If present as the crop matures, adult beetles or whitegrub larvae will feed on tubers making them unmarketable.
If present when brassica seedlings are transplanted, adults of whitegrubs such as African black beetle can chew the stems near ground level killing the young plant.
Management
Check the soil for whitegrubs during cultivation. Avoid sites which have more than one to three larvae or adults per square metre because these soil-inhabiting insects are very difficult to control. If possible, choose another paddock to plant the crop.
Try to rear whitegrubs found in an insect zoo to the adult beetle stage so the species can be identified. To rear larvae, place in a jar with a gauze cover and moist soil with organic mulch and a potato tuber.
If about 5% of brassica transplants or stems of potato plants are damaged by whitegrub adults, apply a contact insecticide directed to the base of plants.
If there is more than 5% damage to potato tubers, harvest as soon as possible.
Acknowledgment
Funding for this work to support Indonesian potato farmers and WA seed potato exports was provided by ACIAR (the Australian Centre for International Agricultural Research) and the Department of Primary Industries and Regional Development, Western Australia.