Increased crop density reduces weed seed production without increasing screenings.

Results from a series of related field trials confirm that Western Australian crop varieties do not increase screenings with increased seeding rates contrary to the general belief held by farmers. This has management implications for weed control as increasing the crop density can substantially reduce weed growth and seed production in the absence of in-crop herbicides. In one trial, seeding rates of up to 400 kg ha of 4 cereals (oats, barley, wheat and triticale) were investigated as a management tool to control annual ryegrass and wild radish. All 4 cereals were successful in reducing weed seed production to manageable levels at high seeding rates. The yields of both wheat and triticale decreased when seeding rates increased, due to the extremely dry finish to the season in 1998, but only triticale increased screenings. The earlier maturing oats and barley were unaffected. Other trials investigating seeding rates and/or seeding pattern and row spacing with different varieties of wheat have corroborated the uniformity of screenings with seeding density.