This post is to announce a meeting on strawberry mineral nutrition to take place this coming January 30.  I think it might be good to spend a little bit of time on the current salt situation as well, seeing as it is related to nutrition and water.

First presentation will be in Spanish, and the second in English, with translation provided for both.

Growers and PCA's - bring a copy soil and/or tissue sample analysis for review of sufficiencies/deficiencies/toxicities in our final exercise.

Look forward to seeing you there!

I was brought out to the situation in strawberry pictured below.  Yellowing leaves and very little flowering or fruiting.   For whatever reason, the street’s call on this was that it is iron, but to me the youngest leaves being as green as they are (Photo 2 below), is a dead giveaway that it’s not iron, because the youngest leaves in iron deficient plants are the first to yellow, not the last.

No sense standing around arguing about the problem, we just have to roll up our sleeves, get dirty and figure it out! 

The charts below are threefold replicates of sampled leaves and soil of affected plants in the field.

Table 1 : Tissue analysis

Table 2: Soil analysis

So, it looks like the main culprit here is indeed a lack of nitrogen, seeing that at an average of 1.4% it is well under the 2.4% tissue concentration threshold given in the UCCE nutrient guidelines.  Just to be sure though, we should check to see if any of the other nutrients are low, but they are not and everything else is within normal ranges.  I would have some concern about the high levels of sodium (197 ppm) and chloride (7930 ppm), but beyond some marginal burning of the leaves, these plants don’t seem to be exhibiting symptoms consistent with real salt poisoning.

Looking to the soil, sure enough we get confirmation of what we are seeing at the tissue level, and see that nitrates are pretty low here, running at a lean 4 ppm.  I would probably want to bump that up a bit.

So what does cheap natural gas do for California berry growers?  Not a lot apparently, if one extrapolates from an excellent article written by Colin Carter and Kevin Novan and recently released by the Giannini Foundation of Agricultural Economics titled “Shale Gas Boom: Implications for California Agriculture.”

http://giannini.ucop.edu/media/are-update/files/articles/V16N3_1_1.pdf

As most Americans know by now, the ability to access through hydraulic fracturing (known in the common parlance as “fracking”) previously unavailable shale gas resources portends an big shift in the energy dynamics of the United States.

The enormous amounts of shale gas becoming available through fracking in the US has brought about a drop in the price of natural gas nationwide, but this has not been followed with a worldwide drop in natural gas prices.   Natural gas, moved as a gas through pipelines domestically, can only be transported to overseas markets once it has been converted to liquefied natural gas (LNG) at facilities where the gas is turned into liquid form and then pumped into tankers for transit. The current lack of such facilities in the US and subsequent difficulty to get our natural gas to foreign markets has resulted in huge price discrepancies globally, with natural gas prices in the US at approximately $3.30 per thousand cubic feet, at the same time in Europe for example prices are $12 per thousand cubic feet.

This price discrepancy of course presents a real cost advantage for users of energy and natural gas in the US over their overseas competitors.  How much of this price advantage accrues to California berry growers is a question worth examination.

According to the article cited above, only 0.8% of total natural gas consumption in the US occurs in the agricultural sector.  A lot of farm equipment, from tractors to motorized implements to trucks, use gasoline or diesel rather than natural gas.  Obviously, if a lot of this equipment were to be converted to use natural gas there would be some cost advantage, but this is very much a proposition for the long term.

On the other hand, natural gas is the main input in the production of ammonia, which is subsequently converted to the nitrogen fertilizers which are a mainstay of California berry growers, who use anywhere between 160 to 250 lbs of the stuff per acre.  However, fertilizer costs in the berry industry, according the UCCE Cost and Return studies make up only 1% percent of the total cost of production, meaning that price changes in nitrogen fertilizer are not that meaningful in one direction or another to the total cost of running a berry operation.  Furthermore, fertilizer prices are arbitraged internationally, meaning prices tend not to vary too much from country to country, so low fertilizer costs stemming from cheap natural gas feedstock in the USA don’t really translate to much of a cost advantage to local growers anyway.

The other possibility where cheap natural gas prices could confer an advantage to California berry growers would be a reduction in the price of electricity, more than half of which in California is generated from natural gas.  The heavy reliance on irrigation and the use of electricity to get that water out of the ground in California agriculture and the berry business at least superficially points to some savings from reduced energy costs.  However, digging into our latest Cost and Return studies, pumping irrigation water constitutes only about 1.5% percent of the total cost of production of berries.   The gains from cheaper gas and subsequently cheaper electricity will be not that significant in other words.

In conclusion, the increasing amounts of shale gas becoming available through fracking in the US, while offering some possibility of advantage over the long haul in terms of energy inputs for traction and transport, does not appear to give a lot of advantage currently to California berry growers over their foreign competitors in terms of cost of production.

Since June of this year there has been a spate of yellowing and senescing (dying) of leaves of certain raspberries.  This problem is widespread in the Watsonville and Salinas production district and first appears as a yellowing of the older leaves toward the bottom of the plant.  The symptoms appear evenly distributed through the field with very little patchiness in incidence.  The yellowing tends to follow a mottled pattern (Photo 2 below) and surprisingly can be pretty bounded on the leaf, for example on one half and not the other.  Affected leaves end up separating from the main plant quite easily.  The yellowing and dieback most often occurs on the lower half of the plant, and rarely advances higher nor does it result in total plant death.  From growers and personal observations this yellowing and senescing usually does not appear to result in any reduction in plant vigor or yield, but there are occasions of total plant loss.  There are reports of occasional loss of fruit integrity and crumbliness in affected fields, but this is strictly anecdotal.

