Clopyralid Use in Strawberries (Fragaria x ananassa Duch.) Grown on Plastic Mulch

摘要

Experiments were conducted in North Carolina in winter/spring 1992,1993, and 1994 to determine crop tolerance, weed response, and clopyralid residue levels in fruit of 'Chandler' strawberry plants treated with clopyralid. Clopyralid at 0.07,0.14,0.20, or 0.28 kg ai ha~(-1) applied POST over strawberry plants and vetch resulted in 100% control of vetch species, 49 to 83% control of black medic, and less than 6% crop injury. As a comparison, 2,4-D at 0.84 kg ai ha~(-1) applied POST at 5 to 10% strawberry bloom resulted in 50% control of black medic and 48 to 73% crop injury, while 2,4-D at 0.84 kg ai ha~(-1) applied POST to 7- to 9- and 9- to 10-leaf strawberries resulted in 5 to 22% crop injury and no adverse affect on strawberry yield. Single applications of clopyralid at 0.07, 0.14, or 0.28 kg ai ha~(-1) applied POST to weed-free strawberries at the 5- to 6-, 6- to 7-, 9- to 10-, or 12-to 14-leaf stage caused less than 6% injury and did not adversely affect strawberry yield. In 1993 with preharvest intervals (PHI) of 39, 66, and 101 d after treatment all clopyralid residue levels in strawberry fruit were below the detectable level of 0.3 parts per billion (ppb). In 1994, with PHI of 30, 59, and 87 d after treatment trace clopyralid residues were found in strawberry fruit with a range from 0.25 to 1.9 ppb, with a level of detection of 0.2 ppb.