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.

The UCCE Annual Central Coast Strawberry Meeting will take place this year on February 2.  The agenda is available at the website given below:

http://cesantacruz.ucdavis.edu/files/134056.pdf

Please note that the venue has changed this year from the usual Elk's Lodge.   This year's event will be held at the Kennedy Youth Center, 2401 E. Lake Avenue in Watsonville. 

Happy New Year everybody.

Unfortunately, we start out the year with some concerns. We want to alert growers that early in 2012 we are seeing transplant decline and dieback in various fields in the Watsonville-Salinas production district. As pictured below (Photo 1), this problem can be quite severe and characteristically affects a large percentage of the field. From what we have seen and heard from others, along with samples submitted to the UCCE disease diagnostics lab in Salinas, this decline is widespread and seems to be particularly acute in organic fields.

On closer inspection (Photos 2 and 3 below), the symptoms closely resemble those caused by high salt levels. Margins of the oldest leaves show the initial symptoms and become brown, dry, and burned. As the condition worsens, the entire leaf will wither and die. Eventually all leaves can turn brown and the transplant can actually die (Photo 4 below). Generally the internal crown tissue is sound and intact; however, as the plants continue to decline, some of these crowns turn brown and become discolored.

These transplant decline and death symptoms superficially resemble symptoms caused by Colletotrichum (anthracnose) and Phytophthora (crown and root rot). However, lab tests thus far have failed to recover any pathogen associated with these plants. In addition, the widespread (up to 75%, in some cases) incidence of declining transplants argues against a biotic agent as the cause of this problem. The problem appears to affect all cultivars and is not restricted to any one source of transplants.

What is causing all of this damage? For fields we have investigated, the water EC (electrical conductivity, a measure of salinity) is normal and the soil is not excessively saline and has never exhibited these symptoms before. Again, dieback symptoms are occurring across varieties, across nurseries, and across blocks. There is some indication that damage is more severe in wetter areas.

The exceptionally dry weather of the past five to six weeks may be playing a significant role in this development. The total lack of rain has forced strawberry growers to irrigate often, and in many cases this has been solely through the drip tape. While this amount of water is sufficient for plant needs, we should take into account that the beds are therefore not being leached by the abundant amounts of water that an inch or two of rain can bring all the while that the bands of pre-plant fertilizer amendments are accumulating salts around them and mineralizing into what can be predominantly ammonium forms of nitrogen in cooler soils. High levels of ammonium are associated with toxicity in plants, as are the accumulated salts.

So this leads us to believe that the leaf burn and transplant dieback being seen up and down our district is being caused by an accumulation of ammonium and salts around the roots because of a lack of leaching.

Interestingly, the most severe leaf burn problems have been in organic strawberry fields supplemented with pre-plant fertilizer. This pattern is consistent with what we know about these fertilizers, which are amendments such as blood or feather meal, meaning that they are fully mineralized in a matter of weeks after incorporation. Therefore, fields containing these fertilizers likely right now have significant amounts of ammonium accumulated in addition to the salts concentrated around the roots due to the lack of winter/spring leaching. 

If our hypothesis is correct, growers who have this problem should counteract the buildup of harmful agents by irrigating with overhead sprinklers or at the very least with heavy watering through the drip tape. Overhead irrigation is a good substitute for rain and provides the abundant amounts of free water needed to move the ammonium and salts away from the plant roots where they are causing harm.

In a conversation with a Pest Control Advisor colleague the other day, we discussed the merits of lime sulfur applications in the fall on blackberries grown in the Pajaro Valley.  This is something I have spent considerable time thinking about and have come around to believe, that while not completely supported by empirical evidence, fall application of lime sulfur might not be necessary in our blackberries and is to some extent an artifact of past varieties and practices. 

Here is why I maintain fall applications of lime sulfur might not be necessary in blackberries:

1- Redberry mite is not controlled by fall lime sulfur.  It is rather controlled by post - bloom applications of horticultural oil or sulfur.  This is a fact and has been tested.

2- Lime sulfur used to be critical to control cane and stem rust, Keuhneola uredinis, on the trailing Ollalieberry and continues to be very effective when applied for this disease on that variety in the fall.  However, none of our current Arkansas varieties (Apache, Navajo, Choctaw and so on), nor are the proprietary suite of varieties known to be susceptible to this rust.   I have yet to see it on the primocane bearing PrimeArk either.  I did see a touch of orange rust on a proprietary variety last year, but this rust is not controlled by lime sulfur.

3- Do a mental exercise to test the thesis that fall lime sulfur "cleans up" the remaining blackberry cane in the fall.  Mites? Not a great material for these, ditto on whitefly and aphids if they are even around.  Quite effective of course on powdery mildew (NOT downy mildew), but again this pathogen is better addressed in my mind a little later in the season when the leaves emerge and fungus more active.

I would enjoy very much for someone to prove me wrong and leave replicated strips untreated with lime sulfur and see what happens next year.  I believe this would be useful demonstration and quite possibly a beneficial exercise for the industry as a whole.

The use of lime sulfur is discussed extensively in this article.  Before using lime sulfur or any of other pesticide, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.