Oxygenated Phosphine Fumigation for Control of <I>Nasonovia ribisnigri</I> (Homoptera: Aphididae) on Harvested Lettuce

Abstract

Low temperature regular phosphine fumigations under the normal oxygen level and oxygenated phosphine fumigations under superatmospheric oxygen levels were compared for efficacy against the aphid, Nasonovia ribisnigri (Mosley), and effects on postharvest quality of romaine and head lettuce. Low temperature regular phosphine fumigation was effective against the aphid. However, a 3 d treatment with high phosphine concentrations of > or = 2,000 ppm was needed for complete control of the aphid. Oxygen greatly increased phosphine toxicity and significantly reduced both treatment time and phosphine concentration for control of N. ribisnigri. At 1,000 ppm phosphine, 72 h regular fumigations at 6 degrees C did not achieve 100% mortality of the aphid. The 1,000 ppm phosphine fumigation under 60% O2 killed all aphids in 30 h. Both a 72 h regular fumigation with 2,200 ppm phosphine and a 48 h oxygenated fumigation with 1,000 ppm phosphine under 60% O2 were tested on romaine and head lettuce at 3 degrees C. Both treatments achieved complete control of N. ribisnigri. However, the 72 h regular fumigation resulted in significantly higher percentages of lettuce with injuries and significantly lower lettuce internal quality scores than the 48 h oxygenated phosphine fumigation. Although the oxygenated phosphine fumigation also caused injuries to some treated lettuce, lettuce quality remained very good and the treatment is not expected to have a significant impact on marketability of the lettuce. This study demonstrated that oxygenated phosphine fumigation was more effective and less phytotoxic for controlling N. ribisnigri on harvested lettuce than regular phosphine fumigation and is promising for practical use.

Oxygenated Phosphine Fumigation for Control of <I>Epiphyas postvittana</I> (Lepidoptera: Tortricidae) Eggs on Lettuce

“…After phosphine injection, all jars including controls were held at 2ЊC for 40, 48, 56, 64, and 72 h to complete fumigation treatments. At the end of each treatment duration, phosphine concentrations in the respective jars were measured with a HewlettÐPackard 6890N gas chromatograph (Agilent Technologies, Santa Clara, CA) equipped with a ßame photometric detector using the procedures described previously (Liu 2012). The 1.6% phosphine sample was diluted in series in foil bags to serve as standards for calibrations.…”

“…Three-day phosphine fumigations of lettuce under 60% O 2 with and without CO 2 absorbent were conducted in 442-liter fumigation chambers (Liu 2012) at 2ЊC in walk-in coolers to demonstrate injuries associated with the long fumigation and effectiveness of CO 2 absorbent in preventing such injuries. The two fumigation treatments with the same phosphine dose were conducted in two chambers, one with CO 2 absorbent and the other without CO 2 absorbent.…”

“…The phosphine sample was released into each chamber from a 3.8-liter sample cylinder equipped with a pressure gauge. The volume of phosphine sample was calculated based on differential pressure readings on the sample cylinder as described in an earlier study (Liu 2012). The pressure inside each chamber was balanced to ambient air pressure by allowing air in the chamber to ßow into a 3,700-cm 2 empty foil bag connected to each chamber.…”

“…Fumigation with cylindered pure phosphine free of ammonia has been used successfully at low temperatures to control some pests on fresh fruits in Chile Horn 2004, Horn et al 2005) and has potential to be a practical alternative to methyl bromide fumigation on fresh commodities. Oxygenated phosphine fumigation (fumigation in oxygenenriched atmosphere) was found to have signiÞcantly higher efÞcacy and shorter treatment times than regular phosphine fumigation against any given life stage or insect species tested and may be more suitable for fresh commodities than regular phosphine fumigation (Liu 2011(Liu , 2012.…”

“…Even though cylindered phosphine is pure and free of ammonia, longer treatment of 3 d for controlling more tolerant insects such as the aphid Nasonovia ribisnigri (Mosley) (Homoptera: Aphididae) still causes injuries to both romaine and iceberg lettuce (Liu 2012). Shorter (Յ24 h) phosphine fumigation at low temperature is effective in controlling western ßower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae), without any negative impact on postharvest quality of lettuce and other commodities (Liu 2008).…”