Department of Primary Industries:
Blackheads In Your Pasture?
"Are large bare areas of pasture appearing in front of your eyes?" asks Frank Mickan, Pasture and Fodder Conservation Specialist, DPI Ellinbank.
By Department of Primary Industries - 2nd April 2003 - Back to News
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"Are large bare areas of pasture appearing in front of your eyes?" asks Frank Mickan, Pasture and Fodder Conservation Specialist, DPI Ellinbank. Then, the culprits are probably black headed cockchafer grubs (actually their larvae) which have become active after our initial autumn rains. Another culprit, although pasture damage may not be so obvious initially, are the red headed cockchafers.
Three tell tale signs of blackheaded cockchafer damage are:
∑ Small mounds of dirt surrounding little tunnels on the ground surface.
∑ Bare areas in recently germinated sub clover and ryegrass.
∑ Freshly moved soil due to birds looking for larvae.
The blackheaded cockchafer grub is creamy grey in colour with a black head. Other cockchafer grubs have similar body colouring but will have yellow or red heads. The grub lives in the soil in this form until the early autumn rains soften the ground and encourages pasture growth. Over autumn and early winter they grow through three life stages or instars, and continue to consume pasture. Towards the end of the third stage their bodies become a creamier colour. They tunnel about 150 millimetres into the ground. The beetles, which are brown Ė black, emerge and fly in January-February and can fly long distances in summer to lay their eggs. These are the beetles you will have noticed flying into your windows when the lights were on.
The grub comes to the surface, in response to rains and heavy dews, to feed on the pasture overnight. They then munch on it in their tunnels throughout the day.
To check for cockchafers, dig into the soil in the unaffected pastures near where areas have become bare. If two or more grubs per spadeful of soil is regularly found, then spraying is recommended - particularly if large areas of pastures are being bared out. Dig over several positions and paddocks. Donít wait for large areas of dead pasture to show up before instigating control methods.
Several chemicals are registered for the control of the blackheaded cockchafer grub and have varying withholding periods. Contact your local chemical supplier and please read the entire label since many changes have occurred over recent years concerning the instructions and warnings of various chemicals. There may be legal implications for you to consider.
The ideal time to spray is just prior to rain or dew is expected, but the pasture must have enough time to dry out to prevent the spray being washed off the plants. Predicting the next shower can be difficult so the next best option is to spray soon after rain, once again, making sure the chemical does not run off the foliage. Applying chemicals in July/August will be too late because they will be further advanced in their lifecycle, and will have stopped feeding.
Large areas of bared out pasture may need oversowing once the grubs have been controlled. Alternatively, these areas may need to be oversown in spring, or the following autumn, to prevent flatweed, capeweed etc from claiming the bare ground.
SPREAD FERTILISERS NOW!
Phosphorus fertilisers have traditionally been spread in Gippsland in the autumn, as the heavy spreading trucks donít damage dry paddocks at this time of year. Applying nutrients in autumn will also maximise autumn and winter growth when feed is at a premium.
Research indicates that there is little if any loss in pasture production if phosphorus fertilisers are applied once a year compared to multiple applications. This is because most of the phosphorus present in soil is tightly held and is not readily lost between once-yearly applications.
Recent research shows that annual phosphorus fertiliser application in the autumn is preferable from an environmental perspective as well. This is because the phosphorus in the fertiliser granules is carried into the relatively dry soil by morning dews and autumn rains, to be taken up and used by the growing pasture. This leaching mechanism is so effective that a couple of weeks exposure to the weather leaves virtually no phosphorus in the granules.
On irrigated farms, autumn is also an excellent time to apply phosphorus fertilisers as the irrigation interval is long and it is easier to apply fertiliser to relatively dry paddocks. After allowing time for the nutrients to leach into the soil, the next irrigation can then be carried out without risking major phosphorus losses.
Spreading fertilisers in the winter and spring on any farm is riskier as the soil is more likely to be wet and any heavy rainfall will inevitably take the fertiliser off the farm and into creeks and rivers, causing a loss to the farmer and the environment.
TUNNEL EROSION - THE SLEEPING GIANT
UNDER YOUR FEET
A small but enthusiastic group of landholders gathered at Glenaladale last week to discuss tunnel erosion.
Julianne Sargant and Peter Robinson, Catchment Management Officers from the DPI Calvert Street office, explained to the group that tunnel erosion is thought to be responsible for large losses of soil and nutrients from farms which reduces productivity and leads to increased sediment input into streams, dams and the lakes. In East Gippsland, people only become aware of tunnel erosion on their property when it becomes a serious problem. The earlier a landholder recognises that they have a tunnel erosion problem, the easier and cheaper it is to fix.
Julianne and Peter are involved in a project to investigate the sediment and nutrient contributions of tunnel erosion to the Gippsland lakes. One aim of the project was to identify the size and severity of erosion in the Mitchell, Nicholson and lower Tambo River catchments, as the numbers of hectares affected by tunnel erosion in these areas is unknown. Landholders in the area were surveyed to gauge an idea of the problem. 130 landholders responded to the survey. Site inspections and evaluations are now taking place on these properties.
The project is also investigating the type and amounts of nutrients attached to sediment entering the Gippsland Lakes. The silt from tunnel erosion is very fine and does not settle, it travels in suspension to the lakes. It is unknown how much nitrogen and phosphorus hangs onto the fine silt particles entering the lakes.
Tunnel erosion forms when sub-surface soil is removed by water. Cracks allow moisture into the soil profile and this surface and subsurface moisture forms tunnels.
Digging out one tunnel wonít solve the problem, the water just moves to the next weakest point. Physical barriers put into the tunnel does not stop the erosion, the tunnel just moves around the barrier.
Mr Robinson explained that his aim was to work with landholders to treat tunnel erosion so that soil was keep on the property and productivity maintained.
"Landholders with tunnel erosion are loosing paddocks, their properties are loosing value. Treating tunnel erosion needs to be affordable. Large machinery is needed, at least D7ís or 8ís. They are more expensive but they are also more effective as they rip to a depth of 3-4 feet. We can solve the problem and increase productivity."
The group then moved to a trial site at Glenaladale, where a conservative estimate of 170 cubic meters per hectare of soil has been lost through tunnel erosion. This paddock has been divided into 6 plots with each plot receiving different ripping patterns and various combinations of lime and gypsum treatments. After the autumn break, the trial sites will be direct drilled with suitable pasture species.
For more information on tunnel erosion contact Julianne Sargant at DPI Calvert Street on
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