Pasture dieback kills summer growing grasses. These grasses are also known as C4, subtropical or tropical grasses. It is a complex condition involving pasture mealybug (Heliococcus summervillei). Pasture dieback begins in patches which can grow to affect large areas, significantly reducing pasture productivity. . The condition has spread rapidly and now affects many sown and some native summer grass species in Queensland and NSW. It has been detected in districts across eastern Australia from Far North Queensland to the North Coast of NSW.
It is important to observe changes in the pasture over a period of time as this helps to differentiate pasture dieback from other disorders. In many cases, early diagnosis combined with professional agronomy services can help landholders develop an effective response. Dieback symptoms are most obvious and progress quickly when grasses are actively growing, especially after significant rainfall.
- Leaf Discolouration
- Stunted and unthrifty plants
- Plant death
- Weeds Invade bare areas
To date only summer grasses have been affected by pasture die back with some being more affected than others.
Grasses vary significantly in their susceptibility to pasture dieback, with the most susceptible including Kikuyu, Bissett creeping bluegrass, and Sabi grass. Less susceptible but still affected include American/Gayndah buffel grass and digit grasses, while Biloela buffel, Signal grass, Narok Setaria, and Mekong Brizantha show higher tolerance.
For pasture dieback to occur it requires only two factors to be present. Those factors are the present pasture grass is a C4 grass and the presence of pasture mealybug.
Increased prevelance and susceptibility generally occur under the following conditions:
High grass biomass, highly susceptible grass and hot and humid conditions.
Decreases prevalence and severity generlly occurs under the following conditions:
Low grass biomass, less susceptible grass, Cool or dry conditions, Grass is not actively growing, Predatory insects present, Legumes present. Regular soil testing in Queensland can assist in monitoring pasture health and identifying contributing environmental factors.
Pasture dieback guide NSW DPI:
https://www.dpi.nsw.gov.au/__data/assets/pdf_file/0009/1333692/PastureDiebackGuide2ndED.pdf
