Chickpea Ascochyta update what is happening in the paddock
Author: Kevin Moore, Leigh Jenkins, Paul Nash and Gail Chiplin (Department Primary Industries NSW) | Date: 24 Jul 2015
Take home message
- Localities where Ascochyta was found in 2014 are considered high risk for 2015 crops and growers are advised to apply a preventative fungicide before the first post-emergent rain event to all varieties including PBA HatTrick and PBA Boundary.
- From 27-30 June 2015, 49 chickpea crops in the Moree region were inspected for Ascochyta – the disease was NOT found in any crop nor in a paddock of volunteer chickpeas that were starting to pod.
- We believe the absence of detectable Ascochyta reflects judicious prophylactic management in high risk areas and lack of inoculum in low risk areas.
What’s happening in the paddock?
As of 25 June 2015, most chickpea crops in the GRDC Northern Region (NR) have had one decent rain event (lasting 2-3 days, up to 75mm); early sown crops have had two. Thus most NR chickpea crops have been potentially exposed to at least one Ascochyta infection event and early sown crops have been potentially exposed to two. In spite of these ideal conditions, Ascochyta blight, AB has not yet been detected in the limited area of the NR that has been surveyed to date. From 27-30 June 2015, 49 chickpea crops in the Moree region were inspected for Ascochyta – the disease was NOT found in any crop nor in a paddock of volunteer chickpeas that were starting to pod. A 3 July 2015 report of severe Ascochyta in crops of Kyabra east of North Star has yet to be confirmed.
Is there a new strain of Ascochyta?
Based on a very small number of isolates of the AB pathogen, Phoma rabiei (previously called Ascochyta rabiei), there is no evidence for a new strain. GRDC work has demonstrated clearly that isolates differ in aggressiveness but not in virulence (= strains, pathotypes, races). Isolates differ in aggressiveness if some isolates cause more damage than others; they differ in virulence if some isolates can infect more varieties than others or cause differential damage on varieties. Thus whilst an isolate from Yallaroi, NSW caused more damage on all four varieties used in the experiment than did isolates from Temora NSW, the Darling Downs QKD, Murtoa VIC, Donald VIC and Melton SA, all isolates infected all varieties. A new strain would exist if the Yallaroi isolate only attacked PBA HatTrick and say Kyabra but not the other two varieties OR the Yallaroi isolate caused more damage on PBA HatTrick than it did on Kyabra.
Where to from here?
Growers are urged to continue monitoring crops for Ascochyta 10-14 days after rain and to apply fungicides before the next rain event if warranted.
Most crops inspected to date (30 June) have had plant populations less than the minimum recommended 25 plants per sqm. If El Nino conditions develop in late winter - spring, as is predicted, these low plant populations and those conditions indicate Botrytis Grey Mould will not be a concern in 2015.
What alternative fungicides are effective against chickpea Ascochyta?
The large area of chickpeas planted in the NR this year and other forces have led to a shortage of registered products for chickpea Ascochyta. Pulse Australia has had discussions with suppliers and the APVMA regarding the issue of Emergency Use Permits, EUP. It is illegal to use any product that is not registered or currently under permit. EUP’s have been issued for certain products for the 2015 season. The following information is provided to help agronomists and growers make informed decisions about alternative fungicides for chickpea Ascochyta. Please check that a registration or EUP is in place before using any product.
The 2011 GRDC pulse fungicide initiative
Following the extreme 2010 season, GRDC and the agro chemical industry organised a series of standardised pulse fungicide trials throughout eastern Australia. The trials evaluated four products currently registered for other uses, and a coded product (MCW1086) each at three rates. In early August 2015, the APVMA issued Permits for three of these products for chickpea Ascochyta. This paper reports on the efficacy of those products at permissible rates from trials conducted at Tamworth in 2010 and 2011. The fungicides and rates were: Captan 800 WG® (captan) @ 1250g/ha 2011 trial (APVMA permit 81406); Amistar Xtra® (azoxystrobin + cyproconazole) @ 400mL/ha 2011 trial (APVMA permit 81470), and Prosaro® (prothioconazole + tebuconazole) @ 750 mL/ha 2010 trial (APVMA permit 81474). There were two control treatments (i) a low disease control based on the industry standard ie Unite 720 (chlorothalonil @ 1.0L/ha) and (ii) a high disease control where plots were not sprayed (Nil).
The 2010 trial (cv Jimbour) was inoculated with Ascochyta during a rain event on 17 June 2010; the disease progressed rapidly, killing unsprayed (NIL) plots by the end of July 2010. The 2011 trial (cv Jimbour) was inoculated during a rain event on 7 August 2011; the disease progressed throughout the season, killing unsprayed (NIL) plots by mid October. Key findings from the two trials were:
1. Under high Ascochyta pressure, there was no significant difference (P=0.05) in yield between 1.0L/ha Unite720 and Captan WG®, Amistar Xtra® and Prosaro®.
2. The effectiveness of the old chemistry captan; indeed the Ascochyta scores for Captan WG were as good as those for the Unite control. The 2011 trial confirmed a 2003 GRDC Tamworth trial that showed 1250 g/ha Captan 800 WG provided excellent control of Ascochyta.
Whilst the trials identified which products and rates gave satisfactory control of Ascochyta in a susceptible variety, under high disease pressure, the big take home message was:
Nothing was as cost effective or more efficacious as current commercial practice ie (Unite720 @ 1.0L/ha)
Department of Primary Industries, Tamworth, NSW
Ph: 02 6763 1133
Mb: 0488 251 866
Fx: 02 6763 1100
This research would not be possible without the considerable and ongoing support from growers and the GRDC for which we are most grateful. Thanks also to agronomists for help with the crop inspections and submitting specimens.
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Varieties displaying this symbol beside them are protected under the Plant Breeders Rights Act 1994.
GRDC Project code: DAN00143, DAN00176, UM00052
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