Lawn Grubs

Grub out Lawn Grubs

Archive for October, 2011

Australian Lawn Grubs 3 – African Black Beetles


 

African Black Beetles, Heteronychus Arator, are believed to have originated in Southern Africa. The presence of african black beetles in Australia was first recorded in New South Wales in 1920s. 

Usually found in Australia, african black beetles are also called black lawn beetles because they feed on lawns and grasses. African black beetles are considered as pests for non-legume crops and plants in Western Australia, Eastern Australia, Victoria and Southeast Queensland. There have been reports of attack in grapevines in McLaren and Adelaide Hills in South Australia. 

African black beetles cause significant economic damage to roots of different horticultural crops such as young rooted vines, newly-planted cuttings, olives, potato crops, and other vegetables. African black beetles also attack lawns, newly-sown pastures, young trees, and thin wooded plants. 


Life Cycle 

During spring, adult african black beetles become more active as they feed on stems and plants and lay eggs. Female african black beetles lay their eggs during spring up until the early summer. They wait for three to six weeks for the eggs to hatch into grubs. Grubs are typically white curl, C-shaped and grow up to 25 mm long. African black beetle larvae feed on organic materials and plant roots from late summer until they turn into pupae. Hence, new adults appear from mid-summer to early autumn. 

The adult african black beetle has brown to shiny black color. Its elongated, cylindrical body measures approximately 12 mm long and 5 mm wide. The rear legs are larger than the front legs. The rigid head has large, rounded and compound eyes. Usually found on the land surface or below it, adult african black beetles look like cockchafers that move slowly but have the ability to fly. Flight activities also occur during spring, although there are fewer beetles who get involved. 


Symptoms of Infestation 

The destruction caused by african black beetles normally occurs from mid-summer through winter, to early summer of the next season. New generations of adults emerge during the summer season. They feed on the trunks of young vines on the ground level or just below it. As they continue to attack, they cause wilting and collapse of the vine. Although beetle activity may be low during winter, african black beetles continue to ingest and damage the vines. 

A good indicator that african black beetles are feeding on the vine is the presence of splayed fibrous tissue on its stem. There may not be any signs of beetle feeding that can be seen above the ground until damage has progressed. Vines that have been affected by beetle feeding commonly turn red or yellow. 

Similarly, there could be african black beetles present when the grass dies in patches without any apparent reason. The root system of the lawn gets damaged and the grass looks brown or discolored. Additionally, there may also be the evidence of holes and small mounds of excavated soil due to tunnelling activities of african black beetles. 


Management and Control 

Control of african black beetles is generally difficult. October is normally the critical month for lawns. This is the season when infestation of grubs begins and female beetles start to hatch their eggs. 

Insecticides are often ineffective because adult beetles and their larvae spend much of their time under the ground. However, sprays based on chlorpyriphos or imidacloprid have been found to be an effective means of controlling african black beetles.  

Research has shown that african black beetles survive and reproduce in grassy areas, like ryegrass and paspalum. Therefore, cultivation of soil before planting as well as crop and pasture rotations help reduce the damaging effects of african black beetles. Furthermore, laying plastic mulch over elevated vine rows may control the beetles from crawling to the base of the vines.