Horticulture: July 2002

In the August 1999 edition of Ag News and Views, I reported on results from our first attempt at growing strawberries using the annual plasticulture system. This system was initially used by growers on the West Coast and later refined by Dr. Barclay Poling at North Carolina State University for use by Carolina growers.

Jemstar berries at their finest

Poling's system treats strawberry plants as annuals – planted, harvested and destroyed within a 12-month period. The benefits of this system include uniform plant stands unaffected by summer disease, drought or weed competition; earlier fruit harvest; larger berry size; the potential for heavier yields; and shorter turnaround time from planting through harvest (eight months).

The variety "Allstar" was used in the 1999 study. While the total yield achieved was impressive, berry size (0.36 ounces per berry) was disappointing. Consumers have grown accustomed to the large California berries common to supermarket produce sections.

In the fall of 2001, a study conducted at the Noble Foundation Horticulture Center in Ardmore evaluated several commercial strawberry varieties using the annual plasticulture system. Another objective of that study was to determine if strawberry transplants produced in Oklahoma could compete with Arkansas-grown transplants in terms of yield and fruit quality. The study was conducted jointly with Dr. Lynn Brandenberger, research and Extension horticulturist with Oklahoma State University.

The site for the study consisted of 22 40-inch-by-30-foot permanent beds on 5-foot centers. The beds were equipped with drip irrigation and covered with black plastic mulch.

Six varieties, "Chandler," "Gaviota," "Jemstar," "Camarosa," "Sweet Charlie" and "Festival," were selected based on current industry use as a plasticulture variety or potential for use in this system. Treatments consisted of Oklahoma- and Arkansas-grown transplants of each variety with the exception of Festival, which could not be obtained from the Arkansas nursery. All 11 treatments were replicated four times and placed at random in the plot. Each treatment contained 45 plants.

On Oct. 1, 2001, transplants were set in beds on 12-inch-by-12-inch spacing with three rows per bed for a total plant population of 1,980.

Harvest began on April 22 and ended May 17. Harvest would have started earlier, but a hard freeze occurred on the morning of March 22 and destroyed many of the early-set fruit.

Results of the study are summarized in Table 1. All of the Arkansas-produced Jemstar and most of the Gaviota transplants died shortly after transplanting. Death loss of the Oklahoma-produced transplants was insignificant. Oklahoma-grown transplants out-yielded Arkansas-grown transplants regardless of variety. To be fair, the Arkansas-grown transplants were in poor condition when they were received. According to Brandenberger, the plants had been treated for a fungal infection at the nursery but still appeared to be sick when we took possession.

Click table to enlarge

Considering the condition of the Arkansas-grown transplants, the yield differences are not surprising. These results suggest that only the best quality disease-free transplants should be utilized in the plasticulture system.

Considering results from Oklahoma-grown plants only, Chandler ranked first in marketable yield while Gaviota ranked last. For many years, Chandler was the strawberry variety of choice among plasticulture growers on both the East and West coasts. Recently, Camarosa has replaced Chandler as the preferred variety based on its equivalent yield potential, superior fruit characteristics and greater resistance to anthracnose, a fungal disease common to strawberry. In our study, however, Camarosa yielded only two-thirds of Chandler's yield.

Even more surprising was the performance of Jemstar. It ranked second in marketable yield (just behind Chandler) but first in average fruit weight. Just as impressive was Jemstar's ability to produce consistently large berries throughout harvest. The berry size of Jemstar (0.64 ounces per fruit) is almost twice that of Allstar, which was used in the initial study. In a taste test conducted at the Noble Foundation, Jemstar also ranked first in both berry appearance and flavor.

The results of this study should not be considered conclusive. Growing conditions and pest populations change from year to year. Additional trials will need to be conducted over a several-year period before either the Noble Foundation or Oklahoma State University can recommend any variety with a high degree of certainty.

Despite the many questions yet to be answered, one thing is for certain – the future of annual strawberry plasticulture in Oklahoma appears to be "berry, berry" good!