What are Ground Pearl?
The first step to control Ground Pearl is to understand exactly what Ground Pearls are. Ground Pearls have become more of an issue in recent years, and Ground Pearl control and treatment is now a problem in sugar cane, vines, grapes, oil palms and turf grass.
They are scale insects that belong to the Margarodidae family, and get their name as they look like pink pearls. You see Ground Pearls in the soil or thatch as small pearl-shaped balls. The female is pink and has claws and front legs. The male is smaller than the female, and has a slender waxy “tail” that is up to 6mm long.
The “pink pearl” is the nymph which has a hard, globular, yellow to purple shell. The nymphs are up to 1.5 mm in diameter.1Buss EA. (May 2009). Insect Pest Management on Turfgrass. EDIS. (29 November 2012)
This, waxy, spherical shell is what you tend to see in the field. Immature first-instar nymphs and cysts (second instars) are the feeding and growing stages. This is especially the case in sandy soils. Adult males and females lack mouth parts and do not feed. The image below is courtesy of NC State Extension.
What Does Ground Pearl Damage Look Like?
You can see damage in turf from Ground Pearl nymphs as circular patches that look like fairy rings. These are often seen in dry weather as irregular patches of turf, that turn yellow or brown in the Summer. Thet then either die in the Winter or never green up in the Spring. Each year these patches enlarge and the problem gets worse.
Ground Pearl nymphs extract nutrients from plant roots and weaken the host plant. If you suspect you have Ground Pearl check the boundary between the healthy and chlorotic turf. This is where you will see the greatest numbers of Ground Pearl in turf.2Potter, D.A. 1998. Destructive Turfgrass Insects: Biology, Diagnosis, and Control. Ann Arbor Press, Ann Arbor, Mich..
Biology of Ground Pearl.
Over the last decade, Ground Pearl in turf have become more of an issue in Australia. Sports facilities such as bowling greens, golf clubs and sports grounds have all reported instances of the Ground Pearl damage in turf. The roots of couch, buffalograss, and zoysia, are commonly infested with Ground Pearl which are easily to see by their pink pearl appearance.
Lifecycle.
The pink female Ground Pearl tend to mature in the late Spring and then emerge from their cysts. They then tunnel 50 to 75 mm into the soil, where they then secrete a waxy coat. Inside this they lay up to 100 eggs, and under the right conditions a female may lay eggs several times a year. It only takes a few days before the eggs hatch.
The first instars (crawlers) then move and infest roots. Once they do this, the nymphs secrete their outer cover and develop into “pink ground pearls.”
However, if conditions are not favourable, female nymphs may remain in the pearl stage for several years. In fact, Ground pearls have been known to survive for 15 years in the absence of a suitable host3Brandenburg, R. 2003. Don’t give up on ground pearls. Grounds Maintenance. (http://www.grounds-mag.com/mag/grounds_maintenance_dont_give_ground_2)..
During the Summer and into the Autumn the nymphs continue to develop. By the late Autumn or early Winter the insects are adults, and then spend Winter inside the cyst (pearl) that surrounds them. Their life cycle of Ground Pearl in turf appears to be mainly parthenogenic.
This is a form of asexual reproduction where offspring develop from unfertilized eggs, and has several competitive advantages:
- Rapid population growth.
- They do not need a mate to reproduce.
- They can rapid colonise new areas.
In the mid-Summer the slender nymphs emerge, and then infest grass roots. Once they start to feed, the nymphs soon develop their globular appearance which makes Ground Pearl in turf so difficult to manage. There is usually one generation each year.
How do Ground Pearl Move?
From the above image, you can see that Ground Pearl in turf aren’t very mobile. Their small size, and the fact that they live below the surface means that they are unable to move very far under their own power. This is a big issue when it comes to Ground Pearl control.
To get to a new site they must dig through the soil. One estimate is that they only move a maximum of 10 to 15 cm per year4Hoffman E, Smith RL. 1991. Emergence and dispersal of Margarodes meridionalis (Homoptera: Coccoidea) in hybrid bermudagrass. Journal of Economic Entomology 84: 1668- 1671.. This inability to move very far is key to managing Ground Pearl in turf.
Managing Ground Pearl.
There are two ways to manage Ground Pearl in turf, and an integrated program of chemical and cultural control gives the best control of Ground Pearl in turf grass.
Cultural Control.
- Don’t use grass from infected sites if you establish turf with sod or sprigs.
- Clean machinery if you use it in infected areas.
- Ensure that nutrition and water do not limit growth. This gives you a better chance to get turf recovery as fast as possible.
- Use a premium soil wetter such as HydroForce Ultra. If you can get water further down into the soil profile you will produce healthier turf and also get any chemical applications further down into the profile.
To my mind, this first two measures are the most important in a cultural program.
- As Ground Pearl only move 10 to 15 cm a year, if you clean soil from aeration equipment, wheels of equipment and do not use infested vegetative material these will all limit its movement. Turf contractors please take note!
Chemical Treatment of Ground Pearl.
One of the problems with ground pearl control has been the waxy coat on the nymphs. This has meant that Ground Pearls are resistant to insecticides when they are inside these pink pearly cysts.
The focus of Ground Pearl are the adult females and crawlers as these do not have a waxy cover. This is the reason why ProForce Scarlet Trio states on the label to apply it when you detect the adults or crawlers from the early Spring to the end of Summer. This is when Ground Pearl are at their most vulnerable.
Scarlet Trio for Ground Pearl in turf
Research at Clemson University for Ground Pearl found that three months post-treatment, no product had an impact on Ground Pearl populations.
At nine months, products that contain the active ingredients clothianidin (in combination with a soil wetting agent) and thiamethoxam seem to have some efficacy but do not give “great” control. Clothianidin is one of the key ingredients in Scarlet Trio.
One thing to note is that broad-spectrum insecticides had higher cyst numbers and are likely to harm beneficial natural enemies 5https://www.gcmonline.com/course/environment/news/ground-pearls-turf.
Ultimately, if you maintain a healthy, vigorous turf cover you are better able to minimize damage.
Part of this approach is to be careful when you select a pre-emergent herbicide to minimize root damage. Anything that impacts on healthy root growth will make the damage caused by this pest worse. So avoid using pre-emergent herbicides that have the potential to prune roots.
References
Graduated from Newcastle University with an Hons Degree in Soil Science in 1988, Jerry then worked for the Sports Turf Research Institute (STRI) as a turf agronomist before emigrating to Australia in 1993.
He followed this by gaining a Grad Dip in Business Management from UTS. He has worked in a number of management roles for companies as diverse as Samsung Australia, Arthur Yates and Paton Fertilizers.
He has always had a strong affinity with the Australian sports turf industry and as a result he established Gilba Solutions as an independent sports turf consultancy in 1993. Jerry has written over 100 articles and two books on a wide range of topics such as Turf Pesticides and Nutrition which have been published in Australia and overseas.
