STUDY OF PRE AND EARLY POST EMERGENCE ALLELOPATHIC EFFECTS ON SELECTED WEEDS OF SEVERAL SORGHUM [Sorghum bicolor (L.) Moench.] AND PEARL MILLET (Pennisetum glaucum L.) CULTIVARS IN ZIMBABWE
Allelopathy has been identified as potentially a cost effective, natural weed control method which could be exploited by smallholders who have little access to herbicides. The objective of this study was to investigate the potential of sorghum and pearl millet cultivars for their allelopathic effect against several weeds. Water extracts of the stems root and leaves of twelve sorghum and pearl millet cultivars were screened for their ability to suppress germination and dry weight of blackjack (Bidens pilosa L.), upright starbur (Acanthospermum hispidium L.) and goose grass [Eleusine indica (L.) Gaertn)] and by the addition of their plant material to soil under laboratory and glasshouse conditions. A randomized complete block design with three replicates was used and the experiment was repeated twice over time. Results showed that there was a significant (P < 0.01) effect of sorghum and pearl millet cultivars on germination / emergence and dry weight of goose grass and blackjack. It was established that sorghum and pearl millet cultivars has no significant (P > 0.05) effect on germination of upright starbur and pearl millet landrace. However upright starbur dry weight was significant affected by sorghum and millets plant residues. From this study it can be concluded that all the sorghum and pearl millet cultivars reduced the germination and growth of goose grass and blackjack. Upright starbur was independent of the extracts applied. It can be concluded that incorporation of sorghum and millet residues can work as a tool in the integrated weed management for the rural farmers in Zimbabwe.