Protecting WA crops

GRDC Perth Research Updates 2023 – Pathology - Part 2

In this issue of Protecting WA Crops we continue our coverage of the plant pathology research topics presented and written by Department of Primary Industries and Regional Development (DPIRD) staff for the 2023 Perth GRDC Research Update’s held in February.

To read about the invertebrate research or other disease and virology research covered by DPIRD staff refer to the previous Protecting WA Crops newsletter Issue 28 and Issue 29.

Impact of fungicide product, rotation and timing on Net form net blotch in Planet barley in southern WA

Net form net blotch. Image: DPIRD
Net form net blotch. Image: DPIRD

At a glance:

  • Net form net blotch (NFNB) was widely distributed across south coast WA in 2022.
  • Greater virulence for Planet barley is apparent in NFNB.
  • Foliar fungicide spraying on established crops reduced NFNB.
  • The best impact on yield was seen when fungicide was applied early in epidemic development, application at growth stage Z31 (early stem extension) increased yields by 13 per cent as compared to the control.

Net form net blotch, caused by the fungus Pyrenophora teres f. teres, occurs throughout barley growing areas of Western Australia. Severe NFNB infection can cause up to 45 per cent reduction of yield in barley crops, in addition to affecting the grain quality. NFNB infection is most commonly spread via infected stubbles but can also be seed borne. Spores produced on stubble are spread via wind to new barley crops, therefore crops sown onto or adjacent to barley stubble are at the greatest risk.

In recent times, NFNB has become more virulent across the south coastal production zone. The barley variety Planet is widely grown in this area and is susceptible to the Oxford NFNB pathotype which is dominant in this zone. This led to Albany based DPIRD research scientist Dr Kithsiri Jayasena investigating NFNB foliar fungicide control options in trials in 2022.

Planet barley was sown in a block with Uniform®-in-furrow. Six foliar fungicide treatments were applied during the following Zadoks (Z) growth stages to determine their impact on NFNB disease levels:

  1. Z31 only. Sprayed with Prothioconazole.
  2. Z39 only. Sprayed with Prothioconazole.
  3. Farmer practice - Z31 (Tebuconazole with Prothioconazole) and Z39 (Prothioconazole with Bixafen).
  4. Threshold based system - Z39 (Prothioconazole) and Z59 (Propiconazole with Azoxystrobin or Propiconazole with Benazovindiflupyr) applied when the top three open leaves reached an average 10% disease severity.
  5. Standard practice - Z31 (Prothioconazole) and Z39 (Prothioconazole)
  6. Full control - Z31 (Prothioconazole), Z39 (Propiconazole with Azoxystrobin or Propiconazole with Benazovindiflupyr) and Z56 (Propiconazole with Azoxystrobin).

The trial site had very high NFNB disease pressure, and Dr Jayasena found that Uniform®-in-furrow alone was not sufficient to protect the crop up to flag leaf emergence. Uniform®-in-furrow is registered for 90 days suppression of NFNB. Only one per cent disease severity was observed at Z31, but by the early dough stage (Z83) 82 per cent of the area of the top three leaves was affected by NFNB. The application of foliar fungicides at Z31 and double spray at Z31 and Z39 reduced NFNB disease pressure by 10 and 14 per cent, respectively, compared to untreated control on the top three leaves on average.  There was no significant difference in the grain yield between an early spray at Z31 and a two-spray strategy in this trial.

The threshold-based system and the full control fungicide application systems in this trial reduced the amount of NFNB disease; however, there was significant impact on grain yield compared to the control.

Under high disease pressure, with favourable environment and very susceptible variety, multiple fungicide applications were required. Intervention early in the epidemic development (eg. Z31 application) gave the greatest yield response. The threshold-based system used in this experiment was not as effective as the standard practice. NFNB disease was allowed to reach uncontrollable levels before intervention in the threshold-based system. Dr Jayasena believes that in this environment the threshold should be revised to be less than 5 per cent disease severity.

More information on NFNB and foliar fungicide applications for management can be found in Mr Jayasena’s Research Updates paper Impact of fungicide product, rotation and timing on Net form net blotch in Planet barley in southern WA

For more information on NFNB refer to DPIRD’s Managing net from net blotch of barley in Western Australia webpage.