Ground pearl in turf. 33

The first step to control ground pearls is understanding what they are. Ground pearls treatment is becoming more of an issue, as these pink pearls are now an increased 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.

As their name suggests you see ground pearls below the surface as small pearl-shaped balls in the thatch or soil. The female is pink and has claws and front legs. The male is smaller than the female, but has a slender waxy “tail” 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 most likely what you’ll see in the field. Immature first-instar nymphs and cysts (second instars) are the stages when it is actively feeding and growing. This is especially the case in sandy soils. However, adult males and females lack mouth parts and do not feed. The image below is courtesy of NC State Extension.

Ground Pearl Damage.

Damage from Ground pearl nymphs causes circular patches that look like a fairy ring. You often see damage in dry weather as irregular patches of turf. These turn yellow or brown in the Summer, die in the Winter or never green up in the Spring. Each year these patches enlarge and the problem worsens.

Ground Pearls nymphs cause this damage by extracting juices from underground plant parts, and this removal of nutrients from roots weakens the host plants. If you suspect you have Ground Pearl check the boundary between healthy and chlorotic turf. This is where the greatest numbers are usually found and so you are more likely to see them here.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 along the Eastern seaboard of Australia. Sporting venues such as bowling greens, golf clubs and even sports grounds have all reported instances of the damage these cause. The roots of couch, buffalograss, and zoysia, are most commonly infested with ground pearls which can easily be identified by there pink pearl appearance.

Lifecycle of Ground Pearl

The Pink females 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. Within this covering they lay up to 100 eggs, and under the right conditions a female may lay eggs several times a year. After only a few days 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 right to emerge, 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 overwinter in the cyst (pearl) that surrounds them. The life cycle appears to be mainly parthenogenic.

The slender nymphs emerge in the mid-Summer and then infest grass roots. Once they start to feed, nymphs soon develop their globular appearance which makes ground pearl treatment so difficult. There is usually one generation each year.

Movement of ground pearl.

From the above image, you can see that ground pearl 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 feeding 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 a key part of any cultural control program.

Ground Pearls Treatment.

There are two options for ground pearls treatment. These are firstly cultural management, and secondly chemical control with the launch of Scarlet Trio.

Cultural Control.

Currently only Scarlet Trio is registered for this pest. So an integrated program with Scarlet Trio plus cultural control will give the best control of ground pearl in turfgrass.

• Don’t use grass from infected sites if you establish turf with sod or sprigs.
• 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 control measure is the most important but is one that is seldom carried out. If you move between sites clean equipment to minimize the spread of ground pearls. As they 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 Pearls.

One of the problems with successful ground pearl control has been the presence of the waxy coating on the nymphs. This has meant that ground pearls are resistant to insecticides when they are inside these pink pearly cysts as they are protected.

The focus of any chemical treatment of ground pearl must be 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 when the adults or crawlers are detected from the early Spring to the end of Summer. This is when ground pearls are at their most vulnerable.

Research at Clemson University looked at insecticide applications for ground pearl control. This 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 (combined with a 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 (particularly products containing carbaryl) 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 carefully 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 cause prune roots.