Lucerne Seed Industry Biosecurity Code of Practice for Golden Dodder
Knowledge straight out of the USA
By Mark Kester, Executive Committee Member
Golden Dodder is becoming a concern for the lucerne seed industry so this year, I applied for, and was awarded the Hugh Roberts Travel award, with thanks to Rural Industries Research and Development Corporation (RIRDC).
I travelled to the USA and see first-hand how US farmers live with, and control, Golden Dodder. I visited Shannon Mueller, Agronomy Farm Advisor at University of California Cooperative Extension in Fresno County, Bill Knipe at Forage Genetics International, Tom Lanini, a weed scientist at the University of California at Davis, and Jose Arias, a production manager with Forage Genetics in Nampa.
The highlight of my trip was witnessing the harvest of a Forage Genetics International variety winter activity 4 near Nampa, which cleaned out at 2.2 tonne/hectare! Why can’t we achieve that in Australia? What I observed in California and Idaho was perfect conditions with long, sunny days, warm nights, pure water from melted snow, deep soil (10-50 feet deep), perfect harvesting conditions and leafcutter bees spread through crops on trailers. The lucerne stand I viewed was two years-old and originally sown at 570g/hectare in 50cm mounded rows. Then, following the first harvest, half the plants were removed by cross cutting. By comparison, I think we do quite well here in Australia in a normal year.
Golden Dodder is a leafless, parasitic weed which removes nutrients, reduces yield and even kills its host plant. Dodder contamination poses a huge threat to lucerne, pastures and seed crops. In Australia, lucerne seed contaminated with this weed is banned from export, potentially posing a huge threat to our industry.
Golden Dodder is widespread in the USA. It germinates in early summer when soil temperatures are 15-38 degrees, with an optimum temperature of 30. Due to the size of the seed (1-2mm in diameter), emergence is limited to the upper 4cm of soil with peak emergence occurring at 0.5cm soil depth.
Dodder seeds germinate independently from the host plant presence, but won’t survive if they don’t attach themselves to a host plant (which has to be within 6cm) within 5-21 days.
Dodder lives entirely from the sugars, minerals and water parasitically extracted from the host plant as it winds itself around the stems and leaves growing as much as 7cm per day always in a counter clockwise direction covering up to three square metres in a season, capable of setting 10,000 viable seeds in 60 days from germination.
US lucerne farmers need a control method for dodder and the best practice consists cutting the lucerne in early summer and spraying 570kg/hectare of sulphuric acid with specially built “terrigators” which will burn off any germinated Dodder. This does set back the lucerne for a period, but gives a benefit of reducing the soil pH. Trials have achieved yield advantages of 73kg/hectare which in turn pays for applying the acid.
While sulphuric acid is not available in Australia, an option is to apply a high rate e.g. 22.5 kg/hectare of Treflan “TR-10” and watered-in by at least 12.5mm irrigation.
The second choice for controlling Dodder, but not quite as effective is Pendimethalin (Prowl as registered in the USA or Stomp 330 as registered in Australia). Applying high rates of 8-12.5 litres/hectare before any dodder has emerged is recommended. Studies have also found that a year of wheat followed by corn will reduce the number of dodder plants by 90 per cent.
Those I met confirmed that options for the future are breeding resistant varieties (such as with some tomatoes) and Roundup Ready which is now released in the US.
However, the best control method is simply by stopping the spread of Dodder. I was told that the main spread is via harvesters and those I met stressed the importance of cleaning down machinery. In addition, being vigilant to record which properties your contractors have been is critical, and always have confirmation that their machinery has been cleaned.
Finally, if you are thinking “I will never get Golden Dodder on my farm” then think again. In this region of the south-east of SA, I can provide names of at least 12 farmers who once said the same thing and now have the parasitic weed. They have no idea how it came to be in their paddock.