Eric T. Stafne

Blueberry Producers’ Attitudes toward Harvest Mechanization for Fresh Market

The availability and cost of agricultural labor is constraining the specialty crop industry throughout the United States. Most soft fruits destined for the fresh market are fragile and are usually hand harvested to maintain optimal quality and postharvest longevity. However, because of labor shortages, machine harvest options are being explored out of necessity. A survey on machine harvest of blueberries (Vaccinium sp.) for fresh market was conducted in 2015 and 2016 in seven U.S. states and one Canadian province. Survey respondents totaled 223 blueberry producers of various production sizes and scope. A majority (61%) indicated that their berries were destined for fresh markets with 33% machine harvested for this purpose. Eighty percent said that they thought fruit quality was the limiting factor for machine-harvested blueberries destined for fresh markets. Many producers had used mechanized harvesters, but their experience varied greatly. Just less than half (47%) used mechanical harvesters for fewer than 5 years. Most respondents indicated that labor was a primary concern, as well as competing markets and weather. New technologies that reduce harvesting constraints, such as improvements to harvest machinery and packing lines, were of interest to most respondents. Forty-five percent stated they would be interested in using a modified harvest-aid platform with handheld shaking devices if it is viable (i.e., fruit quality and picking efficiency is maintained and the practice is cost effective). Overall, the survey showed that blueberry producers have great concerns with labor costs and availability and are open to exploring mechanization as a way to mitigate the need for hand-harvest labor.

Susceptibility of Bunch Grape and Muscadine Cultivars to Berry Splitting and Spotted-Wing Drosophila Oviposition

Fruit splitting is a physiological disorder that produces surface cracks that promote disease and insect damage. The spotted-wing drosophila (SWD), Drosophila suzukii (Matsumura), is a species of vinegar fly that attacks berry crops worldwide, including grapes, and reduces fruit quality and yield. In this study, we tested the susceptibility of various hybrid bunch grapes and muscadines to berry splitting and SWD attack. Ten grape cultivars were harvested in 2016 and 2017, and Thompson Seedless (Vitis vinifera) was purchased locally. Fruit quality traits examined included Brix (soluble solids), total acidity (TA), pH, fruit firmness, and skin break force. Villard blanc and OK392 were the least susceptible to berry splitting (0%). Although muscadines showed the highest fruit firmness, they were also susceptible to splitting, especially Fry Seedless (88% splitting incidence). There were no significant correlations among soluble solids, firmness, and splitting; however, there was a negative correlation between splitting and TA. Pierce’s disease (PD)-resistant and PD-tolerant grapes also appear to be mostly resistant to or highly tolerant of SWD infestation. SWD females do not appear to be able to oviposit in fruit hosts that have a fruit firmness exceeding 300 g/mm. Wounds or splits in the grape epidermis increased reproductive success of SWD by 400%, suggesting that a well-managed vineyard will not host large SWD populations. Vineyards suffering from severe berry damage might provide SWD with a summer fruit host. Overall, PD-resistant hybrids and muscadines are highly adaptive to subtropical climates and are tolerant of this new invasive vinegar fly.

Cutting and Seed Propagation of Chickasaw Plum (Prunus angustifolia)

Chickasaw plum (Prunus angustifolia Marsh.) has the potential to be planted for windbreaks, wildlife, and for human consumption; however, reliable propagation protocols need to be established. Propagation of plants by seed using mechanical scarification treatment and stratification as well as stem cuttings using selected rooting hormone rates for Chickasaw plum were investigated. Seeds and stem cuttings of previous year’s growth were collected in Payne County, Oklahoma. Seed stratification treatments included 0, 30, or 60 d at 3°C. Mechanical scarification employed tip removal from seeds with a nail clipper. Stem cuttings were treated with five IBA rates (0, 100, 1000, 3000, and 7000 mg·L−1) in factorial combination with three collection times (May, August, and October). Scarifying the seed coat did not affect germination percentage. Non-scarified seeds stratified 60 d at 3°C had the highest germination at 31%. The time of year for cutting selection and amount of IBA rooting hormone applied was critical for rooting success. Rooting success was greatest at the highest IBA concentration when cuttings were harvested in May or August (44% and 49%), respectively.

Aerial Root Formation on Winegrape Cultivars after Spring 2007 Freeze Events

Post-budbreak freeze events on 7–8 Apr 2007 were followed by the development of aerial roots on winegrapes later in the spring and continuing through the summer months. Rainfall and relative humidity were much higher than average during the months of May, June, and July following the freeze events. Aerial rooting of grapes has not been previously reported in Oklahoma; therefore, quantitative counts of aerial rooting were performed to determine if there was a relationship between aerial root formation and subsequent vine productivity. Aerial root production varied by scion cultivar and the effect of rootstock was unclear. Only Petit Verdot produced significantly more roots on a rootstock than not. It appears that the formation of aerial roots on grapevines in situ is a complex interaction of freeze injury and subsequent environmental conditions to produce roots. Aerial rooting was likely a sign of injury, but the number of aerial roots produced did not necessarily represent the degree of injury. Few or no roots may be produced when injury or damage is slight, more with moderate injury or damage, and few again when significant injury or damage is sustained.