Ground Pearl Control in Your Lawn

Ground Pearls are unusual and well-hidden insects. They spend most of their life cycle underground protected in a hard-skinned cyst. The second instar nymph stage – the cyst stage – is the one that causes damage, by sucking sap with its straw-like proboscis.

If you suspect a bare patch in your lawn may be caused by Ground Pearls, the best thing to do is dig down to see if it is them or something else such as Scarab Grubs. Most Ground Pearls should be found between 25 cm and 50 cm underground. Remove any adult females and cysts you find and returf the damaged area. The new turf will have plenty of time to establish because Ground Pearl infestations expand very slowly.

There are no pesticides registered for the control of Ground Pearls in home gardens, so the best thing to do is prevent infestations from spreading as much as possible. Evidence suggests that keeping a well-maintained lawn is your best defence against Ground Pearl damage. Healthy lawns can tolerate an infestation of Ground Pearls without showing any damage or symptoms. Regular applications of organic-based lawn fertiliser, such as Yates Dynamic Lifter Concentrated Lawn Food, will promote healthy lawn growth and make it more resilient to lawn pests and diseases.

Ground Pearls are members of the family Margarodidae and are closely related to Scale Insects. Known pest species that occur in Australia include the Pink Ground Pearl (Eumargarodes laingi), and the White Ground Pearl (Margarodes australis).

Ground Pearls are known to be quite widespread in Queensland and northern New South Wales. In Western Australia they have only been recorded in lawns in the Perth metropolitan area, and some other areas of the south-west.

Male Ground Pearls have not been recorded in Australia, therefore all adult Ground Pearls encountered are female. Adult Pink Ground Pearls are wingless, pinkish, 3 – 5 mm long, 2 – 4 mm wide, globular insects. They look a bit like mealybugs but lack the white powdery coating typical of mealybugs.

Adult Pink Ground Pearls have six legs on the underside of the body, with muscular front legs modified for digging. Adult White Ground Pearl females are similar to Pink Ground pearl females but are cream coloured.

Adult Ground Pearls don't feed, and they don't have functional mouthparts. Although related to scale insects, adult Ground Pearls don't secrete scale covers typical of more familiar scale insect pests such as Red Scale on citrus.

First instar Ground Pearl nymphs are tiny insects about 0.2 mm long known as 'crawlers'.

Second instar nymphs are spherical metallic cysts 1 – 4 mm in diameter. Nymphs are sessile (i.e., don't move) and remain attached to plant roots by the straw-like proboscis they use for feeding. The outer surface of the cyst is known as a 'test', which is a hardened skin that varies in colour from yellowish to bronze/brownish as the cyst ages.

Adult females emerge from their cysts during spring and summer and move about 10 cm away. Adult Ground Pearls are sometimes seen on the surface during summer on hot mornings. The females then lay eggs into a wax-lined chamber about 25 cm underground – up to about 100 eggs for White Ground Pearls, and up to 600 eggs for Pink Ground Pearl.  The females die after laying all their eggs, which hatch into first instar nymphs 1 – 2 weeks later.

First instar nymphs ('crawlers') spread out from the egg chamber to seek a root to feed on and then moult to the second instar cyst ('pearl') stage. Initially, the cyst is about the size of a grain of sand but over time it increases in size to about 4 mm in diameter. To grow in size the 'test' of the cyst splits, the nymph expands, and then a new 'test' forms.  Ground Pearls spend most of their life as cysts – anything from 2 to 5 years, depending on the species and the conditions involved.

Ground Pearls are pests of Sugarcane and grasses including Couch grass (Cynodon dactylon), hybrid Couch grass ( dactylon × C. transvaalensis), Queensland Blue Couch (Digitaria didactyla) and Kikuyu (Pennisetum clandestinum).

Ground Pearl damage can be seen as circular patches of wilting grass (similar in appearance to drought stress); slowly growing bare patches spreading about 10 cm per year, and weeds infesting bare patches.

Look for slowly forming and slowly expanding bare patches. And, look for slowly moving adult Ground Pearls on the surface during hot mornings.

Make sure any new turf delivered is pest free.

Keep your lawn as healthy as possible by watering and feeding appropriately. Evidence suggests that a well-maintained lawn can tolerate an infestation of Ground Pearls without showing any signs of damage.

The natural enemies of Ground Pearls have been poorly studied in Australia. Predatory beetles may feed on them, and fungal diseases may infect them.