Poast / sethoxydim

WSSA Resistance Group: 1

Crop/non-crop registration: Soybeans, peanuts, alfalfa, beans, peas, tomatoes, cucumber, broccoli, stone fruits, sethoxydim-resistant corn

Sensitive weeds: Annual grass species; volunteer corn, wheat, barley; quackgrass.

Application method: POST- when grasses actively growing 1-6 leaf stage, quackgrass 1-3 leaf stage.

Absorption & Translocation: Rapidly absorbed by both roots and foliage and is generally rainfast by 1 hr after application;sethoxydim is systemic and is translocated via both xylem and phloem (primarily) to meristematic regions of roots, rhizomes and shoots where it accumulates; however, translocation is relatively slow.

Mode of Action: Inhibition of lipid formation.

Metabolic pathway inhibited: Inhibits acetyl-CoA carboxylase (ACCase), the enzyme catalyzing the first step in de novo fatty acid synthesis; inhibition of fatty acid synthesis presumably blocks the production of phospholipids which are essential components of cell membranes.

Basis of Selectivity: Metabolized by tolerant species (and/or insensitivity of ACCase).

Symptoms: Cessation of growth within 2-3 days after application; growing tissue in the nodes and buds become necrotic, young leaves are first affected and turn yellow (within 1-3 wks) and then brown, depending on growing conditions and crop competition; leaf sheaths become brown and mushy at or just above their point of attachment to the node; older leaves show yellowing, light purpling and browning; susceptible plants are typically dead within 2-4 weeks and those not completely dead may show excessive tillering.

Residuality: Essentially none; short (< 1month).

Toxicity: Oral LD50 = 2676-3124 mg/kg - slightly toxic (POAST PLUS = >2200 mg/kg- slightly toxic).

Additional comments: Rainfall within 1 hour after application may reduce efficacy; if treated grasses are stressed (lack of moisture, flooding, prolonged cool temperatures) control will be delayed or reduced; since there is no residual activity, a second application and/or cultivation may be necessary to control a new flush of weeds; use flat fan nozzles and add suggested adjuvant (e.g. MERGE) to spray mixture; follow label instructions as to how and when to apply broadleaf herbicides on same area.

Image above: Grass weed control with sethoxydim (POST) 10 days after application (DAP). Note that stems of grass weeds break off at the soil surface when pulling on plants.