Branched broomrapePine oil extract kills the seeds
[Photo: Orobanche ramosa]
Branched broomrape (Orobanche ramosa), is a parasite of broadleafed plants that attacks a wide range of crop plants and weeds. It is an annual plant that germinates only when suitable hosts are growing near it.
The weed contains no chlorophyll and relies entirely on its hosts for its nutrition. It grows underground for several weeks before it emerges, then flowers and sets seed within a few days. The yellow-brown plant quickly produces sweet-smelling, bell-shaped blue to mauve flowers and thousands of minute, dust-like seeds.
Branched broomrape is susceptible to a variety of herbicides, and eradication trials indicate systemic chemicals applied to the host are capable of killing the weed before it emerges. However timing is critical.
Current research indicates a combination of host denial - ensuring there are no crop or weed hosts for the parasite to attach to - and seed decay holds the key to eradication of this dangerous weed.
A herbicide made from extracts of natural pine oil is being used as a soil drench to kill the seeds of branched broomrape. The product, Interceptor™ Concentrate Weed Control, is registered for control of weeds in Australia and NZ, but not in broadacre or horticultural crops.
Last year Interceptor™ was used in two ways: as a soil drench to kill seed in the soil during winter and as a knockdown, to "mop up" emerged plants found by inspectors during the annual spring paddock inspection and to kill seeds on the soil surface around them. Weeds CRC and University of Adelaide researcher John Matthews, whose work is funded by the GRDC, has found that Interceptor™ - at a rate of 1000 litres per hectare in 20,000L/ha of water - will kill broomrape seed in the soil.
The pine oil based product, which is certified organic, may replace methyl bromide for fumigation of branched broomrape infestations once registration issues have been addressed.
Preventing emergence and renewal of the seed bank is a key part of the eradication program, which is focusing on natural destruction of the seed in the soil as the most cost-effective method. This is backed up by eradication of isolated infestations using methyl bromide fumigation where this is identified as being of greatest benefit to the eradication objective.
Methyl bromide is costly, difficult to apply and has significant practical and environmental limitations, but is currently the most effective way of killing broomrape seed in the soil. High rates of Interceptor™ - which is significantly cheaper and has few of the practical and environmental limitations of methyl bromide - appear almost as effective. However, the high water volumes required to carry the Interceptor™ deep enough into the soil to kill seed below the soil surface in non-irrigated farm paddocks is a major logistical challenge. Last season the eradication team trialled helicopter application but were unable to achieve consistent rates across the paddock. This year they will use a 10,000-litre high-volume boomspray for paddock-scale applications of Interceptor™.
The Australian Pesticides and Veterinary Medicines Authority has issued permits for use of Interceptor™ for research purposes this season in cereal paddocks prior to planting, in natural vegetation and pasture, around native vegetation, immediately adjacent to horticultural crops, in crop verges and within broadacre and cereal hay crops.
Region North, South, West