There is white stuff in your lawn. At first glance it may look like undissolved, light-coloured fertiliser granules when you part the grass. A closer look shows that small white or yellow sacs, the texture of felt, are attached to the grass stems. When squashed, these ooze a red goo.
You have a lawn pest known as felted coccid in Australia or Rhodes grass mealybug in the US. Although not a scale, it is also called by the common name of Rhodes grass scale.
|Pest characteristics||Felted coccid (Antonina graminis) is a mealybug found near the crown, under leaf sheaths and at the nodes of the lower stems of many grasses. The readily visible stages are waxy sacs that cover the bodies of late juvenile and adult forms. The adults are inside the sac and have a dark brown to purplish sack-like body 1.5-3.0 mm long. They have no legs. The sac itself has a felty or cottony texture and is used by adult females to hold eggs.
The insects are all female. Reproduction occurs without fertilisation. The females deposit 300-600 eggs into the ovisac (egg sac) and one to three weeks later a mobile ´crawler´ stage emerges. Crawlers are flat, with oval-shaped cream-coloured bodies and a pair of long tail filaments. They are 0.8 mm long and are best seen under 10X magnification.
The crawlers seek out a suitable spot, insert their mouthparts into the grass and remain attached to that spot for the remainder of their lives. They feed year-round through three moulting (developmental) stages, sucking sap from the grass and excreting it as honeydew through an anal filament that protrudes through the cottony sac.
In favourable conditions, it takes 60-70 days for an egg to develop into an egg-laying adult. There may be several generations in a season and warm dry weather favours the pest. The lifecycle takes longer to complete through winter. Temperatures over 38ºC slow the lifecycle and can kill some of the population.
|Symptoms||The small white cottony individuals and massed groups are readily visible. Affected grasses turn slowly brown. Death is uncommon in all but the most severe infestations; and when it does occur it is mostly in grasses already under stress. If you have one or more mealybugs per square centimetre of lawn, the infestation is severe.
Lesser infestations cause yellowing, wilting, stunting and thinning of lawns. This may initially be confused with drought stress. As felted coccid secrets a sugary ´honeydew´, the problem can be associated with increased ant and bee activity and with sooty mould.
|Distribution||Of Asian origin, Antonina graminis is also widespread in the Middle East, Africa, the Pacific, southern United States of America and Central America. It is established in all Australian states and territories except for Victoria and Tasmania, where the cold winters break the lifecycle. Exposure to -2°C for more than a day kills the population.|
|Host range||Over 70 species of grass are attacked by Antonina graminis. Lawns of green couch (Cynodon dactylon), Queensland blue couch (Digitaria didactyla) and buffalo grass (Stenotaphrum secundatum) are preferred hosts. Adjacent weed species such as red Natal grass (Melinis repens), Johnson grass (Sorghum halepense) and Rhodes grass (Chloris gayana) may harbour the pest.|
|Control||Felted coccid is readily spread by animals, on grass clippings, through mowing and on infested introduced grass. The crawler stage is dispersed in wind currents. As a consequence, once you have felted coccid, it is a difficult pest to completely eradicate from a lawn. When buying in new grass, check it for the mealybug (and other pests or diseases) on delivery.
There are no registered chemical controls in Australia for the pest. In the United States, chemical control is directed at the crawler stage, prior to the development of the waxy sac that protects the insect from the effects of insecticides. Registered chemicals for the control of associated ant species in lawns (such as the synthetic pyrethroid ´bifenthrin´), may have an incidental impact on the crawler stage.
It is thought that aggressive ants (including Fire Ant, Solenopsis invicta), may protect the felted coccid from natural predators (parasitoids). Baiting measures that kill aggressive ants without affecting the parasitoids, may also assist.
Cultural controls, although not producing a big impact, help to tip the balance back in favour of the lawn. Wear and drought will intensify the impact of felted coccid damage. Any measures to improve plant vigour, such as restricting traffic to encourage regrowth, improving soil moisture and/or nutrient levels, or raising the cutting height assist in reducing the extent of moderate damage.
Other measures that can be taken include:
Do not mow too low, as this can exacerbate the problem. Although cutting high may assist in improving grass vigour during drought, on the downside high-cut but water-stressed green couch appears more susceptible to infestations.
Felted coccid infestations tend to be cyclical. Natural predators such as parasitic wasps and lady beetles will attack the pest and the population normally drops off to non-detrimental levels in time. To encourage parasitoids, refrain from using blanket insecticide treatments and let the problem resolve itself naturally.