- Author: Mark Bolda
by Tim Hartz and Mark Bolda
During the 2010 production season we conducted a survey of approximately 30 commercial fields in the Watsonville-Salinas area to develop information on strawberry nutrient requirements, and to evaluate current fertilizer practices. We did whole plant sampling in four fields, two planted with ‘Albion’ and two planted with a day-neutral proprietary variety. In all fields the uptake of nitrogen was slow through the winter months; by the end of March total crop N uptake was less than 20 lb/acre. From that point forward, crop N uptake was quite steady, averaging between about 1-1.2 lb N per acre per day. By the end of August, total N uptake ranged between 140-190 lb N/acre, with the higher amounts in higher yield fields. Total phosphorus (P) and potassium (K) uptake averaged about 40 and 230 lb/acre, respectively.
Soil sampling showed that the majority of fields began the season with high soil test levels of P and K, in many cases high enough that P and K fertilization would not be required to produce a good berry crop. However, it appeared that growers often follow a preplant ‘recipe’ when it comes to fertilization, and that typical ‘strawberry mix’ controlled release N/P/K fertilizers were nearly always applied, regardless of soil test nutrient levels. The efficiency of nitrogen applied preplant is also questionable. The N in common preplant controlled release fertilizers becomes available at a relatively steady rate over 6-8 months, meaning that if applied in late October more than half the N is likely to be released by the end of March. Since crop N uptake by the end of March is less than 20 lb/acre, any additional fertilizer N released by that time will be subject to leaching by rain or irrigation. A moderate amount of preplant controlled release N provides a guarantee of some N availability during the winter, but a large fall application is likely to be inefficient.
Most of the growers we worked with provided us with their fertilization records. On average, they applied a seasonal total of 187 lb N/acre, about evenly split between preplant and fertigated N. However, there were large differences among growers in their N management; seasonal rates varied from less than 150 lb N/acre to nearly 300 lb N/acre, with some growers using nearly all preplant N, while others applied nearly all N through fertigation. We found no correlation between seasonal N rate and fruit yield.
- Author: Mark Bolda
by Steven Koike, UCCE
Leaf blotch disease of strawberry is being detected in some fields in coastal California this winter. Dependent on splashing water, this disease rarely occurs unless overhead sprinklers are used or rains occur. Symptoms generally consist of tan to gray leaf lesions that commonly (though not exclusively) develop along the margin or edge of the leaflets. Leaf blotches are irregular in shape and may be surrounded by a purple border. These affected areas tend to grow fairly large; they can expand and cover from 1/4 to 1/2 of the leaflet surface.
A key diagnostic feature of leaf blotch is the presence of tiny, brown to black, fungal fruiting bodies in the gray blotches. Brown to black petiole lesions can also occur. In past seasons leaf blotch has been misdiagnosed as spray burn or phytotoxicity from applied chemicals. If uncertain about the nature of such leaf symptoms, submit samples to the UC Cooperative Extension offices in the coastal counties.
Leaf blotch disease is caused by the fungus Gnomonia comari, which also has the name Zythia fragariae. Zythia fragariae survives on strawberry crop residues. The fungus does not appear to be a true soilborne fungus, so it will not likely persist in soil unless strawberry crop debris is present. The Zythia form is especially dependent on splashing water for spore dispersal and infection. This accounts for the typical appearance of leaf blotch during winter and early spring seasons when there are rains. Leaf blotch is usually considered a minor problem and fungicide treatment programs have not been developed nor are they generally recommended. The strawberry plants usually grow out of the problem. Leaf blotch spread and development is dependent on rains and splashing water, so once the winter rains cease, leaf blotch usually becomes a non-issue for growers.
- Author: Mark Bolda
One of the first posts to this blog regarded the importance of chill, both field and supplemental, to the day neutral (ie Albion, San Andreas, Portola, Monterey among others) strawberry varieties. Right now, field chill in MacDoel is in the area of 600 hours, which is plenty, even in the light of the very warm stretch of weather that took place in September. Still, be reminded that this abundance of field chill should not be considered to be a replacement for supplemental chill taking place in the cooler after the transplant has been harvested.
However, this year because of the delay in transplant harvest growers really should be striving to strike a balance between getting adequate supplemental chill to obtain good vigor and planting sufficiently early to get sufficient plant growth here in the fall. To accommodate this idea, every one of the day neutral varieties listed above can be well established with supplemental chill of 7 to 10 days, but no less. More days of chill, up to 18 days, are of course in the printed recommendations, but this year a large delay in planting may not result in acceptable plant growth and establishment.
