Gippsland - How Now Gippy Now - April 2010 Edition
Will we have cockchafers this year?
Despite the very wet spell much of Gippsland experienced last September, many farms may suffer cockchafer damage again this autumn.
A long wet autumn/winter is probably the only way that cockchafer numbers will be reduced to those of the late nineties.
When the true autumn break finally arrives, don’t wait for too much pasture to start disappearing before looking for signs of cockchafer activity. Start looking for signs of whether you have a black or redheaded cockchafer problem - hopefully not both.
Following are very brief descriptions of their life cycle and it may help you understand what occurs and when you must carry out any possible control actions as recommended.
Blackheaded Cockchafers
Remember the hundreds of thousands of narrow brown-black beetles of 10 to 11 mm length being attracted to your house, dairyshed or headlights in late January-early February? These are the adult beetles of the black‑headed cockchafer emerging from the ground, and the females flying to lay their eggs about 100 mm into the soil, generally into very short pastures.
These eggs hatch within two to three weeks and survive on the humus in the soil until the autumn break. After autumn break, the young blackheaded cockchafer grubs (larvae) tunnel to the surface in the rain-softened soil. The grubs have dark brown to black heads and white or greyish-white bodies and curl into a “C” shape if disturbed. Their bodies become more creamy yellow in mid-late winter as they fatten, readying themselves for pupation during spring and summer before emerging for their next cycle as beetles.
They come to the surface at night only and particularly after a rain event or heavy dew. They chew off grass leaves and drag them back down their tunnel for later feeding. They remain in these tunnels during the day.
Signs of Blackheaded cockchafers: Ryegrass disappears from pastures leaving bare patches where weeds grow such as capeweed, flatweed, plantain. By this time, small mounds of dirt can be more easily seen around their tunnel entrances.
To check for cockchafers, use a shovel in the unaffected pastures near the damaged areas to spade head depth. If two or more black headed cockchafer grubs per shovelful of soil are frequently found then consider spraying the blackhead. Avoid waiting too long before action.
Control: Blackheaded cockchafers can be effectively controlled using registered insecticides applied to the green pastures they are feeding on. Treat if about 80 grubs per square metre or more are found. Apply the chemical before a rain fall or heavy dew is to occur, but you must allow enough time for the chemical to dry on the plants. Failing this, spray soon after rain, but try to ensure the chemical does not run off the leaves.
Redheaded Cockchafers
These beetles tend to fly at dusk between August to October and are not so noticeable when they are on the move. The adult redheaded cockchafer beetle is squat and dark brownish-black in colour and the grub body is very similar to that of the blackheaded grubs, but their heads are red or orange coloured.
The redheaded cockchafer has a two year life cycle. They remain underground and chomp on the living and dead plant roots and other humus approximately 2 to 4 cm below the ground surface, hence never coming to the surface to feed.
Signs of Redheaded cockchafers: Dead pasture, more so than bare ground, will be noticed amongst the remaining green plants in the early stages. However, the digging action of flocks of large birds such as ibis and crows will leave the ground surface in a very disturbed state. After a prolonged dry spell, it can be possible to roll up the affected pasture like a carpet in severely damaged pastures.
Redheaded cockchafer grub
However, if heavy rains occur this autumn, the redheaded cockchafer damage may not be so obvious because the “cockchafer pruned” roots can often survive due to the continual supply of rain.
Control: Control is very difficult since these grubs never come to the surface to feed. There are no registered chemicals available for control of this particular cockchafer grub in a pasture situation.
If large areas of pasture are lost due to the Redheaded cockchafer, anecdotal farmer experience has been that resowing by direct drilling has usually been an expensive lost cause, unless done in the winter when the soil is cold and grub activity has decreased substantially. Then, pasture growth will be very slow till spring.
Many farmers have experienced greater success by power harrowing or chip hoeing the top few centimetres of soil. This activity physically damages many of the grubs and brings many to the surface for easier pickings for the birds, but the grubs below the disturbed level will not be affected. The disadvantage of this action is that the paddock surface will be soft and grazing now into the winter will be difficult.
NOTE: Some desperate landowners have tried several off-label or unlawful methods in attempts to control the red heads, but such practices can render the person carrying out the chemical spraying liable to legal action. Applying off-label rates and unregistered chemicals at two to three times the amount of water normally recommended can result in the dilution of the active ingredient and the effect of clay colloids or organic matter on the chemical efficacy will reduce its effectiveness. This approach or doubling the chemical application rate is also likely damage or kill many of the beneficial soil organisms.
More information is available in the DPI Information Notes Series on the DPI website, www.dpi.vic.gov.au, and search for cockchafers. For information on suitable chemicals to control the blackheaded cockchafers, please consult your local chemical retailer.
