Watch out for summer weeds
Summer weeds are now emerging across the Central West. These weeds can have a number of impacts on farming systems. These include using valuable moisture over summer, but in addition they can be problematic in grazing systems.
Many of the common summer weeds that grow throughout the Central West such as catheads or caltrop (Tribulus terrestris), common and blue heliotrope (Heliotropium spp.) and many of the panic grasses (Panicum spp.) can be toxic to livestock.
Catheads can cause staggers and secondary photosensitisation due to acute liver toxicity in livestock.
Heliotrope can cause liver damage due to the presence of pyrrolizidine alkaloids. Some panic grasses can also be toxic to the liver and result in secondary photosensitisation with sick and dying stock.
Another perennial weed to be on the lookout for is quena (Solanum esuriale). It has been linked to a condition known as ‘humpy back’ in merino sheep exposed to it over the summer months.
These species mature rapidly following emergence and may start to produce seed within 3-4 weeks of germination. A number of germinations can occur over the summer period in response to rainfall events and so the seedbank of these problematic weeds can increase very rapidly.
Summer germinating weeds are generally highly opportunistic and will germinate most freely where there is little competition and/or ground cover. Therefore encouraging pasture growth over late spring and the formation a mat of residue on the soil surface can assist in reducing emergence.
Chemical application can be very useful in controlling dense infestations, however timing is critical as maturity of the plant is so rapid and repeated applications may be required to control successive germinations.