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.

The hot weather of this past week has unsurprisingly caused a certain amount of sunscald on caneberry fruit.   As can be seen in the photos below, sunscald manifests itself as a white to brown discoloration of one or more of druplets on mature and immature fruit.

The current round of sunscald has accompanied the hot spell of the past three days, and this is consistent with what we have witnessed in the past.  Any time on the Central Coast that we go from fairly steady temperatures in of 70^oF to suddenly around 90^oF with an absence of fog, we experience significant increases in sunscald.

While it may seem that the sunscald of raspberry fruit is caused by simply very hot weather, it is a little more complicated than that and it is actually radiation from the sun which is causing the problem.  Apparently, this radiation causes enough physiological changes within the fruit to discolor it, but not causing it to become necrotic right away.  Humid air, which in our area tends to be cool (think fog), scatters and absorbs radiation from the sun, while hot air tends not to carry too much of the radiation scattering moisture and therefore is not doing as much to scatter it and prevent it from damaging fruit druplets.  Windy weather is even worse, since it is moving the moisture out and away from the canopy.

There are several solutions to this problem.  One, the least practical, is to introduce moisture into the canopy via overhead irrigation.  It is best of course to do this in the early morning, to ensure that the flowers and fruit are dry by the evening.  Another is to use some form of shadecloth to cover the plants, which many Pajaro Valley growers are already doing to a certain extent in the form of macro-tunnels, where very little sunscald has been observed.   Finally, it is known that some varieties are more susceptible to sunscald than others, so if one is consistently having problems with sunscald, switching varieties might be a good solution.

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.