- 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.
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
by Steven Koike
UC Cooperative Extension
Starting around mid-May and extending into June, strawberry growers and pest control advisors in coastal California are observing the fruit problem known as bronzing. This problem occurs every year to some extent but can result in large economic losses in some seasons. Bronzing results in a tan or bronzed discoloration on green and ripening strawberry fruit. Bronzed fruit have dried, rough surfaces that render the fruit unmarketable (Photos 1 and 2). The skin of such fruit can later crack.
There are three types of bronzing. Type I bronzing occurs on distinct, localized parts of the fruit, often beneath the fruit calyx or around the strawberry seeds (achenes), and is caused by insect feeding, primarily thrips (physical damage due to abrasion (Photo 3) is also very localized). Type II bronzing is caused by chemical sprays that cause a one-sided bronzing to the side of the fruit exposed to the application. In contrast, Type III bronzing covers virtually the entire surface of the fruit, occurs during certain periods of time, and can result in devastating crop loss. It is notable that Type III bronzing in coastal California tends to occur when the weather is sunny and warm.
Field-based research has demonstrated that Type III bronzing is associated with fruit exposure to stressful environmental conditions that include extreme solar radiation, high temperatures, and low relative humidity. This Type III problem is not caused by sulfur applications or feeding by thrips, mites, or other pests.
The problem is difficult to manage and prevent. Strawberry cultivars differ in their susceptibility to Type III bronzing, so growers should consider this factor when selecting cultivars for planting. Growing the strawberry crop so as to reduce physiological stress to the plants is a general overall recommendation. Observant growers and PCAs noted that commercial fields that happened to receive insecticide or fungicide sprays prior to a high temperature, high-sunlight intensity bronzing period had in many cases significantly lower bronzing losses compared to adjacent untreated fields. This situation likely occurred because commercial pesticides usually contain additives that protect the products from solar and ultraviolet radiation; such sprays also provided similar protection to the strawberry fruit.