An Invasive Pest Capable of Destroying Pastures: The Pasture Mealybug Continues to Spread

The pasture mealybug, which has begun to appear on pastures in the US, is attracting attention as an invasive pest capable of causing significant crop losses in grasslands. First identified in Australia, the insect continues to spread across the US. Detected last summer in Texas and Louisiana, the pasture mealybug has also been sighted this year in Florida and Georgia. The pest’s potential for spread and its impact on pasture plants underscore the importance of early detection for producers.

An assessment carried out by Oklahoma State University Extension indicates that the pasture mealybug could cause significant damage, particularly in pasture areas. Dr Ashleigh Faris, Integrated Pest Management (IPM) coordinator at Oklahoma State University Extension and an expert in field systems entomology, who led the research, emphasises the importance of producers recognising the pest and closely examining any unusual damage to pasture.

The pasture mealybug is a very small insect. Adult females reach a length of approximately 2 to 5 millimetres, whilst both females and nymphs have an oval body shape. These insects, which have fine hairs around their bodies, are also covered in a white, powdery waxy coating. This waxy coating stands out as one of the most easily recognisable signs of the pest’s presence. Older, mated females may take on a distinct pink colour. Winged males, however, are rarely seen.

The pest’s impact on pasture plants can have far more serious consequences than its appearance might suggest. As the pasture mealybug feeds on plants, it secretes a toxic saliva. This secretion causes the grass to weaken and become more susceptible to secondary fungal infections. Severe infestation can develop into a serious condition known as ‘pasture dieback’, which can lead to the death of plants across large areas of the pasture.

The first signs of an infestation usually appear as discolouration of the leaves. The process, which begins with the leaves turning yellow, may subsequently progress to reddening and the formation of extensive brown patches. However, as these symptoms can be confused with drought stress, nutrient deficiency or plant diseases, it is important to diagnose the pest correctly.

According to Faris’s assessment, when investigating the pasture mealybug, one should focus on the edges of dead patches in the pasture rather than their centres. The pest is expected to be actively feeding in these areas. It is recommended that lower leaves, sections close to the ground, plant debris and the root collar be examined carefully. In areas where hay has recently been cut, the remaining stubble must be checked.

The small size of the pasture mealybug provides a significant advantage in terms of its spread. As the pest can be carried by the wind, it has the potential to reach new areas. For this reason, it is recommended that farmers carry out regular monitoring in suspected pasture areas and implement biosecurity measures to prevent the pest from being transported to other regions. Cleaning equipment such as footwear, clothing, tractors and lorries used in infested areas is among the practices that can reduce the risk of the pest being transported.

However, there are significant limitations to control measures. It is noted that Sefina Inscalis is the only chemical product labelled for use against the pasture mealybug in Oklahoma. However, it is stated that whilst the product suppresses the pest in low populations and where pasture damage is limited, it is not recommended for use in high-density infestations. It is reported that common pasture insecticides, such as pyrethroids, organophosphates and carbamates, are not effective against the pasture mealybug.

If a suspected infestation is detected, samples must be taken for accurate diagnosis. It is recommended that grass samples be wrapped in dry paper towels, stored in a sealable plastic bag and sent to specialist laboratories. It is reported that Oklahoma State University’s College of Agriculture and the Oklahoma Department of Agriculture, Food and Forestry are conducting a study to form a team of experts to investigate various aspects of the pest and to inform the public.

The spread of the pasture mealybug demonstrates just how serious the consequences can be for pasture ecosystems caused by a small, invasive insect. In addition to causing direct damage to plants, the fact that the symptoms it produces can be mistaken for drought or disease makes control even more difficult. For this reason, regular field inspections, early diagnosis, proper sampling and equipment cleaning stand out as key measures in limiting the economic and agricultural losses that the pest can cause.