No abstract

Land was prepared conventionally in early spring for the planting of small seeded legumes. Planting was delayed to allow emergence of weeds. We applied 1,1'-dimethyl-4,4'-bipyridinium salts (paraquat) and planted legumes immediately afterwards. Stage of weed growth, time of herbicide application, rate of chemical applied, and the methods of seeding were variables imposed. Paraquat (plus surfactant) applied at 1.1 and 2.2 kg/ha to emerged weeds prior to the seeding of legumes controlled quackgrass [Agropyron repens(L.) Beauv.] sufficiently to allow excellent establishment of alfalfa (Medicago sativaL.) and birdsfoot trefoil (Lotus corniculatusL.). A paraquat application delayed until yellow nutsedge (Cyperus esculentusL.) was at least 10 cm in height, followed by a disking, controlled the sedge sufficiently to allow legume establishment. For annual weed control, 0.3% kg/ha of paraquat was sufficient. Drilling as a method of seeding gave better legume stands than did surface-seeding techniques.

We applied 1,1′-dimethyl-4,4′-bipyridinium ion (paraquat) to quackgrass (Agropyron repens L. Beauv.) at different stages of growth and subjected these treated plants to different light regimes. After paraquat and light treatment, foliage was removed and the reduction in regrowth was measured as evidence of paraquat movement and its effect on the regenerative potential of the rhizomes. Paraquat or a toxic metabolite moved in quantity from point of leaf application. Sufficient basipetal movement occurred in both the dark and light to significantly affect regrowth. As quackgrass plants matured and developed more foliage, the effect of paraquat treatment increased (i.e., the regrowth capacity of the plants and the regenerative ability of their rhizome buds decreased). A period of darkness (24 hr) after paraquat application and before exposure of treated plants to light did not affect numbers of plants killed but did decrease rate of regrowth. Treated quackgrass foliage showed extensive paraquat injury when placed in light for 48 to 72 hr after treatment; but only parts of treated leaves were killed. Leaving treated foliage intact greatly increased the number of plants killed.