The lengthy report below is a summary of the multifold approach we took to studying this issue followed by a discussion at the end regarding what is the most likely cause.

Arthropods:  Arthropods are not the cause of this problem.  One grower reported a correlation with a certain type of mite and while there were patches of twospotted spider mites in some locations, in others there were none nor had there ever been.  Beyond the mites, no other arthropods capable of causing leaf discoloration or necrosis were found.

Diseases:   The leaf yellowing is not caused by a pathogen.  A total of five whole plant samples (plant tops and roots) from several fields experiencing leaf yellowing were submitted to the UCCE diagnostic laboratory in Salinas, and in only one case did the test come up positive for a species of Phytophthora.  As leaf yellowing can be caused by virus infection, for example Raspberry Bushy Dwarf Virus on the Autumn series of red raspberry, a set of leaf samples was tested at the UCCE diagnostic lab in Salinas and another distinct set totaling five samples was submitted to the CDFA disease diagnostic laboratory in Sacramento.  All tests for virus came back completely negative.

Nutritional:  Levels of nitrogen and phosphorous are below sufficiency and substantially lower in yellow leaves than in green leaves, and levels of calcium are above sufficiency (and well above sufficiency in a field of healthy green plants) and higher in yellow leaves than in green leaves.  Soil concentrations of nitrates are below recommended levels of at least 10 ppm in three of four fields experiencing yellow leaves.  Concentrations of the salts sodium and chloride are substantially lower in all fields experiencing leaf yellowing than a field of symptomless, apparently healthy plants.

Table 1.  Leaf Samples. ‘Healthy Green’ refers to leaf samples taken from a field experiencing no yellowing anywhere; other Green and Yellow are paired sets coming from the same field and leaves collected from floricane at the same approximate height of about 18" above the soil.  Samples consisted of at least 15 leaves coming from various parts of the field taken between July 16 and July 27.

^*Healthy sample excluded from these calculations.

Table 2. Soil Samples. Soil samples are a total of 10 6” deep cores taken from areas experiencing yellow leaves.  The surface crust of the soil was brushed away before sampling.   All soil samples were taken July 27.

^*The designations “Healthy Green, Yellow 1, Yellow 2 and so on correspond with the same designations for the leaves above, meaning they come from the same fields.

Discussion:  This issue of yellowing leaves in raspberry is not being caused by insects, mites or disease but we do find a striking difference in the concentration of some nutrients in affected leaves and the soils from from which they come.  Since all the fields in question here are being managed by extremely competent and experienced growers we can be certain this nutritional deficiency is not being caused by a simple lack of fertilizer application, so we must explore this a little further.

All of the plants experiencing leaf yellowing and senescence are being grown in macro-tunnels.  The PCA attending each of these fields reports that they have been very warm on the inside compared to outside and interestingly found a high level of humidity as well.   This adds something to our investigation, since high temperatures can be a factor affecting the growth of plants, especially plants such as raspberry adapted to temperate climates. Heat injury in plants often results leaf yellowing and senescence.

Leaf nitrogen and phosphorous are lower in yellow leaves than green leaves.  Leaf senescence is often preceded by the degradation and subsequent loss of chlorophyll, the lack of which of course means the leaf stops being green.  A quick perusal of a book concerned with the mineral nutrition of plants (the excellent “Mineral Nutrition of Plants” by Horst Marschner I recommend highly) tells us that leaf senescence results in a net mobilization or export of nutrients from the dying tissue to still living and growing tissue.   And we are seeing exactly this in the fields, since the plant tops continue to flourish and produce flowers and fruit all the while the bottoms are yellowing and dying.

But what of the higher concentrations of calcium in yellow leaves compared to green?  They are quite high, near or above what are normally considered levels of sufficiency.  Calcium, in contrast with other plant essential minerals is moved from the roots to the rest of the plant via evapotranspiration through the water conducting elements (also known as the xylem).  This is meaningful since this means we tend to see higher levels of calcium deposition in plants moving lots of water.

Soil concentrations of nitrate, sodium and chloride are all low in fields experiencing leaf yellowing and necrosis.  Knowing however that all three are leachable by water is again helpful.

The Bottom Line: What we are getting is that the tunnels are hot and killing some of the leaves towards the bottom of the plant.  The plants continue to grow though, reallocating nutrients from the dying leaves to the younger ones and pulling up plenty of water because the rate of evapotranspiration is high in the heat of the tunnel.  The grower response of adding more water to keep up is of course the correct one, but this is resulting in a lot of leaching.  For salts like sodium and chloride this good, for a plant essential ion like nitrate it is not.  So not only is nitrogen being transported away from the dying leaves, it is also being leached away in the soil before the plant can get it.

Probably the best response to this situation would be the one which has already been taken, and that is to open the tunnels to enhance air circulation and lower the internal temperatures. 

I would like to thank PCA Eryn Gray for sharing his data and insight along with the growers involved in this work without whose participation none of this would have possible.