Mark Bolda, Laura Tourte, Rich De Moura and Karen Klonsky
of University of California Cooperative Extension have authored "Sample Costs to Produce Second Year Strawberries" which is now posted at:

http://coststudies.ucdavis.edu/files/Strawberry2ndYrCC2011.pdf

Cultivation of second year strawberries (also known as "cut backs" or "renovations" by some) is a significant part of the strawberry industry on the Central Coast, currently covering some 15% of the total acreage.   This study, which took several months of research and a raft of interviews with local strawberry growers (thank you all!), is a thorough examination of this cultural method, its costs and returns.  For growers currently growing or considering embarking on the production of second year strawberries, "Sample Costs to Produce Second Year Strawberries" is going to be a really valuable piece of literature.

It has been more than 30 years since UC published strawberry leaf nutrient diagnostic guidelines (Publication 4098, ‘Strawberry deficiency symptoms: a visual and plant analysis guide to fertilization’, released in 1980).  In the years since that publication, varieties, production practices and yield expectations have changed considerably.  In 2010 we began a project, funded by the California Strawberry Commission, to reevaluate leaf and petiole nutrient sufficiency ranges for day-neutral strawberries.  With the cooperation of many berry growers in the Watsonville-Salinas and Santa Maria areas we collected leaf and petiole samples from more than 50 ‘Albion’ fields over the past two production seasons.  In each field samples were collected 5 times over the production season, from early spring through September, to document the nutrient concentration trends from pre-fruiting to post-peak production.  Leaf samples were analyzed for total concentration of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), zinc (Zn), manganese (Mn), iron (Fe) and copper (Cu).  Petioles were analyzed for NO₃-N, PO₄-P and K concentration.

After the season cooperating growers provided yield information, which allowed us to categorize the fields as being ‘high yield’ or 'low yield’.  We then applied a process called DRIS (Diagnosis and Recommendation Integrated System) to mathematically evaluate the difference in nutrient concentrations as well as nutrient ratios between high yield and low yield fields.  This process allowed us to identify which of the high yield fields were ideally balanced nutritionally.  From this group of nutritionally balanced, high yield fields we were able to calculate a DRIS sufficiency range for each nutrient at each growth stage.

Fig. 1 shows that leaf N, P and K concentrations were highest before harvest began (stage 1, which was late February in Santa Maria and late March in Watsonville-Salinas), and declined to a reasonably stable level throughout the main harvest period (stages 3-5, May-July in Santa Maria, June-August in Watsonville-Salinas).  The decline in leaf macronutrient concentrations during the peak harvest period was expected; it happens in many fruiting crops because the leaves rapidly translocate nutrients to the developing fruit.  By contrast, micronutrient concentrations either increased from early vegetative growth to the main harvest period (as was the case for B, Ca and Fe), or remained reasonably stable over the entire season (all other micronutrients).  The vertical bars on each data point on Fig. 1 indicate the range of values typical of nutritionally balanced, high yield fields at each growth stage.  These are the DRIS sufficiency ranges; leaf nutrient concentrations within these ranges can safely be assumed to be adequate for high yield production.    

Table 1 lists the DRIS leaf nutrient sufficiency ranges for pre-harvest and main harvest growth stages.  For the sake of comparison, both the sufficiency ranges given in UC Publication 4098 and the current University of Florida guidelines have been included.  Although for most nutrients the ranges match pretty well, for others there are substantial differences.  Where the DRIS sufficiency range is substantially higher than the other sources (Ca, Mn and Fe, for example) it is because those nutrients are in such abundant supply in our coastal soils that plant uptake is far in excess of actual plant requirement; for those nutrients a lab test result marginally below the DRIS range would not be a matter of concern. 

For several nutrients (N, Zn and Cu) the DRIS sufficiency range fell below the other recommendations.  We are confident that the DRIS ranges represent nutrient sufficiency because they were determined by measuring the levels common in high yield fields.  The field survey approach used in this project ensured that a wide range of field conditions and grower practices were included, so the results are broadly representative of the coastal industry.  Also, for all three nutrients the average leaf concentrations of the high yield and low yield groups were essentially equal, suggesting that availability of these nutrients did not limit yields.

Fig. 2 shows the trends in petiole nutrient concentrations over the season.  Petiole NO₃-N was so highly variable as to be nearly worthless as a diagnostic technique; during peak fruit harvest (our sampling dates 3 and 4) petiole NO₃-N in high yield fields varied from < 200 PPM to 2,600 PPM.  While we believe that leaf total N is a more reliable measurement, this study suggests that maintaining petiole NO₃-N > 1,000 PPM pre-harvest, and > 400 PPM during peak harvest, is adequate to maintain high productivity.  Given the high variability of petiole NO₃-N it is possible that concentrations < 400 PPM would be adequate during the summer.   

Petiole PO₄-P and K were less variable than petiole NO₃-N.  Maintaining PO₄-P > 1,200 PPM throughout the season should ensure P sufficiency.  Given the high soil P availability in most coastal soils rotated with vegetable crops, this level is probably much higher than the ‘critical value’.  Maintaining petiole K > 2.5% preharvest, and > 1.5% during peak harvest, appears to be adequate.

Table 1.  Comparison of DRIS leaf nutrient sufficiency ranges with prior UC recommendations, and current University of Florida guidelines.

It's official.  As of March 8, the Federal Order will be revised to reflect that blackberries and raspberries are no longer on the regulated host list for European grapevine moth.  What this means to you as person working in caneberries is that from here on out you will not be inspected for European grapevine moth.  The link to the revised Federal Order is below:

http://www.aphis.usda.gov/plant_health/plant_pest_info/eg_moth/downloads/spro/DA-2012-07.pdf

As stated before in this space, Canada is expected to follow suit in short order.

This was a team effort and it is time to give credit where it is due.  Thank you to Lucia Varela of UCCE, Santa Cruz County Agricultural Commissioner Mary Lou Nicoletti, Sam Cooley of Driscoll's, and Leah Gayagas and John Fergusen from the USDA. 

It's a beautiful day in the Pajaro Valley.

A few notes for area growers on the current status of several invasive pests:

1. European Grapevine Moth (EGVM):  Thanks to efforts of the USDA, the Santa Cruz County Agricultural Commissioner and UCCE, the EGVM Technical Working Group has determined that evidence in the literature is scant, contradictory and does not support regulation of Rubus, and therefore recommended that this plant genus no longer be regulated for EGVM. 

Once this recommendation is written into the Federal Order (expected to happen in March, but could be later), caneberries will no longer be regulated for EGVM.  It is supposed at the level of the California Department of Food and Agriculture that Canada would also then allow caneberry fruit in again without regulation.

2. Light Brown Apple Moth (LBAM): Light brown apple moth continues to be a regulated insect in strawberries and caneberries. Therefore, inspections by the USDA of harvested fruit will continue this season, and LBAM positive larval finds at the cooler will result in field inspection and possible closure of at least part of the production field until the infestation has been eliminated.  Since a LBAM moth flight generally starts to take place in March, it is strongly recommended that growers start to now put out the pheromone based twist ties available to them from the Santa Cruz County Agricultural Commissioner.

3. Brown Marmorated Stink Bug (BMSB):  No finds of this pest yet in this area, but there have been several finds in Davis last year and one that I know of personally earlier this year.  The positive of this pest not being regulated is unfortunately heavily tempered by the difficulty of its control.   While it is by no means destiny that brown marmorated stink bug actually gets here, it is nevertheless good to be alert that the possibility has become greater over the past year.