station in Watsonville over several years shows that this was not at all true. The Albion grown at this field station has experienced NO loss in yield since it was first released. Rather the rumored "loss in vigor" of the very widely planted Albion is almost certainly because of the industry wide steady drift away from methyl bromide fumigation to less effective alternatives like 1,3-D and chloropicrin.
Thank you to all of you (participants numbered in the hundreds) who completed the survey, online or at extension meetings, done over the past few months concerning what resources you refer to for production information.
Nice to see that UCCE and UC are still valued a lot by growers and agricultural professionals. We'll try and keep it that way!
Thanks to Margaret Lloyd and McNeil Roberts of UCD for putting this together and sharing the information. Really appreciate working with you both.
Interesting case documented in the pictures below of PrimeArk 45 blackberry in which the fruit did not pollinate very well. The issue is limited to one area of the field, where the grower suspects it wasn't quite moist enough during the hot spell of two weeks ago.
The problem does seem to be limited to a certain age of fruit in that area of the field, and if one recalls two weeks ago during this hot spell we didn't have much customary cooling at night.
This makes sense, since as readers know, high temperatures reduce the amount of viable pollen and consequently the success rate of germination on the pistil. It is good to know as a field diagnostician that the peripheral pistils on the flower become receptive first, and as a rule not all pistils are receptive at the same time. This goes some length to explaining the unevenness of pollination and subsequent lack of druplet formation.
I've been getting a number of calls lately concerning spotted wing drosophila in caneberries and strawberries, especially from growers on the smaller scale – in most cases organic operations.
Let's do a brief review what the best way to manage this will be:
One should take a two pronged approach. First the use of Entrust (spinosad) as a spray is recommended, while at the same time, to the extent possible, one should be removing the cull fruit (rots and over-ripes) from the field and burying them or throwing them away. For strawberry growers running the tractor over the culls in the furrow can be useful - not so much because it crushes the larvae, but because the flattened fruit dries out quickly and loses its property as a suitable food source. The spray is reducing the number of adults, while at the same time all routes of maturation are no longer available to the fly. Harvested fruit is removed and sold, and cull fruit is removed or destroyed, so there is no way for the larvae to complete their life cycle and turn into more flies.
That said, two years of research tells us to recognize that removal of cull fruit alone will not be enough to bring the population down to acceptable levels. There will always be the one fruit that is missed but yet contains the propagation potential in it to re-infest your field. That is why the best route for you is to spray along with practicing good sanitation.
Final word would be to take note of what is around your field. Are there any patches of uncontrolled spotted wing drosophila next door or wild blackberries? Both of these areas are serving as hosts and it will benefit you to get some control there also.
There is a pesticide mentioned in this article for control of spotted wing drosophila on the small scale. As always, before using such a pesticide, refer to the product label for directions on use.