DENSITY DEPENDENT INTERACTIONS BETWEEN CLEAVERS (Galium aparine) AND WHEAT (Triticum aestivum) PLANTED AT DIFFERENT TIMES

Investigations regarding competitive effects of five Galium aparine density levels (0, 18, 36, 54 and 72 m-2) on the yield and yield related traits of wheat planted at three sowing times were made in field trials conducted at the Agronomic Research Area, University of Agriculture, Faisalabad, Pakistan during winter 2005/06 and 2006/07. Maximum grain yield of 5480 and 5395 kg ha^-1 was obtained in 2005/06 and 2006/07, respectively from weed free wheat. While G. aparine density of 18 plants m^-2 did not cause significant yield reduction over control. Wheat growth and yield determinants like number of spike bearing tillers, grains per spike, 1000-grain weight and grain yield were significantly reduced by increasing G. aparine density above 18 m^-2. Wheat grain yield loss varied between 4 to 32% with weed density ranging from 18 to 72 plants m^-2 in each year. Sowing of wheat on 7th November proved to be helpful in reducing crop yield losses due to G. aparine infestation. G. aparine per plant dry weight and seed production were suppressed with delayed sowing and increasing G. aparine densities in the presence of crop. On the basis of these results we can propose that wheat should be planted in early November to get bumper yields and the option of chemical herbicides to control G. aparine at its density beyond 18 plants m^-2 should be exploited.