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Pulse Crop Update: Management of Ascochyta Blight in Chickpeas and Field Pea (07/04/19)

Ascochyta blight has been detected in three chickpea fields in Williams County (Figure 1) by NDSU pulse crop scout (Nicole Stanhope, NDSU Williston Research Extension Center).

Chickpea

Ascochyta blight has been detected in three chickpea fields in Williams County (Figure 1) by NDSU pulse crop scout (Nicole Stanhope, NDSU Williston Research Extension Center).

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Fungicide applications should be initiated when symptoms are first detected or, in the absence of symptoms, at flowering. Ascochyta blight lesions produce spores which spread the disease, so fungicides will provide the best control when applied prior to high levels of disease. The Ascochyta pathogen of chickpeas is very high risk for the development of fungicide resistance, so rotating and mixing fungicide modes of action is important for maintaining the efficacy of the fungicides available for managing this disease. NDSU researchers in Williston, Carrington, and Minot, ND regularly conduct field studies evaluating the comparative efficacy of fungicides for management of Ascochyta blight in chickpeas, and a combined analysis of the over 30 studies conducted from 2007 through 2018 indicates the following:

  • The Ascochyta pathogen has developed resistance to the Qol (FRAC 11) fungicides, and Headline (pyraclostrobin), Quadris and generics (azoxystrobin), and pproach (picoxystrobin) have no efficacy against this disease. Furthermore, premix products containing FRAC 11 chemistries will not provide additional control of Ascochyta blight in chickpea.
  • The DMI (triazole; FRAC 3) fungicides differ in their efficacy against Ascochyta blight. Proline (prothioconazole) is highly effective against Ascochyta blight, Quash (metconazole) has intermediate efficacy, and Quilt (propiconazole, a DMI + azoxystrobin, a QoI) has little or no efficacy. Proline exhibits a rate response, and applying Proline at 5.7 fl oz/ac confers better disease control than applying Proline at 5.0 fl oz/ac.
  • Prothioconazole can be applied as Proline or Delaro, which is a premix of prothioconazole (DMI; FRAC 3) and trifloxystrobin (QoI; FRAC 11). If applying Delaro, supplemental Proline should be added. When Delaro is applied at the labeled rate of 12 fl oz/ac, prothioconazole is applied 63 grams per acre. When Proline is applied at the labeled rate of 5.7 fl oz/ac, prothioconazole is applied at 81 grams per acre. In 2018, M. Wunsch, NDSU plant pathologist at the Carrington REC, received multiple reports of inadequate Ascochyta control in chickpeas when Delaro was applied at 12 fl oz/ac with no supplemental Proline. Applying Delaro at 12 fl oz/ac in a tank-mix with Proline at 1.25 fl oz/ac will result in prothioconazole being applied at 81 grams per acre, equivalent to Proline at 5.7 fl oz/ac.
  • The efficacy of Proline is significantly increased by tank-mixing with 1.38 pt/ac Bravo Weather Stik (chlorothalonil, FRAC M). Across five field studies conducted from 2015 to 2018 in Carrington, tank-mixing Proline with Bravo Weather Stik consistently improved Ascochyta management and chickpea yields under Ascochyta pressure (Figure 2). Bravo Weather Stik is a contact fungicide with no systemic movement, and nozzles and application pressures emitting fine droplets are recommended to maximize fungicide coverage and the efficacy of this tank-mix. Preliminary results suggest that tank-mixing Bravo Weather Stik with Delaro or with Miravis TOP (difenoconazole, FRAC 3 + pydiflumetofen, FRAC 7) may result in similar improvements in Ascochyta management.

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  • Among the SDHI (FRAC 7) fungicides registered for use on chickpeas, Priaxor (fluxapyroxad, FRAC 7 + pyraclostrobin, FRAC 11) is more effective than Endura (boscalid, FRAC 7) or Vertisan (penthiopyrad, FRAC 7). Priaxor and Proline have exhibited similar efficacy against Ascochyta blight of chickpeas when disease pressure is moderate, and Proline has been more effective than Priaxor when disease pressure is high.

 

  • Syngenta has several new fungicides registered for Ascochyta management in chickpeas. Because these products are new, none of the products have been evaluated extensively, but preliminary data suggests that Miravis NEO (a premix of pydiflumetofen, FRAC 7, and two other active ingredients with little or no efficacy against Ascochyta blight of chickpeas) may perform similarly to Priaxor and that Miravis TOP (a premix of pydiflumetofen and difenoconazole, FRAC 3) may perform similarly to Proline.

 

A summary of fungicide efficacy data for management of Ascochyta blight in field peas and chickpeas is available online at https://www.ag.ndsu.edu/carringtonrec/documents/plantpathologyrd/docs2019/2019-mondak-pulse-part-1 or by searching for “NDSU Carrington”, clicking on the link for “plant pathology” on the left side of the screen, and scrolling down to the PDFs of the talks given at the MonDak Pulse Day on Feb. 7, 2019.

See the 2019 North Dakota Field Crop Plant Disease Management Guide for a full listing of products registered for control of Ascochyta blight of chickpea in North Dakota.

 

Field Pea

Field Peas in the northwest part of the state have reached late vegetative to early reproductive growth stages. Bacterial blight was observed in several fields in Mountrail and McKenzie Counties earlier in June (Figure 3) but overall very little foliar disease has been observed in field pea thus far in the northwest region of the state.

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Bacterial blight symptoms can appear very similar to Ascochyta blight and it is essential to distinguish these diseases prior to making management decisions. Bacterial blight will not respond to fungicide applications. Resources to help differentiate symptoms of bacterial blight from Ascochyta blight are available in an article from a previous crop and pest report titled Bacterial Blight of Peas in North Dakota and Minnesota (06/11/15).

Note that the Ascochyta pathogen of field peas has also developed resistance to the QoI fungicides. The failure of the QoI fungicides was first observed in North Dakota in 2016 at the NDSU Carrington Research Extension Center and in a commercial field near Devils Lake in 2017, and pathogen resistance to the QoI fungicides at both sites has been confirmed by greenhouse and laboratory analysis. In field trials conducted prior to 2016, the fungicide Headline (pyraclostrobin, FRAC 11) conferred strong Ascochyta control in field peas; in field trials conducted subsequently, Headline has shown no efficacy (Figure 4).

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The geographic spread of QoI-resistance Ascochyta blight in field peas within North Dakota is unknown, but because the pathogen is readily disseminated long distances via infected seed and via long-distance movement of spores produced on overwintered field pea residues, it is likely that the QoI-resistant strains are widely disseminated. Where QoI resistance occurs, the fungicides Headline, Quadris and generics (azoxystrobin), and Aproach (picoxystrobin) have no efficacy. Proline is very effective against Ascochyta blight of field peas, and preliminary data suggests that Miravis TOP may perform similarly to Proline. The SDHI fungicides Endura and Vertisan are less effective than Proline, and where QoI resistance occurs, Priaxor is also less effective than Proline.

 

Lentil

Lentils are at late vegetative growth stages, and thus far, very little foliar disease has been observed. Fusarium root rot has been confirmed in both pea and lentil fields, although above ground symptoms are generally absent at this stage. As pod fill progresses, plants with high levels of root rot will begin to exhibit wilting, chlorosis and necrosis.

 

 

Audrey Kalil

Plant Pathologist, NDSU WREC

 

Michael Wunsch

Plant Pathologist, NDSU CREC

 

Julie Pasche

Associate Professor, NDSU

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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