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.

A rather thorough presentation of one year’s worth of work on spotted wing drosophila was made at the big entomology meeting on September 13. As this presentation will not be posted anywhere, the following will be a summary of the work and what we know so far, along with some pointers that may be useful for growers to follow in their efforts to control this pest.

Along with various private industry efforts, the work that is being done right now by UC Davis and UCCE on spotted wing drosophila is important.  The California caneberry industry is 56% of the national fresh market production and has a production cycle on the Central Coast starting in April and continuing on until December, creating a situation of considerable potential of economic harm for this pernicious pest.

The trapping portion of this study tested two common bait formulations, yeast + sugar + water and apple cider vinegar, against a water control from late October 2010 to early September 2011.  We are still in the first year of the study so it is a bit early to draw conclusions, but over time the yeast + sugar + water perhaps performed a little better than the apple cider vinegar. Both baits tended to follow the same pattern meaning there was a period of no response to the traps (they caught very few adult flies) from late February to late May and a large increase of adult flies in the late season.  Additionally, there tended to be more females trapped than males. Whether this is a function of there simply being more females in the field than males or that the traps are simply more attractive to females remains something to be investigated.

Sampling for larvae which began mid-May of this year seems to indicate the first generation of larvae may appear before any noticeable adult fly population, and this continues later on through the season as larval peaks correlate with adult population peaks.  Larval and adult fly populations peak after the end of harvest, which only underlines that growers remove the crop as soon as possible after the cessation of fruit production.

A remaining target for us is the whereabouts of the population of spotted wing drosophila during the period of no response to traps (late February to late May).  We are not trapping flies in the fields, but obviously they start to come from somewhere when the season gets underway again in the spring.  We must understand what is going on here, as these stages of low pest activity tend to historically be the areas where the strongest measures of integrated pest management can be applied.

On occasion, we do run across ideas on how to improve our current efforts in developing a decent control regime for the spotted wing drosophila.

The use of sake ("rice wine", correctly pronounced as sa-KKE, not saki) as a trapping medium is one of those ideas.  Initially mentioned in the groundbreaking Kanazawa paper from the 1930's, it was also the subject recently of a short program on NHK (Japan Broadcasting Corporation) on managing vinegar and other flies in the household.
With the generosity of Patrick Kingston, replications of this sake trap (200 ml vinegar, 100 ml sake, 3.5 oz sugar and dubbed the "sake bomb")  were tested in the same raspberry field as the standard yeast sugar water (0.25 oz yeast, 4 tsp sugar, 300 ml water) trap.  As one can instantly see from the chart below, this trap is not as effective as the yeast sugar water trap.  Interestingly, there does seem to be a trend in the yeast sugar water trap depending how close it was placed to a potential source of a lot of spotted wing drosophila, a sensitivity not apparent in the sake trap.

Of interest, however, is the fact that the "sake bomb" was quite effective, much more than the yeast sugar water trap, in drawing in some six other species of flies, including houseflies.  This could be useful information in the case of future infestations of exotic flies.