EFFECT OF NITROGEN ON THE GLYPHOSATE-INDUCED INHIBITION OF RHIZOME BUD GROWTH IN QUACKGRASS (ELYTRIGIA-REPENS)

In experiments conducted under controlled conditions, glyphosate-induc ed inhibition of rhizome bud growth in quackgrass was reduced by incre asing the nitrogen (N) concentration in the nutrient solution from 10. 5 to 210 mg L-1 either 2 or 4 d before foliar application of the herbi cide, and for 7 d after the herbicide treatment. The additional N redu ced the glyphosate-induced inhibition of rhizome growth on the intact plant at the lowest glyphosate dosage (2.8 mug per plant) but had no s ignificant effect at higher dosages. Both the 2- and 4-d high N treatm ents significantly increased the length, dry weight, and water content of the lateral buds by the time the herbicide was applied. They also increased bud growth on the glyphosate-treated plants during the 7 d f ollowing the herbicide application and promoted release of the buds fr om inhibition during a subsequent bioassay of their regenerative growt h on excised, single-node rhizome segments. These effects of N supply interacted significantly with glyphosate dosage, bud position on the r hizome, and duration of incubation. It is postulated that bud growth r esponse to increased N supply may reduce the inhibiting effect of the herbicide by diluting the glyphosate concentration in the bud, or that the additional N may counteract the toxic action of glyphosate on ami no acid metabolism or protein synthesis.