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.

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.

There is a stream of thought currently in the Watsonville- Salinas strawberry production district of gaining advantage with earlier plant establishment this year by dramatically reducing the amount of supplemental chill, which is the cold storage of transplants following harvest, for the day neutral varieties ‘San Andreas’ and ‘Monterey’.  This might stem from reports that a number of growers in Santa Maria did well in the 2010-2011 production season with a single day of supplemental chill, and furthermore it is standard for growers in Ventura County to plant ‘San Andreas’ with a single day of chill.  For some then, it does not then seem like too much of a reach that this might be a good strategy for the Watsonville- Salinas production district.

This is worth reviewing because it flies in the face of standard recommendations for these two varieties planted in this area. There are several things going on here that perhaps contributed to the ability of some growers in Santa Maria to produce well last year with a single day of chill.  First, on average last fall, transplants were harvested 10-14 days later than normal and this spring was cooler than usual, meaning a bit lengthier cold conditioning in the nursery field and less plant stress early in the season.  Second, ‘San Andreas’ does seem to be a variety which is affected less by supplemental chill than other varieties, that is to say that it might not need quite as much.

Still, the UC recommendations do not change.  UC Davis plant breeder Doug Shaw, who brought all of these varieties into the world and therefore has an abundance of knowledge regarding them, is not changing his recommendations.   He maintains that one would want to choose transplant harvest about October 18-20 and plant early November, with two weeks supplemental chill. In all cases, plants should be chilled a bare minimum of eight to ten days. 

Never forget that supplemental chill gives the plant vigor to forgive the tough conditions of transplanting.  Planting day neutral varieties in the Watsonville Salinas district with one day of chill to gain advantage of earlier plant establishment is very much like picking up pennies in front of a steamroller.   For a possible small incremental gain, one is risking total disaster.  One day of supplemental chill is NOT recommended for University of California day neutral varieties grown on the Central Coast.