Fewer postharvest technologies are available for use on organic than conventional fruits and vegetables. Even though biopesticides are perceived as likely candidates for postharvest use on organic produce, only some biopesticides will be approved as organic compounds for various reasons. An example is the definition of a biopesticide used by regulatory agencies such as the EPA which includes compounds that will not be considered organically acceptable. Fortunately, there are other existing or new technologies that could be acceptable on organic fruits and vegetables. Some examples are hot water immersion treatment or a hot water rinsing and brushing, new innovative controlled atmosphere techniques, alternative sprout control agents, naturally occurring volatiles and biofumigants. More research is needed on each of these technologies, both singly and in combination with each other.
Robert K. Prange, Ali A. Ramin, Barbara J. Daniels-Lake, John M. DeLong, and P. Gordon Braun
P. Gordon Braun, Keith D. Fuller, Kenneth McRae, and Sherry A.E. Fillmore
This study evaluated the effects of pre-plant treatments: deep ripping (DR), fumigation (F), deep ripping plus fumigation (DRF), deep ripping plus hog manure compost (DRC), and deep ripping plus fumigation plus hog manure compost (DRFC) in comparison with a non-treated control (NTC) on shoot and root performance of ‘Honeycrisp’ apple trees on M.4 rootstocks in an old orchard site with apple replant disease (ARD). Cylindrocarpon spp., Pythium spp., and Pratylenchus penetrans Cobb, all potential agents of ARD, were present in the orchard soil. Fine-root numbers (1 to 2.9 mm diameter) were significantly greater in the DRC and DRFC treatments than the DR treatment. After 6 years, trunk cross-sectional area (TCSA) and yield were largest for the DRFC treatment followed closely by F. The DR treatment had no effect on TCSA, yield, or yield efficiency when applied alone compared with the NTC. Contrast analysis demonstrated that F was significantly better than non-F for yield in all years and TCSA and yield efficiency in 2007. Also, there was a significant interaction between DR and F treatment in 2005 that significantly reduced yield in the DRF treatment. Contrast analysis showed that compost had a significant positive effect on yield in all three production years and TCSA and yield efficiency in 2007. Yield efficiency in the third production year was largest for F, DRC, and the DRFC treatments. Nutrient analysis revealed that soil phosphorus concentrations in compost-treated plots were double those in other treatments. High phosphorus content of compost may have contributed to the amelioration of ARD symptoms. This study found that in 2007, soil fumigation alone, as conventionally used for ARD control, and composted hog manure were equally effective in increasing yield and yield efficiency of apple trees planted in an ARD soil. The DRFC treatment was the overall best treatment in all years.
Ali A. Ramin, P. Gordon Braun, Robert K. Prange, and John M. DeLong
Biofumigation by volatiles of Muscodor albus Worapong, Strobel & W.M. Hess, an endophytic fungus, was investigated for the biological control of three postharvest fungi, Botrytis cinerea Pers., Penicillium expansum Link, and Sclerotinia sclerotiorum (Lib) de Bary, and three bacteria, Erwinia carotovora pv. carotovora (Jones) Bergey et al., Pseudomonas fluorescens Migula (isolate A7B), and Escherichia coli (strain K12). Bacteria and fungi on artificial media in petri dishes were exposed to volatiles produced by M. albus mycelium growing on rye seeds in sealed glass 4-L jars with or without air circulation for up to 48 hours. The amount of dry M. albus–rye seed culture varied from 0.25 to 1.25 g·L–1 of jar volume. Fan circulation of volatiles in jars increased efficacy and 0.25 g·L–1 with fan circulation was sufficient to kill or suppress all fungi and bacteria after 24 and 48 hours, respectively. Two major volatiles of M. albus, isobutyric acid (IBA) and 2-methyl-1-butanol (MB), and one minor one, ethyl butyrate (EB), varied in their control of the same postharvest fungi and bacteria. Among the three fungi, IBA killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 40, 25, and 45 μL·L –1, respectively. MB killed or suppressed S. sclerotiorum, B. cinerea, and P. expansum at 75, 100, and 100 μL·L –1, respectively. EB was only able to kill S. sclerotiorum at 100 μL·L –1. Among the three bacteria, IBA killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 5, 12.5, and 12.5 μL·L–1, respectively. MB killed or suppressed E. coli (K12), E. carotovora pv. carotovora, and P. fluorescens at 100, 75, and 100 μL·L–1, respectively. EB did not control growth of the three bacteria. This study demonstrates the need for air circulation in M. albus, MB, and IBA treatments to optimize the efficacy of these potential postharvest agents of disease control.