Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2003
Publication Date: 6/1/2004
Citation: Janisiewicz, W.J., Peterson, D.L. 2004. Susceptibility of the stempull areas of the mechanically harvested apples and its control with bicontrol agents. Plant Disease Vol. 88 No. 6 pgs. 662-664. Interpretive Summary: If U.S. growers want to remain competitive in the global market, many aspects of apple technology will have to change soon. Labor shortages and reduction of pesticide use after harvest are major challenges. A new harvester, which uses a new technology to remove apples from trees has shown great potential, but 20% to 57% removed fruits are without stems (stempulls). This may create a potential place of entry for fungi causing decay of fruit after harvest. We evaluated susceptibility of the stem cavity area to blue mold decay on eleven cultivars of mechanically harvested apples with and without stems. On apples with stempulls, cultivars ranged from very susceptible to completely resistant, with most cultivars being resistant to decay or only slightly susceptible. Apples with the stems had little or no decay in all cultivars. Treating fruit with a beneficial bacterium that is used in a commercial biological control product for control of fruit decay, provided a high level of protection against decay even on the most susceptible cultivars. Our research demonstrated that both mechanical harvesting and biological control are developing technologies that can work well together to address critical problems facing apple industry.
Technical Abstract: Labor shortages in the U.S. necessitate the development of a mechanical approach to harvest apples. A new harvester, which uses a rapid displacement actuator on the main scaffolds to remove apples from trees with narrow-inclined trellises, has shown good potential. With this technique, stem loss (stempulls) during harvesting ranges from 20% to 57%, depending on the cultivar. This can create a potential point of entry for pathogens. We evaluated the susceptibility of the stem cavity area, with and without stems, to blue mold decay (Penicillium expansum ) on 11 cultivars of mechanically harvested apples, and tested the effectiveness of the antagonist Pseudomonas syringae (used in BioSave 110) in controlling decay. Fruit with stempulls were more susceptible to blue mold decay than fruit with stems. On fruit with stempulls inoculated with P. expansum and stored for 2 months at 1oC, decay incidence ranged from 0% on `Rubinstar' `Jonagold', `Pink Lady' and `Sun Crisp' to 41% on `Empire'. On other cultivars it ranged from 1.7 to 8.3%. On fruit with the stems, decay did not exceed 3.3%, except on `Gala' (6.6%). P. syringae reduced decay on fruit with stempulls to 3.3% on `Empire' and `Gala', and below that on the other cultivars, with seven cultivars having no decay. Similar trends were observed on fruit stored at 22oC for 14 days, but the incidence of decay was higher. Although mechanical harvesting can predispose the stem cavity to decay in some cultivars, this problem can be alleviated using biological control without resorting to the use of synthetic pesticides.