Germination, emergence, growth, ecotypes and control of Carex appressa R. Br. (tussock sedge)

Abstract

Germination of seeds of Carex appressa R.Br. (tussock sedge) collected in 1989 and 1990 from Bigga, Boorowa and Kerrs Creek, New South Wales, Australia, stored in a laboratory and germinated annually in 45-day tests, declined from an initial 75–90% in year 1 to 0.5–14% in years 10 and 11. The germination of seeds collected from Bigga and Boorowa in 1991 declined from 90–91% in year 1 to 12–61% in year 9. This decline was best described by generalised logistic curves (Bigga) and exponential curves (Boorowa). Most seeds that failed to germinate were shown to be non-viable by the tetrazolium test. Rate of germination declined with seed age, so that days for 50% of final germination percentage increased from 8 days for 1 year-old seeds to >40 days for 11-year-old seeds. Of 8–11-year-old seeds that germinated between days 45 and 140, 62–70% had deformed seedlings. Germination of seeds buried in the soil for 0.5–2.7 years was lower than that of the same seed stored in the laboratory. Germination of seeds buried at 5 mm (19%) was lower than that of the same seeds buried at 40 mm (50%). Almost all the decline in germination occurred in the first 6 months of burial. Increased depth of sowing reduced emergence (%), height of the shoot and length of the primary root and increased the time taken for emergence and length of the mesocotyl. The maximum depth C. appressa seedlings could emerge from was 44 mm. Growth of C. appressa seedlings was slower than that of pasture species and responded to nitrogen and nitrogen + phosphorus and/or sulfur but not to phosphorus and/or sulfur. Differences were recorded in the morphology of plants grown from seeds collected from various locations and grown in the 1 environment at Orange, New South Wales. Control of C. appressa was achieved by draining, slashing and removing litter, applying glyphosate, surface-sowing pasture species and topdressing with superphosphate. Five years after sowing, the foliage cover of legumes and grasses on the best treatment was 71% and that of C. appressa 2%, a substantial decline from the original 81% infestation. The best technique for control of C. appressa on infested creek flats suitable for pasture production would be to drain, plough and bury seeds below 44 mm and then sow pastures with superphosphate. Where ploughing is not possible, drainage, burning to remove foliage, spraying with glyphosate and surface-sowing pastures with superphosphate would be successful. In both situations, long-term control can be achieved by heavy grazing for short periods only when the soil is firm and removing re-infesting plants by annual spot spraying.