The interaction of soyabean [Glycine max (L.) merill] and upright starbur (Acanthospermum hispidum)
1990
Chivinge, O.A. (University of Zimbabwe, Harare (Zimbabwe). Dept. of Crop Science)
The objective of this study was to determine the effect of upright starbur on soyabeans when the weed was planted at the same time and after crop emergence. Soyabean plants seeded at the same time as the weed had a prolonged vegetative growth, and consequently a longer growth duration by 15 days compared to those planted 11 and 22 before the weed. The same plants also failed to form branches, had thin weak stems and pale leaves. The weight of 100 seeds revealed that the weed was most aggressive when the crop and the weed were planted at the same time. In general there were large reductions in the yield components between the crop planted at the same time as the weed and those planted 11 days before, compared to those planted at 11 and 22 days before the weed. The most sensitive parameter to competition from the weed was pod dry weight. Increases in height were observed when the crop was planted with and before the weed, irrespective of the time of planting. Plants of upright starbur, planted at the same time as soyabeans grew vertically as long as the crop was shorter. When the crop grew taller than the weed, the weed plants assumed a semi-lodged position. All growth parameters and seed yield of the weed were drastically reduced due to interference from the crop. The results from this study suggest that soyabean yields are unlikely to be reduced by upright starbur provided that the seedbed is clean at planting and control measures keep the weed populations low in the high potential areas, where moisture is unlikely to be limiting
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