Australia
October 21, 2019
Department of Agriculture and Fisheries (DAF) pathologist Lisa Kelly is encouraging growers to plan early on paddock management, varietal selection and seed sourcing to minimise disease risk in the event of a seasonal break. Photo GRDC.
Northern growers pinning their hopes on a summer mungbean plant are being encouraged to plan early on paddock management, varietal selection and seed sourcing to minimise the risk of costly bacterial and fungal disease infection.
Collaborative research investments by the Grains Research and Development Corporation (GRDC) and the Department of Agriculture and Fisheries (DAF) have enabled scientists to better understand the behaviour of mungbean diseases and equip growers with practical advice on managing their incidence and severity across different seasons and growing environments.
DAF plant pathologist Lisa Kelly said the management practices employed would vary according to the disease but included growers planting seed with the lowest possible levels of infection, selecting varieties with higher levels of resistance, the use of good farm hygiene, effectively controlling weeds and volunteers, and adherence to recommended crop rotations.
“Utilising an integrated disease management strategy is the most effective way to minimise the risk of disease epidemics. Relying on one strategy alone will not be enough to prevent disease,” Ms Kelly said.
“The three aims of integrated disease management are to reduce pathogen inoculum carrying over from one season or paddock to the next, exclusion of the pathogen, and protection of the host.”
Inoculum reduction is reliant on appropriate paddock selection following consideration of previous crops, the history of diseases in the paddock and the presence of other crops and weeds nearby.
Ms Kelly said many pathogens had a wide host range and could infect neighbouring crops and survive in crop debris.
“Avoid planting two consecutive legumes in the same paddock, and rotate mungbeans with other crops for at least three years to help break the pathogen cycle,” she said.
“Soil borne pathogens, such as Fusarium wilt, will survive in the soil for several years and therefore paddocks with a history of soil borne diseases should be avoided.
“At the same time, many pathogens will survive between seasons on volunteer mungbeans and weed hosts. Therefore, vigilance with weed management will help minimise disease transmission
“There may also be a role for the removal of crop debris and stubble management when there is a high risk of inoculum carrying over to the next crop.”
Seed borne diseases such as halo blight and tan spot can cause significant yield losses and are typically present each season. With both halo blight and tan spot being highly seed borne, pathogen exclusion is dependent on growers sourcing seed from crops that haven’t shown halo blight or tan spot symptoms.
The Australian Mungbean Association (AMA) approved seed scheme offers growers a low-risk seed option with production crops having been inspected for symptoms of halo blight and tan spot during the growing season.
Implementing farm hygiene practices also assists in minimising the spread of disease by restricting the movement of infected soil and crop residue.
Protection of the host relates to the disease resistance levels present in varieties. Varietal selection is an important tool in minimising disease risk, not simply for seed borne diseases but also the fungal disease powdery mildew which can lead to yield losses of up to 40 per cent in susceptible varieties if the disease becomes established prior to flowering according to Ms Kelly.
“Celera II-AU has the best levels of resistance to the halo blight pathogen, although this variety is suited to a niche market,” she said.
“Jade-AU and Crystal offer the best resistance to the tan spot bacterium, although heavy infection and yield loss can still occur under high disease pressure.
“Jade-AU offers the best resistance to the powdery mildew pathogen, although significant yield losses can still occur without the strategic use of fungicides.”
However, growers’ fungicide options are limited - currently there are no permitted or registered seed treatment options for the control of bacterial and fungal pathogens on mungbean.
Additionally, there are no effective chemical treatments for the control of the bacterial diseases, tan spot and halo blight, once they have established within a crop.
“Tebuconazole, and Custodia® (120 g/L azoxystrobin and 200 g/L tebuconazole) are currently available for use under APVMA minor use permits for the control of powdery mildew in mungbean (PER13979 (expires 30-June-2020) and PER82104 (expires 30-Nov-2022), respectively),” Ms Kelly said.
“Fungicides should be applied at the first sign of powdery mildew and then again 14 days later, if needed.”
She urged growers to closely monitor crops for early signs of disease as early detection can help avoid spreading the disease further throughout a crop.
Growers requiring diagnostic assistance can send samples to the Department of Agriculture and Fisheries. Plant samples should be wrapped in paper towel and placed in labelled zip-locked bags and sent via courier or express post to Lisa Kelly, DAF, 203 Tor St, Toowoomba Qld 4350.
For more information on the symptoms and management of halo blight, tan spot and powdery mildew, download a copy of Ms Kelly’s GRDC Update paper Integrated disease management in mungbean from the GRDC website www.grdc.com.au
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