Quizalofop-P-Ethyl Herbicide Interactions in Accase-Resistant Rice Production

A field study was conducted in 2015 and 2016 at the H. Rouse Caffey Rice Research Station (RRS) to evaluate mixture interactions of quizalofop and ALS-inhibiting herbicides. Quizalofop was applied at 120 g ai ha-1. Mixture herbicides included penoxsulam at 40 g ha-1, penoxsulam plus triclopyr at 352 g ha-1, halosulfuron at 53 g ha-1, bispyribac at 34 g ha-1, orthosulfamuron plus halosulfuron at 94 g ha-1, orthosulfamuron plus quinclorac at 491 g ha-1, imazosulfuron at 211 g ha-1, and bensulfuron at 43 g ha-1. All ALS herbicides mixed with quizalofop indicated antagonistic responses for weedy rice or barnyardgrass control at either 14 or 28 days after treatment (DAT). At 28 DAT, quizalofop mixed with penoxsulam or bispyribac controlled barnyardgrass 33 to 38%, compared with an expected control of 91 to 92%. A study was conducted at the RRS to evaluate interactions of quizalofop applied in mixtures with contact herbicides. Quizalofop was applied at 120 g ha-1. Mixture herbicides included carfentrazone at 18 g ha-1, propanil at 3360 g ha-1, saflufenacil at 25 g ha-1, or thiobencarb at 3360 g ha-1. Propanil severely antagonized quizalofop activity on weedy rice and barnyardgrass at all evaluations. At 28 DAT, barnyardgrass treated with quizalofop mixed propanil indicated an observed control of 16%, compared with an expected control of 93%. A study was conducted at the RRS evaluating sequential applications of quizalofop at 120 g ha-1 and propanil plus thiobencarb at 672 g ai ha-1. A prepackage mixture of propanil plus thiobencarb was applied for each timing treatment when ACCase-R rice was at the 2- to 3-leaf growth stage (day 0). Application timing treatments consisted of quizalofop applied at 7, 3, and 1 days before (DBPT) and after (DAPT) the propanil plus thiobencarb application at day 0. Additionally, quizalofop was applied alone and in a mixture with propanil plus thiobencarb at day 0. Quizalofop activity was reduced on weedy rice and barnyardgrass when applied at 1 and 3 DAPT or mixed with propanil plus thiobencarb at day 0; however, quizalofop activity was not reduced when applied before propanil plus thiobencarb.