The Vegetable Growers News

Both Heritage (foreground) and Autumn Britten red raspberries performed well in high tunnels.

Penn State Researchers Grow Quality Fruit in High Tunnels

By Kathy Demchak and Bill Lamont Penn State University

Over the past two years, research has been conducted in high tunnels at the Center for Plasticulture’s High Tunnel Research and Education Facility at Penn State University. Crops grown have included an assortment of various vegetables and cut flowers, and, in four of the tunnels, strawberries, primocane-bearing red raspberries, and thornless blackberries. Originally it was expected that this growing system’s main advantage would be season extension, with resultant yield increases. Yields did increase, but in addition, fruit quality was improved, and pesticide use was markedly decreased. A trial was initiated where strawberry plants were grown in a system very similar to plasticulture in the field, except that the plants were in a high tunnel. The cultivars Sweet Charlie, Camarosa, and Chandler were planted on Aug. 18 and Sept. 22, 2000 in a plasticulture system using 1.5 foot-wide raised beds with black plastic mulch and trickle irrigation. Chandler was the highest yielder, with plants producing about 1.25 pounds of fruit per plant, compared to 0.9 pounds of fruit per plant in field production at the same site. Berries were ripe three weeks earlier than the same cultivars grown as plasticulture berries in the field. Two problems, however, included a high occurrence of powdery mildew and a rather impressive population of two-spotted spider mites. This year, the fungal hyperparasite AQ-10 (a fungus that feeds on powdery mildew) is being tried, but it’s too early to tell whether this results in an acceptable level of control. Predatory mites eventually brought the mites under control, but should have been released sooner. In colder areas of Pennsylvania, early frosts have resulted in only a small portion of the crops of most primocane-bearing raspberry cultivars being harvested. For example, only 15% of the potential yield from Heritage was harvested during research trials conducted at this site during 1994-1997. In addition, low winter temperatures resulted in no crop on thornless blackberries year after year even though the foliage grew beautifully. High-tunnel production was expected to extend the period during which raspberries could be harvested, and mitigate low winter temperatures, making thornless blackberry production possible. Autumn Britten and Heritage plants were planted in 2000 and harvested in 2000 and 2001. Plant spacing was wide, at eight feet between rows, with an original plant spacing within the row of 18 inches. Autumn Britten yielded nearly one pound of fruit per linear foot of row in 2000, the year of planting. Heritage, however didn’t begin yielding significantly until the beginning of October. It was just reaching peak production in late October when the temperature unexpectedly reached 22°F in the tunnel, bringing harvest to a halt. For the second fruiting year, Autumn Britten was pruned to the ground in the spring because it had had very little bearing cane length remaining. Heritage, however, was cropped as both a summer bearer and fall-bearer. Yields in 2001 from the planting were extremely high. Autumn Britten, cropped as a fall-bearer only, yielded 2.5 pounds of marketable fruit per linear foot of row. Heritage yielded over .75 pound of fruit per foot of row as a summer-bearer, and an additional 3.5 pounds per linear foot of row as a fall-bearer. Vegetative growth of blackberries was impressive, with new canes from these plants reaching the roof of the tunnel by early July. Triple Crown, also planted in 2000, yielded 3.6 pounds of marketable fruit per foot of row during 2001, its first fruiting year. While yield was high with the right management, the most promising aspect of production for brambles was extremely high fruit quality, with 98% of the raspberry fruit marketable in 2000. In addition, fruit held under refrigeration had not grown any mold even after 11 days of storage. In 2001, percentage of marketable yield was lower, at 93-95% of the fruit for all brambles, mainly because some berries were missed during harvest due to dense foliage. No fungicides were used on any of the brambles during either year. The problem of Japanese beetles during 2001 was eventually brought to manageable levels through a combination of hand-picking and traps placed outside the tunnels. In a second bramble experiment, two new cultivars of primocane-bearing raspberries (ND-F1, and the recently-named Josephine) and a Wyeberry (a raspberry/blackberry hybrid) selection (QDE-1) are being grown compared to Heritage as a standard. These new cultivars are from the cooperative small fruit breeding program in New Jersey, Maryland, Virginia and Wisconsin. Initial trials by the breeding program cooperators, had excellent size and flavor. Plant spacing is much closer in this experiment to maximize yield per area, at four feet between rows and one feet between plants. However, plants were planted six weeks later in 2001 (late May of 2001 rather than mid-April of 2000) due to a lack of availability of the selections, and it became apparent that an early planting date is critical to the success of this system in the first year. Yields from this planting were negligible for the first year, unlike in the previous planting. This might be less critical in warmer areas, where a longer fall harvest season could counter the effect of a delay in planting. In any event, plants should be planted as early as possible in the spring. While it is obvious that many of the ‘bugs’ still need to be worked out in future research, it is expected that high tunnel production of small fruit is likely to have a solid place in grower operations. High tunnel production should be of particular value where a premium market exists for high quality fruit produced with little or no pesticide use. However, until experience is gained, this growing system should be tried on a limited basis.