With the 2017 growing season approaching, now is the time to set preventative practices in place to minimise the potential impact of disease in this year’s pulse crops. Ascochyta blight was a major issue for chickpea growers across the southern region due to changes in the virulence of the pathogen rendering all varieties susceptible to the disease. Early signs of changes in ascochyta blight on PBA HurricaneXT lentils were also noted in crops in the Mallala and Maitland regions.In addition, the ascochyta blight strain that can infect Farah faba beans is common across the mid and upper north of South Australia and has now been detected in the southeast region, on Yorke Peninsula and into Victoria. The ascochyta blight resistance in PBA Rana and PBA Zahra faba beans has also been compromised by this strain. Therefore, a thorough seed treatment and fungicide strategy is key for all pulse crops in 2017, combined with stringent monitoring for disease. Similarly, Cucumber Mosaic Virus (CMV) and Bean Yellow Mosaic Virus (BYMV) severely infected some pulse crops in the northern Yorke Peninsula and mid and upper northern regions. While these viruses are spread via the movement of aphids, it is generally too late to spray for aphids once the symptoms appear. However it is important to use seed free of virus infection.
Ascochyta blight of chickpeas
A virulence change in the ascochyta blight pathogen in southern Australia now means that all current chickpea cultivars are rated moderately susceptible or susceptible to infection. In spite of this, a range of chickpea types are now available offering growers the opportunity to exploit particular management and/or market opportunities, providing ascochyta can be managed effectively. Before choosing to grow chickpea in southern Australia, growers must consider their risk to ascochyta blight along with the ability to effectively control the disease. Both high and low rainfall regions are at risk as severe outbreaks can still occur in the latter in all current varieties in wet seasons such as 2016.
It is imperative that all chickpea seed is treated with a thiram based fungicide to prevent seed transmission of the disease onto the emerging seedlings in 2017. Moderately susceptible varieties will generally require 3 to 4 strategic fungicide sprays ahead of rain events, offering 2 to 3 weeks of protection, starting at 6 to 8 weeks post sowing. Susceptible varieties will require regular fungicide sprays every 2 to 3 weeks throughout the growing season ahead of rainfall events.
Ascochyta blight changes in lentils in SA
In 2016, ascochyta blight lesions were observed on the leaves of PBA HurricaneXT in a few crops in the Maitland and Mallala regions of South Australia. Ascochyta lentis isolates from these infected crops were tested by SARDI pathologists and found to cause a susceptible reaction in controlled environment tests on some varieties currently rated resistant including PBA HurricaneXT Although PBA HurricaneXT is currently rated as moderately resistant to ascochyta blight, the rapid uptake of the variety, particularly on the Yorke Peninsula, threatens the longevity of the ascochyta blight resistance in this cultivar. Disease reactions were also observed on PBA Ace (currently rated R) and PBA Bolt (currently rated MR) in the tests, although field reactions have not been confirmed on the latter two cultivars.
In 2017, growers in these regions should manage these varieties as higher risk for ascochyta blight. It is important to diversify variety selections within a year and across rotations to maintain the stability of resistance systems and reduce the risk of crop failure. In particular, growers should use a thiram based seed dressing, plan for a fungicide spray during podding and monitor the crop closely in case in case additional sprays are required during the season.
Ascochyta blight in faba beans in SA
Faba bean cultivars have not changed reactions to AB since 2015 and testing of Ascochyta fabae isolates in shadehouse trials has identified 3 reaction groups: Farah is moderately susceptible to AB in the Lower to Upper North of SA, PBA Rana and PBA Zahra are partially compromised, while PBA Samira and Nura remain resistant. Testing of a smaller set of isolates collected in 2016 have confirmed that these new pathotypes are also starting to become established in the Yorke Peninsula and South East growing regions. A three spray fungicide strategy is now required to control AB in Farah, while podding sprays should be planned for PBA Rana and PBA Zahra to prevent pod and seed infection.
CMV and BYMV infection of pulse crops
Cucumber Mosaic Virus (CMV) and/ or Bean Yellow Mosaic Virus (BYMV) severely affected chickpea, lentil and lupin crops in the Yorke Peninsula and mid to upper northern regions in 2016. Transmitted during the spring flights of aphid hosts, symptoms of yellowing and/ or stunted plants were seen in chickpeas and lentils affected by CMV. Lentil crops presented with blackened tillers and wilting plants, mostly caused by BYMV.
For non-persistently transmitted viruses such as CMV and BYMV, it is generally too late to spray for aphids once virus symptoms appear. To limit disease risk the following year, however, seed should not be kept from infected crops and CMV is also seed transmitted. If retaining seed from either infected or neighboring crops it is essential that the grain is tested for virus infection prior to sowing.
Websites for Plant and Seed testing laboratories for viruses
- DDSL Seed testing and certification (Perth)
- Crop Health Services, AgriBio Centre, Bundoora, Victoria (Melbourne)
- TASAG ELISA Testing Services (Hobart)