In susceptible regions of WA - primarily the higher rainfall areas adjacent to the south-west and southern coasts - consider monitoring for African black beetle adults prior to planting.
Adult flight activity can be monitored during summer or autumn by using light traps, or observing activity around lights near buildings and street lights. High levels of flight activity indicate the possibility of crop invasion.
Adult beetles occur no deeper than 15cm in soil, and are usually just below the soil surface.
Spade sampling across a paddock can be used to gauge their abundance. This can be estimated by considering that 44 x 15cm square spade samples = 1 square metre. More than three adult beetles per square metre is considered a threat to susceptible crops.
Because beetles are clumsy walkers, they accumulate in pitfall traps or sharp-sided plough lines. A simple pitfall trap can be made using an aluminium can with the top removed, or a glass jar buried in soil to ground level.
Sentinel drenching with an insecticide toxic to adults can also be used to assess presence - Refer to Viticulture spray guide for Western Australia or consult the Australian Pesticides and Veterinary Medicines Authority portal.
Sprays can be applied to marked areas before planting, or the base of tagged grapevines across a block after planting. The resulting dead beetles should be counted within two days of spraying. Remedial action should be considered if there are more than three to six beetles per square metre in a paddock, or 5% or more of grapevines with beetles. Sentinel drenching may be repeated at selected times of the year or after a suspected fly-in.
African black beetle is difficult to control as the soil acts as a protective blanket, and makes it difficult to judge pest abundance.
If beetles exceed the thresholds suggested above, consider the following control techniques.
For current information on registered insecticides, consult the Viticulture spray guide for Western Australia or the Australian Pesticides and Veterinary Medicines Authority portal.
Resident populations of African black beetle can be reduced by applying insecticide to the soil surface in late winter, when the crawling activity of the insect increases. This may have the added benefit of controlling the insect before egg laying commences in spring, helping to reduce numbers of beetles in the area for a longer period. However, the possibility of fly-ins also needs to be considered.
When transplanting grapevines, a slow-release insecticide-incorporated polymer granule can be applied around the base of the young vines. The granules need to be covered by soil to protect them from environmental degradation.
If applied correctly and vines are managed well, granules should be active for two years. By this time the vines are large enough to no longer be susceptible to stem girdling by the beetles.
Should control of an infestation of beetles be required after transplanting vines, this can be achieved by drenching around the base of vines with an insecticide solution. The same technique can be used to monitor for the need to retreat as described above.
For detail on insecticide use in WA vineyards, consult the sources listed above.
Some of these methods may also be relevant for similar pests in other crops, provided that the insecticide is registered.
To control African black beetle prior to planting potatoes, incorporate insecticide to a depth of 15cm. Use a rotary hoe to ensure thorough mixing, as this maximises direct contact of the insecticide with the beetles. Relying on beetles to crawl through treated soil is less effective. Use the higher registered rates for heavy infestations as it is particularly effective in reducing stem damage, which can kill plants.
Also consider applying insecticide prior to a light rain event, as the insecticide will be less likely to be lost quickly through volatilisation and cotrol adult beetles walking on the soil surface at night. This is most relevant to controlling fly-in infestations late in a crop cycle.
The insectcide applied may not persist in soil more than one week after application at a dose sufficient to kill newly arriving beetles. Therefore pre-plant applications are not effective against beetle infestations later in the life of a crop. In high-risk situations, monior after an application and from those observations, decide whether a follow-up application is required.
Systemic insecticide seed dressings applied to protect newly planted crops have been effective in field trials against adult beetles.
Having established the risk of damage by African black beetle, the area to be planted should be kept as bare fallow for as long as is feasible. However, susceptibility to wind and water erosion also need to be considered.
Because kikuyu is a favoured food plant that can sustain high beetle populations, consider removing it as early as possible prior to planting. Plants considered less favourable to ABB include oats, and some broadleaved plants such as lupins.
Larvae are susceptible to the entomopathogenic nematode Heterorhabditis bacteriophora, which occurs naturally in eastern Australia. Nematodes live in the soil and spend their lives attacking the larvae and/or pupae of African black beetle and other soil-dwelling insects. They develop on or within the insect. While nematodes are a relatively expensive option, they are suitable for high value crops such as amenity turf. For maximum effectiveness, soil temperature should be above 15°C with high soil moisture levels and the nematodes should be applied when larvar are at least half way through their development cycle. Nematodes track their host using a gradient of carbon dioxide and the larger the larva the more easily the nemtode will locate it. Also, largar larvae have large entry points such as spiracles - the breathing pores of insects.
Birds such as guinea fowl, chickens and ducks are used increasingly to control of a range of pests including adult beetles, wingless grasshoppers, garden weevil and snails.
Beetles exposed in the process of land preparation or by a winged ripper to expose soil and beetles, would assist in this form of pest management.
Growguards are used in some crops to protect new plantings from herbicides and rabbits. If the growguards are buried to about 5cm, they can also prevent attack by African black beetle adults.
Another form of physical control has been developed by and for the blue gum industry. This consists of a plastic mesh sleeve placed over the root ball and along most of the stem of treelings.
These sleeves make it impossible for adult beetles to feed on stems of plants at ground level. This technique may be suitable for other crops where planting material is small enough to be placed in the sleeves, such as bare-rooted vine transplants and olive treelings.
Because beetle adults are clumsy walkers, planting into black plastic mulch on slightly raised, angled beds may help reduce the numbers of adult beetles that are able to walk to the base of plants. The plastic also assists with weed control.
If damage to the stem of grapevines near ground level has occurred, mounding soil around the base of affected plants may enable those plants less extensivly damaged to recover. Insecticide treatment may still be required to control the beetles. Mounding may also be applicable for rejuvenating damaged blue gums, olive trees and other plants.