Biology and control of bpomus pectinatus thunb

Abstract

Investigations into the biology and control of the annual grassy weed Rromus peatinatus Thunb. were conducted at the National Plant Breeding Station, Njoro, Kenya, from 1982 to 1984. R. peatinatus is described and, in the tradition of other Bromus sp. of similar morphology, the common name Kenya Chess is proposed for B. peatinatus. Pot growth of B. peatinatus was influenced by soil type and microclimate, but not by seed origin. B. peatinatus was germinated and grown in ammended and untreated soils ranging in pH from 3.05 to 8.13. Soils with a pH near 3 could not support growth or germination of B. peatinatus. B. peatinatus grew best on a soil of pH 6.55 and when soil pH influenced germination the optimum soil pH was 6.0. Out-of-doors grown R. peatinatus matured earlier and had fewer culms than plants grown in the shadehouse or glasshouse. Exposure to light during germination, inhibited the germination of R. peatinatus seeds. Germination of B. peatinatus seed was most rapid at a 17 C temperature. Prechilling or preheating seeds did not promote germination of dormant B. peatinatus seeds. Germination of dormant B. peatinatus seeds was enhanced by seed hull removal or pricking the lemma or removing the rachilla segment. Germination of B. pectinatus seed in the soil was unaffected by depth of burial, whereas, emergence was reduced to 35, 19, 11, 4 and 0% from depths of 0, 1, 2, 4 and 8 cm, respectively. There was a relationship between field emergence of B. pectinatus and the precipitation pattern. After-harvest germination of B. pectinatus seed indicated that there was an innate dormancy in hulled seed which persisted for 8 months. The innate dormancy was mainly induced by the seed hull, but was also induced within the caryopsis itself. Field measurements were used to develop an equation which related yield loss in wheat with B. pectinatus infestation. Delayed sowing of wheat and barley into a B. pectinatus infested site resulted in yield reductions that were correlated with length of delay. Replacement series studies were conducted using varying proportions of wheat: B. pectinatus and rapeseed: B. pectinatus. Varying the proportions resulted in growth changes in the plants. B. pectinatus maturation was delayed when grown in a mixture. Rapeseed was unaffected by B. pectinatus interference. A spatial interference study determined that B. pectinatus interfers with wheat mainly above ground. The herbicides isoproturon, pendimetha1in and oxadiazon were found to be ineffective against B. pectinatus. The herbicides tria11ate, ch10rsu1furon, metribuzin, trif1ura1in and EPTC achieved limited control of B. pectinatus. Superior control of B. pectinatus was achieved using f1uazifop-buty1 at 0.25 kg/ha and fenthiaprop-ethy1 at 0.12 kg/ha, in rapeseed.