Static-V trellis increases raspberry yield, but fruiting shoots grow toward its center making harvest difficult. Shading causes early leaf abscission and it favors fungus diseases inside the V. Static training of floricanes and primocanes to opposite sides of a V trellis prevents neither harvest difficulty, nor primocane injury during harvest. In 1988-89 harvest difficulties were reduced by bloom-time shifting of floricanes on a V-trellis. Over 90% of fruiting shoots were oriented to the trellis ' exterior, but primocane shading and early leaf abscission continued. The 'bent fence' trellis was designed and tested in 1989. It shifts floricanes from horizontal orientation to an upright position on one side of a V-shaped trellis, thus retaining outward display of fruiting shoots and achieving unobstructed display of primocanes on the opposite side. Harvest efficiency, disease reduction, accurate deposition of pesticides, avoidance of solar injury (sun scald), and adaptation of mechanical pest control procedures are potentiated by this system. It also reduces impediments to studies of carbohydrate partitioning, photosynthetic efficiency, yield efficiency, and intraplant competition.
Herbert D. Stiles
Three different “shift-trellises” were designed to localize the fruiting zone and to separate it-from vegetative structures. This allows efficient manual harvests by making berries more visible and easier to reach. It improves the quality of manual harvest conditions by reducing human contact with thorns (i.e., prickles).
Better definition of the fruiting zone's dimensions and location, important factors in mechanical harvesting, is possible with these systems. One system allows horizontal placement of the fruiting zone as in the Lincoln Canopy System, but with an inverted orientation of the fruiting shoots. Inverted orientation of fruiting shoots will shorten the distance to the mechanical harvester's collector surface. This changed juxtaposition among trellis components, floricanes and fruiting shoots will eliminate most obstacles against which berries might impinge during their fall to the collector surface. A new kind of agitator may be required to effect fruit removal in this system.
Herbert D. Stiles
The Stiles bent fence (SBF) and single-sided shift trellis (SSST) are differently designed structures that function to isolate fruiting zones of summer-fruiting brambles on one side of the plant or row. The SBF and SSST are suited for use with cultivars that produce long, flexible, nonbranched canes. Summer pruning of stiff-caned, semi-erect types may encourage development of long, flexible lateral branches that are adaptable for training on these trellises; alternate-year cropping may be helpful where such pruning is necessary. The SSST operates on the same principles as our original single-sided trellis (SST), but the newer design is compatible with a broader range of commonly available construction materials. Construction plans will be published in a Virginia Agricultural Experiment Station Bulletin as soon as funds are made available. The SSST should allow greater manual harvest efficiency, more effective IPM, fewer yield losses to sunscald, compatibility with cultural management practices, lower costs of postharvest precooling, better condition of harvested fruit for maximum shelf life, and stronger prospects for machine harvesting of fresh-market brambles.
Herbert D. Stiles and Paul J. Semtner
Blackberry drupelet development is influenced by a number of agents (Ellis et al., 1991; Moore and Skirvin, 1990). We have observed poor drupelet-setting and `nubbins' that were not attributable to common pests, such as tarnished plant bug or diseases. In seeking causes for such problems during 1986, we discovered tiny (diptera) larvae in unopened flower buds and newly opened blossoms of wild-growing and domestic blackberries. Pistils and stamens of infested buds and blossoms showed signs of necrosis; injuries seemed worse in buds that contained more larvae. We confirmed relationships among bloom-time symptoms, drupelet setting, and fruit weight by tagging symptomatic and asymptomatic postanthesis blossoms on 22 May 1989. One week before the normal harvest season, symptomatic berries averaged 38 mg and asymptomatic berries averaged 208 mg. Twelve symptomatic blossoms (27%) produced no drupelets, 19 (43%) produced one to 10 drupelets, and no symptomatic blossom yielded a normal berry. We devised or adapted larval collection and rearing apparatuses and procedures to obtain adult midges that were needed for taxonomic speciation of this new blackberry pest. During 1994, SEL identified resultant specimens as Contarinia agrimoniae Felt. This genus previously had not been recorded from Rubus buds, and little is known of C. agrimoniae habits, life cycle, etc. Additional studies are needed to identify procedures for management of C. agrimoniae.
Herbert D. Stiles and Paul J. Semtner
Larvae of Contarinia agrimoniae Felt, a gall midge, were discovered during 1986 in blossoms of blackberry cultivars and wild-growing plants that had a history of poor fruit set and `nubbin' formation (Stiles, Semtner, and Reed, 1996). Other species damage blackberries in Europe, but the only North American recognition of Rubus flower bud infestation was with Dasineura rubiflorae Felt during 1886 (Gagne, 1989). During 1995 we found larvae of a Dasineura spp. in damaged buds at two, widely separated, commercial, North Carolina, blackberry sites. It is not known if the latter insects are different from the species that was collected during 1886. Midge larvae probably overwinter in soil under affected plants so we sprayed diazinon on the soil surface before bloom to kill larvae or interfere with pupation and reduce crop injuries. Infested `Shawnee' and `Cheyenne' buds were ≈100% more numerous among controls than diazinon-treated plots. Numbers of larvae varied among infested buds; 83 were observed in one bud from a nontreated `Cheyenne' plot.