Effect of shading on the growth of some common weeds of the semi-arid tropics.
Shade tolerance of 7 common weeds of the semiarid tropics was studied in the 1978-9 wet seasons using 4 or 5 shading levels in the range 0-10% of incident sunlight. Shading at the highest rate reduced plant ht. of Celosia argentea and Tridax procumbens, LAI of Digitaria ciliaris and Dactyloctenium aegyptium and DM production of D. ciliaris, D. aegyptium and Acanthospermum hispidum to 30, 20-30 and 20%, resp., of those of unshaded plants. Plant ht. of Cyperus rotundus and Amaranthus viridis was little affected, but shading markedly reduced LAI and DM production. Shading markedly reduced seed production in annual weeds and tuber production in C. rotundus. In general, dicotyledonous weeds were less sensitive to shading than were monocotyledonous weeds. It weas concluded that substantial weed suppression could be achieved by manipulating crop canopies. The agronomic significance of these results is discussed.