INFLUENCE OF GLYPHOSATE AND CROP COMPETITION ON QUACK GRASS CONTROL AND CROP PRODUCTIVITY

A field experiment with glyphosate (n-phosphonomethyl glycine), tillage, and cropping in late summer and in the next spring, included winter rye (Secale cereale L.) and oats (Avena sativa L.) competing with dense established quack grass (Agropyron repens (L.) Beauv.). Foliage sprays of glyphosate [2.8 kg/ha (2.5 lb/A) in water (281 liters/ha) (25 gal/A), applied at 1.76-kg/cm2 (25 psi) pressure] before tillage, reduced grass forage and rhizomes of the dense stands by 90% or more. Late summer spraying was as effective as spring spraying. Some rhizomes had healthy portions, after death, of proximal and distal ends. One tillage in late summer plus one in the next spring reduced quack grass forage weight more than did tillage twice in the late summer or twice in the spring. Oat plots with their second tillage delayed until spring contained 68% less quack grass than the unseeded controls, but forage and grain yields of the spring-seeded oats, and of the rye seeded before winter, were not significantly different. These yields from sprayed plots were approximately double those from unsprayed plots. Without spraying, oats competed more effectively with quack grass than spring-seeded winter rye, but both produced well on sprayed land. One spraying did not eradicate quack grass but appears to avoid the need for summer fallow to control it.