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.

A few things that growers and field people might being seeing this time of year in strawberry plants.

Salt Toxicity: By far the biggest issue so far in 2012 has been salt damage.  This issue is well described in the January 6 post, but a photo is included below for the sake of comparision with the other disorders.  To re-iterate, most notable characteristic of salt damage is the burnt margins of the leaves, especially on the more developed leaves.  Photo 1 below.

Fumigant Toxicity: Fumigation toxicity is another, fortunately not too common, issue that one will see at this time of year.  Every case I have been called out to has involved drip fumigation, and this makes sense, since for several reasons drip fumigants take much longer to exit the soil than shanked in materials like methyl bromide.  The process of moving out of the soil was delayed even more in the case depicted below in Photo 2 because of application into the cooler temperatures of late October, 2011.  It is notable that, in an attempt to mitigate the fumigant remaining in the beds post fumigation, this field was flushed via the drip tape with a large quantity of water and beds slit several days before planting.  Nevertheless, these activities still did not suffice, and the field languishes.

In photo 2 (taken the week of January 9) below, one can see the affected plant is struggling to establish itself and is undersized and yellow.   This is probably because its root system was compromised by remaining fumigant (doesn't need to be a lot either, it could have just been a trace) at planting and its root system is still struggling to function normally.  While this plant will undoubtedly still survive, it is unlikely to reach full yield potential.  The die was cast and its fate determined at the point of planting.

Leaf Blotch Disease:  Leaf blotch disease of strawberry normally is found all over Central Coast strawberry fields this time of year. However, since it is dependent on splashing water, it is pretty doubtful that there is much of this disease around this year. Nevertheless, since symptoms superficially mimic those of salt damage it is worth a review. 

Generally the lesions of leaf blotch disease consist of tan to gray leaf blotches that commonly, but not always, develop along the margin or edge of the leaflets. The leaf blotches are irregular in shape and are very often surrounded by a purple margin. Affected areas can grow to some size and are able to expand and cover from 1/4 to 1/2 of the leaflet surface.  To distinguish leaf blotch disease from salt damage one needs to look for the presence of tiny, brown to black, fungal fruiting bodies in the gray to tan blotches.  Photo 3 below.

As a postscript to last week’s post regarding salt and ammonium damage to area strawberry plantings, I will outline the results of the soil samples taken from a field demonstrating the symptoms described in that article.

Steve Koike and I collected soil samples from the affected field last Thursday, January 5.  Soil samples were collected from four blocks, one of which had been overhead irrigated the day previous, and consisted of composites of at least five 5” deep samples taken from around the fertilizer band by the plant roots.

Samples were immediately taken to Soil Control Lab in Watsonville for analysis.

Results are as follows:

The results are pretty clear in showing that the block (Sample 4 ) which had been watered by overhead irrigation had three times lower nitrate concentrations and about half the EC (which is electrical conductivity, a measure of salt) of the other three averaged as a group, but more equivocal on the reduction of ammonium.

To interpret the data in the table above, we can refer to work done some time ago which demonstrated EC’s in excess of 1.0 were related to loss in yield of strawberry, suggesting that real damage could occur at the 4x levels in the table above.