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Leaching Behavior of Two Pendimethalin Formulations in a Soilless Growing Medium

Published online by Cambridge University Press:  20 January 2017

Jeffrey Derr*
Affiliation:
Virginia Tech, Hampton Roads AREC, 1444 Diamond Springs Rd., Virginia Beach, VA 23455
Lori Robertson
Affiliation:
Virginia Tech, Department of Plant Pathology, Physiology, and Weed Science, Price Hall, Blacksburg, VA 24061
Elizabeth Watson
Affiliation:
Virginia Tech, Department of Biochemistry, 350 Litton Reaves Hall, Blacksburg, VA 24061
*
Corresponding author's E-mail: jderr@vt.edu
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Abstract

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Pendimethalin is commonly applied for PRE weed control in container nursery production. Field and laboratory trials were conducted to determine herbicide effectiveness and leaching of two pendimethalin formulations in pine bark, the primary component used in the growing medium of container-grown plants in the South. The microencapsulated (ME) formulation of pendimethalin gave lower control of southern crabgrass and leached deeper than the emulsifiable concentrate (EC) formulation in pine bark. The EC formulation controlled southern crabgrass 93% compared with only 70% with the ME formulation at 4.48 kg ai ha−1. After applying 3.4 kg ai ha−1 pendimethalin and 17.8 cm of irrigation water, the ME formulation showed greater leaching into the 3- to 6- and 6- to 9-cm depths than the EC formulation on the basis of a southern crabgrass bioassay. Using a microwave extraction method, only 0.91 mg kg−1 pendimethalin was found in the 3- to 6-cm pine bark depth compared with 4.0 mg kg−1 for the ME formulation. Below the 6-cm depth, no pendimethalin was detected when the EC formulation was applied, but 0.5 ppm was found for the ME formulation. No pendimethalin was detected in effluent collected from irrigation water for the EC; however, 3.0 mg kg−1 was collected from leachate for the ME formulation. Pendimethalin ME is leaching much deeper than the EC formulation in the pine bark profile, which results in lower weed control. This extensive leaching of ME formulation may be due to capsule movement with the irrigation water, combined with a delayed release of pendimethalin, which then binds to the pine bark much lower in the container profile.

Information

Type
Soil/Air/Water
Copyright
Copyright © Weed Science Society of America