Cereal disease update and use of fungicides on fertiliser and seed

Author: | Date: 27 Feb 2014

Hugh Wallwork,

SARDI

Take home messages

  • Net blotch is evolving rapidly and needs monitoring to provide early warning of further changes. New seed treatments are likely to provide some control in future.
  • Growers need to use resistance and fungicides carefully to avoid future changes in pathogen virulence and fungicide resistance.
  • Crown rot and take all need to be remembered when planning rotations. Understanding inoculum survival and increase will help in management decisions, as will the use of PredictaB tests.
  • The choice of fungicide treatments at seeding is very important for managing diseases on farm as well as across a region.

Net form net blotch (NFNB)

Net form net blotch continues to cause problems in many barley crops. In some areas growers are treating crops with fungicides from very early growth stages and finding that this form of protection is most effective. A particular concern with NFNB is the continuing rapid evolution of virulence in this pathogen with Keel, Maritime, Fleet and Oxford showing rapid falls in resistance rating in recent years.

In 2013 the main feature of the epidemic was the severe virulence on Fleet in many areas. Until 2012 Fleet was largely very resistant but isolated crops at Urania and south of Port Pirie showed high levels of infection. Extensive testing of isolates of the fungus taken across SA in recent years has shown that none of the strains tested have combined virulence on Fleet and Maritime so in some areas Maritime may have appeared as quite resistant. However, virulence on Maritime remains present in areas where this variety is still grown.  Virulence on Commander, Fathom and Navigator was also very common. Two Fleet isolates from Wokurna and near Pt Broughton also showed virulence on Oxford, Skipper, SY Rattler, Westminster and Wimmera. In contrast, Buloke, Grange R, Hindmarsh, Scope, Schooner and Sloop SA have shown consistently good resistance so far. Compass has shown good resistance in the field but testing in controlled conditions indicates that some isolates cause moderate susceptibility.

In the future improved control of this pathogen is most likely to come from new seed treatments that have shown promise in 2013. It will remain most important however that the more susceptible varieties are not grown in areas or situations prone to the disease as this only facilitates the further evolution of the fungus to increased virulence and possibly fungicide resistance.

Spot form net blotch (SFNB)

NVT trials over many years have indicated that spot form net blotch causes little damage to barley crops except where the most susceptible varieties are grown in the most prone situations. It therefore came as a surprise that some crops, notably Hindmarsh, saw severe infection levels in some areas that most likely led to significant yield losses. Of particular concern were Scope crops around Loxton and Cleve that showed susceptibility similar to Hindmarsh (S) whereas in previous years, and at most NVT sites in 2013, Scope has rated as only moderately susceptible. This is currently being tested in controlled environment conditions on the Waite Campus.

It is most likely that SFNB was more severe in 2013 because of the widespread cultivation of Hindmarsh combined the warm conditions in May and subsequently warmer and wetter winter than usual.

Crown rot and take-all

Good spring rainfall in 2011 and 2012 together with dry summers contributed to an increase in crown rot and take-all in 2013. It will be important to know the levels of these diseases in paddocks at the start of 2014 to plan management which reduces the risk of yield loss from crown rot and take-all in cereal crops this season.

Crown rot was favored by high levels of inoculum carried over from 2012 followed by ideal conditions for infection at the start of 2013. Relatively dry conditions during grain fill in many areas, particularly the upper Eyre Peninsula, then resulted in white head expression and yield losses from crown rot.

Take-all appeared as a problem on upper/eastern Eyre Peninsula, particularly around Cleve, in 2013. The fungus requires wet spring conditions to build up, as occurred in 2010 and 2011. Although the dry spring in 2012 would not have increased inoculum, the dry conditions through spring and summer likely prevented break down of the inoculum. The Cleve experience is a timely reminder that it only takes 1-2 seasons with conducive conditions for take-all inoculum to build up to potentially damaging levels.

White grain

White grain was not detected in deliveries to silos in 2013 and there was only one report from upper Eyre Peninsula of grain retained on-farm for feed which had very low levels of white grain. The absence of white grain was likely due to most spore release occurring prior to head emergence (Figure 1) and relatively low humidity conditions from head emergence to the end of grain fill in areas prone to this problem.

Also as a result of the dry spring, there were no obvious white grain symptoms in the SAGIT variety screening trials on upper Eyre Peninsula. Similarly there were no symptoms of white grain in any of the NVT trials sown in SA. This means we still have no indication of the resistance levels of current cultivars or of possible sources for resistance genes. We artificially inoculated pot trials on the Terraces at the Plant Research Centre in 2013 and although we have not yet processed the samples, preliminary assessment suggests artificial inoculation may provide an avenue for future resistance screening.

Identification of symptoms of infection by the white grain fungi in green cereal heads is possible but not easy in the field due to their similarity to symptoms of frost damage.

Spore traps at Buckleboo on upper Eyre Peninsula indicate that spores were released from stubbles from the first week in August to the first week in September, but were not present in significant numbers after that (Figure 1). Trends in spore release were similar for both sites (approximately 1 km apart) which were monitored, although spore numbers were lower in the paddock where there had been a break from cereal in 2011. This indicates that a break from cereal will contribute to reduced infection levels and that spore trap results could be used prior to harvest to predict the risk of white grain in crops.

Figure 1. Presence of air-bone spores of the fungi associated with white grain in two paddocks at Buckleboo during 2013.

Figure 1. Presence of air-bone spores of the fungi associated with white grain in two paddocks at Buckleboo during 2013. 

Fungicides at seeding - Wheat

The large area sown to Mace has seen a significant proportion of this variety protected with in-furrow fungicide treatments. This reduces the need to spray the crop until flag leaf emergence and, if used widely enough, will likely provide enough early control to avoid the need for any foliar fungicide sprays since the rust will have insufficient host area to build up and create an epidemic. In other words, the more people use an in-furrow or fluquinconazole treatment, the more effective they will be.  There is a temptation based on the experience of the past two seasons to think that stripe rust is not a problem with Mace. That may well change if the widespread vigilance to control the disease is reduced and if seasonal conditions are more favourable for survival and spread of the fungus.

A fluquinconazole seed treatment should provide a similar level of control of stripe rust to flutriafol applied in–furrow but has the added advantage that it will also control the smuts, whereas in furrow treatments do not and will have to be applied separately. The former however, is more expensive.

Where growers are seeking suppression of Rhizoctonia, then one of five new seed treatments; EverGol Prime®, Vibrance®, Rancona Dimension®, Dividend M® or Tri-Power®, can be used. These will not control stripe rust so where both diseases are a concern then an in-furrow treatment will be required for stripe rust control.

Fungicides at seeding - Barley

All barley crops should be treated with a product that controls powdery mildew. Failure to do so will allow this disease to build up and possibly mutate allowing it to overcome some of the current fungicides that the industry relies on. Powdery mildew is particularly prone to the development of fungicide resistance. Such a breakdown has already occurred in Western Australia and needs to be prevented from happening in Eastern Australia.

Where growers seek to suppress Rhizoctonia in barley then, as in stripe rust in wheat, separate fungicides will need to be applied for the mildew control.

Loose smut

Numerous Hindmarsh barley crops across Southern and Western Australia showed loose smut infection. In many cases this occurred in spite of treatment with seed fungicides that should have controlled infection. Presumably Hindmarsh is too susceptible for some treatments to be effective. Tests are underway in SARDI on infected seed to determine which seed treatments are capable of providing adequate control in Hindmarsh.

Contact details

Hugh Wallwork

08 8303 9382

hugh.wallwork@sa.gov.au

GRDC Project Code: DAS00099; DAS00139,