The dilemma of Guinea grass (Megathyrsus maximus): A valued pasture grass and an emergent invasive species

Authors: RHODES, AARON - University Of Texas At Austin; PLOWES, ROBERT - University Of Texas At Austin; Goolsby, John; Gaskin, John; CALATAYUD, PAUL-ANDRE - International Rice Research Institute; MARTINS, DINO - Mpala Research Centre And Wildlife Foundation; RUTLEDGE, JIMMY - Farmer; GRAHMANN, ERIC - Farmer; GILBERT, LAWRENCE - University Of Texas At Austin

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/15/2021
Publication Date: 8/4/2021
Citation: Rhodes, A.C., Plowes, R.M., Goolsby, J., Gaskin, J.F., Calatayud, P., Martins, D.J., Rutledge, J., Grahmann, E.D., Gilbert, L.E. 2021. The dilemma of Guinea grass (Megathyrsus maximus): A valued pasture grass and an emergent invasive species. Biological Invasions. 23:3653–3669. https://doi.org/10.1007/s10530-021-02607-3.
DOI: https://doi.org/10.1007/s10530-021-02607-3

Interpretive Summary: Guineagrass, Megathyrsus maximus (=Panicum maximum) is an African grass that is in many parts of the World, including south Texas. Although it has some value as a pasture grass, it also causes many problems including: enhances the survival of cattle fever ticks, Rhipicephalus microplus and Rhipicephalus annulatus along the U.S.-Mexico transboundary region; invades subtropical perennial crops such as sugarcane and citrus, reduces populations of granivourous birds such as quail; and alters fire regimes in South Texas rangelands. South Texas rangelands have been invaded by a unique small form of Guineagrass that is genetically distinct from other Guineagrass populations worldwide. This small form of Guineagrass has been matched with populations near Durban, South Africa. Specialist arthropod candidate biological control agents from Durban are under evaluation to determine if they are specific (feed and develop) only on the small form of Guineagrass and therefore suitable for use in South Texas where this grass is invasive.

Technical Abstract: At a global scale, invasive grasses threaten biodiversity, and ecosystem function. Yet, the movement of grass species is a major economic force driven by globalization. Pastureland and rangeland are of critical economic and ecological importance, but there may be a price to pay when introducing novel grass species. Recognizing that economically important species can also be ecologically damaging creates a contentious debate for land managers, policy makers and ecologists alike. Many Old World perennial grasses have been distributed pantropically given their high forage production and resistance to stress. However, these very traits may also confer competitive ability, increasing the possibility of unintended escape and invasion. Use of classic biological control may alleviate the ecological impact in invaded areas. In this literature synthesis and case study, we examine Guinea grass (Megathyrsus maximus); whose economic value in many countries is undeniable, yet its impact on native ecosystems is a mounting concern. First, we introduce Guinea grass taxonomy, general biology and ecology and the geographic and genetic origins. Second, we review the economic value and the ecological impacts. Third, we review the control of Guinea grass in undesired areas using chemical and mechanical means. Finally, we review current efforts to use biological controls on an undesired short form in Texas. The study evaluates the geographic origins of the Texas invasive short form in its African home range with the hopes that a biological control maybe found for the invasive short form and not the economically important tall form.