Cereal pathology watch list for 2016

Eyespot

Eyespot causes lodging in cereal crops. It recurred as a problem in 2015 despite low rainfall conditions not being conducive to infection with this disease. The area affected now includes the Yorke Peninsula and around Cleve, particularly the Cleve Hills where a number of wheat crops lodged badly last year.
 
The main control strategy used for eyespot management overseas is fungicide application early in stem elongation. However, no fungicides are currently registered for managing eyespot in cereals in Australia. Trials undertaken in South Australia (SA) in 2014 and 2015 gave results which indicate fungicide efficacy is consistent with overseas experience. 

Data from these trials should lead to label extension/registration for one or more products for control of eyespot in cereals in Australia in 2016.

Screening trials undertaken in 2014 and 2015 have demonstrated that a range of resistance levels is present in current South Australian cereal varieties. The trials have provided information for varietal choice and for future breeding programs. 

The bread wheat varieties Mace, Axe, Shield, Cobra and Corack should be avoided where eyespot is known to be a problem. Preliminary evidence also suggests the durum variety SaintlyA is also quite susceptible. The barley varieties La Trobe and Hindmarsh should also be avoided in prone areas. 

Septoria tritici blotch

Septoria tritici blotch is a fungal disease that can disperse over large distances early in the year when airborne spores are produced on infected wheat stubble. Subsequent infection only spreads by rainsplash within the crop leading to hotspots of disease leaves where initial infection levels were low.  

The disease had been developing as a serious problem in the south east of SA due to increased wheat cultivation with closer rotations, although dry springs helped to greatly suppress septoria damage in the past two seasons.

In 2015 the disease was observed over a wide area throughout the mid and high rainfall regions of SA. In hindsight, it is apparent that the disease must have become established in one or more wheat crops between the Tothill and Bluff Ranges north west of Eudunda during 2014 or earlier. This is despite not being noticed or reported in those years.

This conclusion arises from the uniformity and high levels of infection observed across several neighbouring crops in 2015.  It is quite likely that infection from this area was responsible for the further spread of the disease to other areas of the Mid-North, Yorke Peninsula and eastern/lower Eyre Peninsula in 2015. In all these latter areas the disease was observed as small hotspots of infection, which suggests a recent introduction of infection from a more distant location. 

Most of the infection was reported on the variety Mace. Prior to these observations Mace had shown good resistance to fungal isolates collected in SA, although it had been observed to be susceptible in the South East in 2014 and also in the high rainfall areas of South West Victoria.

As well as increased virulence on Mace the recently identified septoria population has increased virulence on other related varieties to the point that few of the commercial varieties can now be expected to escape infection if sown early in areas where inoculum is present.
 
Growers should therefore now take greater care with this disease, especially when growing the most susceptible varieties in prone areas. These include Axe, Corack, Darwin, Emu Rock, Grenade CL+, Hatchet CL+, Impala and Mace.

Foliar fungicides registered to control this disease are available, but they are not as effective as we would like and there is a threat of fungicide resistance developing, especially with the strobilurins if they become used too frequently and when disease levels are high. 

The best management strategy remains the avoidance of the most susceptible varieties, particularly with early sowing.

Loose smut

Loose smut has continued to appear in Hindmarsh barley crops throughout SA. This past year has also seen some infection of Scope crops on the Eyre Peninsula. In most of these instances seed treatments were applied including treatments registered for the control of loose smut. Seed treatment tests conducted by SARDI have shown that products containing just triadimenol provide only about 50 per cent control of loose smut in Hindmarsh.

Products containing flutriafol and tebuconazole as well as the low rate of Rancona Dimension® (80 ml) also allow some infection to persist in crops. 

Effective control is provided by products containing carboxin and the new SDHI fungicides; Evergol Prime® and Vibrance®. Where seed is known to be infected then the higher rates of SDHI fungicides set for rhizoctonia control should be used. The higher rates ɸ of Rancona Dimension® should also provide effective control for loose smut . Crops of La Trobe barley are likely to show similar susceptibility as Hindmarsh.

ɸ Higher rates are not registered for control of loose smut, only the one rate

Growers should be aware that use of seed treatments for the control of barley mildew should continue as a high priority for effective long term management of this disease. Where control of Rhizoctonia or loose smut is a priority growers planning on using treatments specific for these diseases should consider mixing it with triadimenol or flutriafol for mildew control unless they know their barley variety has good mildew resistance.

Red leather leaf

Red leather leaf was observed to cause significant leaf damage to oat crops in the Marrabel Valley. This was likely due to the wet conditions in September combined with close oat rotations in the valley. Most of the infection was in Mulgara oats, this variety being popular in the area rather than because it is particularly susceptible. Control with fungicides is not an option available so avoiding the most susceptible varieties is important. Development of improved resistance should be a priority and we are developing fungal culturing and plant screening techniques for this purpose.

Crown rot

Crown rot was not a significant problem in 2015, but the low rainfall is likely to have slowed break-down of infected cereal residues. This means that non-cereals used as a break to reduce crown rot inoculum may not have been as effective as expected. Consider soil sampling to assess the risk of yield loss from crown rot prior to sowing susceptible crops such as durum wheat in 2016.

Acknowledgement

Funding for this work was provided through the GRDC Project DAS00139 and their support gratefully acknowledged.

Contact details

Hugh Wallwork 
Plant Research Centre 
SARDI
Gate 2b Hartley Grove, Waite Campus
08 8303 9382

Margaret Evans
Plant Research Centre 
SARDI
Gate 2b Hartley Grove, Waite Campus
08 8303 9379

GRDC Project Code: DAS00139,