Yield dynamics of primocane-fruiting blackberries under hightunnels and ambient conditions, including plant growth unit estimations and arthropod pest considerations

In 2008, primocanes of five primocane-fruiting (PF) blackberry genotypes were mown to ground level on different dates. All treatments were carried out under hightunnels and ambient conditions. Cane lengths were measured and the nodes of the same canes were counted biweekly for all genotypes and treatment combinations. Cane lengths and node numbers were regressed by cumulative plant growth units (PGU) according to a temperature response model developed by Black et al. (2007) for floricane-fruiting blackberries. Node production held a strong linear relationship to PGUs, with r2 values of 0.80 and above and similar slopes and intercepts described across genotypes and treatments. Length could also be regressed linearly, but had multiple interactions for all factors that affect growth. Although rates of node formation were linear across treatments, successive mowing treatments reduced the total number of PGU and nodes at bloom. The strong correlation of PGU to node formation and the multiple interactions of effects on length, indicate that the PGU model is valid in describing development. However, the differences in PGU and total nodes at bloom indicate growth-affecting treatments, such as mowing, can change the PGU requirements of PF blackberries.;Various methods of pruning were tested on five genotypes of PF blackberries for their potential to delay harvest. All treatments were applied to canes under hightunnels and in ambient conditions. In 2007, two tipping (removal of apical bud) treatments and one mowing (cutting cane down to ground level) treatment were applied to cultivars Prime-JimRTM and Prime-JanRTM, and selection APF-46. In 2008, one hedging (trimming hedge row at a set height, regardless of cane heights) treatment and one mowing treatment were applied to the same genotypes. In 2008, mowing treatments were applied at 3 different dates to selections APF-52 and APF-45. Yield rates (g/row-m/week) were recorded for all studies. Yield quality was assessed by recording, average berry weight, marketable yield, and soluble solids (SS) in APF-52 and APF-45.;Yield dynamics were found to be dependent on cane treatments and genotype. Mowing treatments delayed harvest, but successive mowing and mowing in June and July reduced yields. Hightunnels extended the fall harvest season in 2007, but not in 2008. Hightunnels increased average berry weight, total yield, and marketable yield, and did not affect SS content. While SS did decrease across the season, it remained within acceptable ranges for marketability.;Changing the harvest season with primocane harvests and with the temperature adjustments of hightunnels could have implications for pest management. A scale of seven phenological stages was developed to describe the development of PF blackberry floricane inflorescences. Sampling was made for three pests: blackberry gall midge (Contarinia agrimoniae), strawberry bud clipper (Anthonomus signatus), and a broad mite ( Polyphagotarsonemus latus). C. agrimoniae and A. signatus were not found on plants. P. latus, however, was found to damage blackberry leaf and flower bud development. It was also found to overwinter in Fayetteville, Ark. There were genotype differences in the population growth of P. latus, as well as significant differences between mite counts where floricanes were harvested and those where floricanes were removed during dormancy.