If one follows the suggestion given above, supplemental chill will end up being on the low side, and subsequently growers must be more vigilant than usual in planting practices. Transplants must not be allowed to dry out in the field during planting, transplants should be properly placed the planting hole (no “J” rooting, and only portion of the crown above the soil line) and irrigation for establishment should keep the beds at field capacity for a few weeks.
- Author: Mark Bolda
Introduction: As the planting season for strawberry approaches, it is useful to review some concepts of strawberry plants and planting. Strawberry growers occasionally have questions about the size of strawberry transplants (i.e. crown size) and its effect on plant growth and yield.
The following is a summary of a study run over two years as an investigation of whether strawberry crown size had any effect on strawberry fruit yield and size.
For those who want to see the full report, it starts on page 5 of the Monterey Crop Notes for November/ December 2007.
http://ucanr.org/cropnotestransplant2007
Materials and Methods:
Treatments: The trials were conducted in a well managed organic farm in Moss Landing, CA. In year one, the study consisted of treatments of “large” and “small” size transplants. Measurements were done with a caliper at the middle of the crown. The following varieties were tested at the sizes given below:
Seascape: small < 1.1 cm, large > 1.2 cm
Transplants were dug 10/27/04 in Macdoel, and planted 11/16/04.
Aromas: small < 1.1 cm, large > 1.3 cm
Transplants were dug 10/26/04 in Macdoel, and planted 11/9/04.
In year two, the study included a third treatment, consisting of “slicks” (known as “lisas” in Spanish) for the varieties of Seascape and Albion. “Slicks” are very small crowns which are almost entirely made up of primary roots and no secondary roots, giving them a smooth appearance (see photo accompanying this article).
Seascape: “slicks”, < 1.1 cm, large > 1.2 cm
Albion: “slicks”, small < 0.9 cm, large > 1.1 cm
Both Seascape and Albion transplants were harvested in MacDoel 10/25/05, and planted 11/22/05
It should be noted that the large crowns in each treatment were not a common feature. In each box of 1000 crowns large crowns represented probably 5-10% of the total numbers of plants.
Plants were measured for plant diameter early in the season, possibly on a monthly basis. Fruit yield, both count and weight of fruit from each replicate plot, were evaluated by harvest by qualified personnel harvesting on a regular schedule.
Results: In the first year trial, plants of treatments planted to small crown sizes had smaller diameters than larger crowns one and a half months after transplant. Three months after transplant this difference had disappeared. There were no significant differences in plant diameters at any date in any size categories for the varieties tested in year 2.
Fruit production was significantly lower in smaller crowns of Aromas in the summer months of year 1, and resulted in lower total fruit production. There were no differences in fruit production in year 1 or year 2 for Seascape.
For Albion, fruit production for "slicks" and small crowns was significantly lower than large crowns in the months of June and July, but there were no differences in total yield between any size class.
With very little exception did fruit size vary significantly between any of the crown size treatments by month or through the season.
Discussion: Although there was some variation by month for certain varieties, transplant crown size was not a good predictor of total strawberry fruit productivity in this study. What this means is that, while there was some cyclicality in production for some varieties, size of the strawberry transplant did not have an effect on total fruit yield.
- Author: Mark Bolda
Mark Bolda
Hillary Thomas
The use of pheromone based twist ties has found significant success in reducing the incidence of light brown apple moth mating in caneberries grown on the Central Coast of California. With the recent advent of light brown apple moth infestation in area strawberries, especially those in organic production, there has been a groundswell of interest on testing the same technology there.
The following is a brief description of a trial mounted on the part of the authors in testing whether the use of pheromone based twist ties could be useful and successfully applied in strawberries. On June 15, twist ties wound around chopsticks were distributed evenly (every other strawberry row with 16 to 18 feet between each stick) across 8 acres of organic strawberry at the rate of 300 per acre (higher end recommended label rate), with another 8 acres left alone as an untreated check. This was replicated 4 times in various fields around Watsonville.
A matrix of twelve traps using pheromone lures was placed in each 8-acre field to test the ability of the pheromone based twist ties to prevent males from finding females emitting the same pheromone. The idea is that if the males are unable to locate the pheromone lure in the trap, they will not be able to locate females and subsequently not be able to mate, resulting in population reduction.
Traps were checked yesterday, June 29. Out of the 48 total traps placed over the four treated plots, only a single male moth was captured, while the traps in the untreated check contained two moth males on average.
Trap Captures of Light Brown Apple Moth Males, June 29, 2010
Totals are from 12 traps in each plot
with pheromone without pheromone
Field 1 1 23
Field 2 0 27
Field 3 0 23
Field 4 0 42
The results suggest the twist ties may be useful as part of an integrated strategy to reduce light brown apple moth populations in fields, especially for organic growers who have limited available management tools.
