The effect of 2,4-D on the respiration rate and ethylene production of Bartlett pears and Red Delicious apples Public Deposited

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  • After nearly 20 years of commercial use in orchards without apparent tree injury in Oregon and Washington, 2,4-D [(2,4-dichlorophenoxy) acetic acid] was reported in 1970 to cause injury to apple and pear trees in Washington. In the early 1970's, there was widespread concern among growers, researchers, and processors in the Hood River Valley of Oregon that 2,4-D might cause premature ripening of pears. Studies were conducted in 1971 to: (1) document the disappearance of 2,4-D from orchard soils; (2) analyze for 2,4-D residues in developing apple and pear fruits throughout the season; and (3) determine if 2,4-D, when properly applied to Red Delicious apple and Bartlett pear orchards, alters the ripening process of mature fruit. Applications of 2,4-D were made at 0, 2.24, and 4.48 kg/ha. Experimental sites were in apple and pear orchards in the upper and lower Hood River Valley near Hood River, Oregon. Soil samples were collected at 5-cm increments to a depth of 30 cm at 0, 14, 21, and 28 days following treatment. Fruit was harvested weekly from the juvenile through the mature growth stages and analyzed for possible 2,4-D residues. Each sample was hydrolyzed with NaOH to remove 2,4-D residues. The 2,4-D aliquot was then acidified and extracted with ethyl ether. Purification of the extract was accomplished by passing it through a basic aluminum oxide column. Following esterification with a 5-ml aliquot of 11% BF₃ methanol, the methyl ester of 2,4-D was partitioned into 1 ml benzene and analyzed on a Varian 1200 gas chromatograph equipped with a microcoulometric detector. Ethylene and CO₂ samples were collected from respiring apples and pears in a continuous air flow respiration chamber to determine if 2,4-D would cause subtle physiological or biochemical changes in the ripening process. CO₂ evolution was monitored with a Beckman infrared CO₂ analyzer. Samples for ethylene analysis were withdrawn in hypodermic syringes from the exhaust tube and analyzed in an Aerograph Model 600-D ionizing gas chromatograph. The degradation of 2,4-D from soil samples was rapid in these experiments. Approximately 98% of it was lost after 21 days. At 28 days, no detectable levels of 2,4-D (sensitivity 0.02 ppm) were found in any samples. The 5-10 cm zone was the maximum depth at which 2,4-D was detected in the soil profile. No detectable 2,4-D residues were found in any of the apple and pear fruit samples. When orchard location (upper or lower Hood River Valley), gas sampling time, and application rate were statistically analyzed using a three-way factorial analysis, no significant differences (P = .05) were found to exist as a result of treatment level in the apple or pear orchards.
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