Imazapyr Absorption and Translocation in Northern Red Oak and Red Maple as Affected by Herbicide Formulation and the Adjuvant Methylated Seed Oil

Imazapyr-based herbicides are important in removing deciduous hardwood species from conifer plantations. Imazapyr can be applied as a site preparation (pre-establishment) application or as a postestablishment herbaceous or release application. Herbicide efficacy is dependent, in part, on how much herbicide is absorbed and translocated throughout the target weed species. Herbicide absorption can be strongly influenced by herbicide formulation or tank-mix adjuvants. Little data are available on imazapyr absorption and translocation by woody species. The objective of this research was to compare the absorption and translocation of six experimental formulations of imazapyr to a commercial formulation, Chopper®, with and without methylated seed oil (MSO), in northern red oak (Quercus rubra L.) and red maple (Acer rubrum L.). Saplings of both species were grown in the greenhouse until they reached a height of approximately 1 m. Trees were blocked according to size, and treatments were randomly assigned within blocks. For the absorption study, five leaves were selected per plant and received two 1-μL drops of 14C-imazapyr-labeled solution. Leaves were rinsed at 2, 8, 24, 72, and 144 h after treatment (HAT). Absorption was quantified as 14C imazapyr that was not collected in the rinse solution. All experimental formulations that were tank-mixed with MSO increased absorption on oak compared to Chopper+MSO. Not all experimental formulations increased absorption in maple, and absorption data were highly variable. Absorption continued for at least 72 HAT in both species for most formulations. For the translocation study, one leaf was treated with two 1-μL drops of 14C-imazapyr-labeled solution. The leaf was rinsed at 144 HAT, and the plant was harvested and divided into sections: above treated leaf, treated leaf, below treated leaf, and roots. The majority (52–91 %) of the applied imazapyr remained in the treated leaf. More imazapyr was translocated from the leaf of red oak than red maple. Translocated 14C accumulated in the tissue above the treated leaf (3–13 % of absorbed) and in the roots (3–34 %). Including the adjuvant MSO and optimizing the herbicide formulation increased the absorption of imazapyr in red maple and northern red oak.