Conducted by EMG team: Areefa Tietis, Cynthia Coetzee, André Van Wyk
Lead researcher Siya Myeza.
Supervised by: Noel Oettle
Start date: 22 September 2014
Amsinckia is an invasive alien herbaceous plant that thrives in disturbed and more fertile areas. It is winter growing and flowers and sets seed in the spring months of August and September, and with the seed maturing in October. Its presence is undesirable because it is invasive and thus displaces indigenous plants, and it is unpalatable for livestock, especially later in the spring when its hairy leaves irritate the mouths of grazing animals. Its thorny seed pods are readily transported and distributed in the wool of sheep.
Over the past four spring seasons control in the form of uprooting has been implemented in three areas and has proven effective in turning the tied on the spread of Amsinckia, and has even contained it effectively in some areas where follow-up has been done consistently for all four years. In the late summer and autumn of 2014, four camps were grazed by flocks of sheep for a carefully managed number of days. It is known that the presence and movement of sheep is a contributing factor to the spread of Amsinckia, and it is likely that the movement of the sheep within these camps will have spread seed. The disturbance caused by their hooves would have disturbed the soil surface and the concentration of their manure in certain areas of the camps will have created more fertile conditions that favour the growth of the plant, enabling it to out-compete indigenous plants.
Uprooting and leaving the dead Amsinckia plant material lying on the site has been done in the past on Avontuur, with significant impact in some areas (but less so in others). In 2014 and 2015 uprooted plant material was removed from the most densely invaded area in the Biodiversity Corridor Camp. This was done for two reasons:
1. The invaded area has been utilised by sheep as a resting area for many years, and thus has been heavily fertilised. The abundance of soil nutrients causes the Amsinckia to grow vigorously and outcompete other plant species, resulting in a virtual monoculture of Amsinckia over a large area. Removal of green plant material removes a significant amount of material that would otherwise be recycled and maintain the high nutrient levels. The green Amsinckia could be composted and the compost used for intensive horticultural purposes in a contained area where management of weeds is undertaken on a regular basis.
2. Initial results from the experimental plots described in this paper indicated that uprooting and removal of plant material resulted in far more effective control than merely uprooting and leaving the material in situ.
Amsinckia seed is known to remain viable for up to 2 years, and thorough control with annual follow-up for at least 3 years appears to be essential, not least because individual plants tend to be overlooked each year. Furthermore, there are different views or “theories” regarding viability of seed following uprooting: on the basis of their observations in the field, some land managers believe that the seed continues to mature and produce viable seed following uprooting. An alternative theory (supported by the literature) is that plants may have mature seed at their base whilst still appearing immature at their growing tips, where the flowers typically appear.
This experiment will enable comparison of the effectiveness of different methods of Amsinckia control (uprooting and removing plant material, uprooting and leaving plant material, herbicide application and brush cutting), and will also provide land managers with insight in terms of cost effectiveness and labour intensity.
Initial results after one year of monitoring indicate significantly different impact. The control treatments have been repeated one year later, and the finding have already informed management practice. Further observation and treatment will be undertaken in the coming years.
We will post the detailed results on this site in the near future.