Summer disease risks threaten mungbeans

Diseases in mungbeans are placing pressure on yields and annual disease surveys, field observations and diagnostic samples show that disease continues to cause significant constraints to the industry.

This is a key finding of collaborative GRDC and QDAF disease research investment, which has provided some hands-on advice for northern growers trying to avoid losses from some of the more common mungbean diseases.

Researchers list halo blight, tan spot and powdery mildew as some of the major causes of loss to mungbean growers, while soil borne diseases such as fusarium wilt appear to be increasing in incidence and severity. Recent cropping seasons have also seen major outbreaks in phytoplasma.

DAF’s Toowoomba-based plant pathologist Lisa Kelly said that a combination of poor host resistance, virulent pathogens, and ideal weather conditions would allow pathogens to infect crops and cause significant losses for northern growers.

“Powdery mildew has been shown to lead to yield losses of up to 40 per cent in susceptible varieties, when the disease becomes established prior to flowering,” Ms Kelly said.

“Two trials were undertaken during the 2016-17 season to determine the best fungicide management strategy for the control of powdery mildew using different fungicides on the variety Jade-AU, and using different row spacings.

“Results from trials at Missen Flat, south of Toowoomba support previous findings that spraying at the first sign of disease and again 14 days later is an effective management strategy.

“The results presented also indicate that there is an option to spray once the disease is one third of way up the plant and then 14 days later if that initial sighting of disease is missed.

“These same treatments options also had the lowest disease severity ratings at 76 days after emergence. Both fungicides resulted in large increases in yields compared to the untreated plots, particularly in the treatments sprayed more than once.”

The fungicides Folicur 430 EC and Custodia 320 SC were applied as a part of the trial.

Fusarium wilt, halo blight and tan spot were also highlighted in the update.

Ms Kelly said that fusarium wilt was estimated to cost the mungbean industry in the vicinity of at least $4.3 million per annum through lost production.

“Yield losses attributable to fusarium wilt have been estimated to be as high as 80pc in affected paddocks, causing huge losses to individual growers and the mungbean industry,” Ms Kelly said.

“Recommendations are that growers avoid paddocks with a history of disease, sow seed into well-drained soils, and avoid plant stress where possible.

“To minimise the risk of halo blight and tan spot, the recommendations are to use low risk planting seed, plant varieties with higher levels of resistance, clean harvesting equipment, control weeds and volunteers, and use suitable crop rotations,” she said.

In recent years there have been outbreaks of phytoplasma in a number of crops throughout the northern grains region. Phytoplasma are specialised bacteria that infect plants, and are spread from plant to plant by insect vectors, such as leaf hoppers.

Ms Kelly said that was it unclear what the underlying reasons were for this sudden increase in phytoplasma disease incidence.

“During the 2016-17 summer, phytoplasma was widely reported in mungbean, soybeans, peanuts and pigeon pea from north Queensland to central NSW. In some of the worst crops 60 to 90pc of plants were infected, whilst others had a lower infection of 10 to 15pc,” she said.

“Further research and paying close attention to any new infestations is vital to gain a better understanding of the disease and its insect vector and develop strategies to minimise damage.

“Growers should monitor crops for leafhopper activity and phytoplasma infection, and report any outbreaks to DAF Entomologists and Pathologists.”

CLICK HERE for more information on the biology, symptoms and management of these bacterial diseases.