Weed control experiment
Our weed control experiment aims to better understand the effects of 4 different weed treatments, immediately following a burn. The main target weeds are illustrated as our introduced plants, and all are pasture plants that grow immediately over the farm fence.
The weed control methods (or treatments) are:
- Scorching with a gas-fueled torch
- Spraying with Roundup Biactive (360g/L glyphosate) at the rate of 10 ml to 1 litre of fresh water
- Hand weeding
- Control: do nothing
The experiment was initiated in 2013 following autumn and spring burns. Experimental "blocks" are 1 m x 1 m, and contain 4 experimental plots of 250 mm x 250 mm. The plots are randomised within the blocks. We allocated 11 blocks to experimental area B, 12 to experimental area C and 6 to experimental area D. Experimental area D is in the spring burn, while three of the blocks have been caged. See below for a map of the experimental area.
Experimental plots are divided into 25 50 mm x 50 mm units. Monitoring involves recording presence or absence of three weed categories: grass, Lotus spp., or flat weed. Monitoring was initially done 6 monthly and more recently yearly. In 2015, we also recorded all species present in each plot. This revealed that spraying, in particular, caused little damage to the native species, a very comforting result.
Monitoring in 2015-16 was delayed until mid-summer to minimise the presence of newly germinated seedlings, as recommended following the previous monitoring. However, with drought conditions in spring and early summer 2015, conditions were very dry at the time of monitoring and some of the (perennial) weedy grass had dried off. It was sometimes difficult to determine whether the grass was dead or simply deciduous leaving live rootstock.
The percentage reduction in focal weed occurrence across all four treatments continues to converge. This may be partly due to the dry conditions described above. The Control treatment is still the weediest, with Hand weeding and Spraying still showing benefit from the initial treatment. Although not shown in the chart above, the spring burn units have a similar pattern of results.