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CLIMATIC VARIATION AND GROWTH OF HOLY THISTLE (SILYBUM MARIANUM GAERTN.)

KHAN BAHADAR MARWAT AND MUHAMMAD AZIM KHAN

Abstract: There is an increasing interest in weed suppression through manipulation of crop density. To test this hypothesis as to how growth of Holy thistle (Silybum marianum) is affected by environmental conditions, experiment was conducted in RCBD with split plot arrangements by sowing four seed rates of wheat (100, 120, 140 and 160 kg ha^-1) in main plots and seven S. marianum densities (0, 3, 6, 9, 12, 15 and 18 m^-2) in sub-plots. Increasing seed rate of wheat greatly suppressed the growth of S. marianum during year 1 and had no effect on S. marianum growth in year 2 due to higher rainfall and low temperature which favoured the growth of S. marianum. With the increasing density of either species, the seed production plant^-1 of S. marianum decreased but the magnitude of seed reduction was dependent on seed rate, S. marianum density and year effect. Thus seed rate and weed density did not give accurate prediction to estimate the yield losses and competitiveness of weed. Hence other factors like rainfall and temperature should also be considered while developing a model for crop/weed competition. Optimum seed rate (120 kg ha^-1) of wheat could contribute to a strategy to reduce yield losses and to prevent this weed from seed production in long-term weed management. However, this approach can be used as a part of integrated weed management.

Department of Weed Science, NWFP Agricultural University Peshawar, 25130, Pakistan

Correspondence Author's E-mail: ahmadzaipk@yahoo.com