A Message from Mary Burrows, MSU RE: Ascochyta Blight of Pea Found in Sheridan County. Cropland disease. Ascochyta blight of pea found in Sheridan County. Thanks to all my hosts in northern Montana this week: we’ve been finding some disease among the nutrient deficiencies! The most important of these is Ascochyta blight in pea. A picture is below. Note the ROUND spot on the left with tiny black spots (whip out that hand lens) in the center is Ascochyta blight. The ANGULAR lesion on the right is from a neighboring field with Bacterial Blight. Remember that you need to discriminate between these diseases, ask questions since you can spray a fungicide for Ascochyta – there’s nothing you can do for bacterial blight. Bacterial blight follows hail or hard rains that wound the plant tissue. If there’s not high humidity or more splash dispersal, often this damage is restricted to the tissue present when the event occurred. A hint is that you see most of the damage on one side of the plant, where the wind was coming from. Early in the infection you’ll see ‘watersoaking’ or translucent tissue where the bacteria is basically dissolving cell walls so they leak all over. Later, they turn brown and dry and are often confused for fungal leaf diseases. The key is that the lesion stops at leaf veins, making the typical ‘angular’ lesions. You can often see a shiny shellac of bacteria where it oozed from the wound and dried. This reflects in the sun and is a pretty reliable indicator of bacterial, not fungal, infection. Both types of pathogens CAN be on the same plant, don’t get me wrong, but usually in my experience one clearly predominates. Ascochyta blight will expand and cause lesions with concentric circular rings of pycnidia (fungal structures containing spores) that expand and defoliate the plant. Ascochyta blight, given ideal environmental conditions (humid, wet, and warm, preferably with rain) will spread even in the absence of rain showers. Pea and lentil are more resistant/tolerant of infection than kabuli chickpea, but this early in the cropping season and with the near‐daily rain showers up here in the NE are pretty ideal conditions for disease development. At this time, as a preventative measure, growers should scout fields and start planning for a fungicide application. Normally a good time for application is when flowering starts, but if you have significant disease pressure you should apply prior to flowering. The Canadians have a hard time showing a good correlation between fungicide application and yield benefit since peas do compensate (put on branches, pods etc. to make up the lost tissue), but in chatting with them, if disease development leads to stem lesions and stem breakage, there’s a good chance you’re going to receive a yield benefit from an application. Choices include Headline, Priaxor, Quadris, and Proline – I don’t prefer any over the other. Data can be found on Michael Wunsch’s report at ag.ndsu.edu/carringtonrec/agronomy‐1/research‐documents/plant‐pathology/2011‐field‐evaluation‐offungicides‐ for‐management‐of‐mycosphaerella‐ascochyta‐blight‐on‐field‐peas‐summary More information on this disease than you ever wanted to know: plantmanagementnetwork.org/pub/php/diagnosticguide/2011/pea/ A pretty publication you can get from MSU or your county agent: msuextension.org/store/Products/Diseases‐of‐Cool‐Season‐Legumes‐(Pulse‐Crops‐‐Dry‐Pea‐‐Lentil‐and‐ Chickpea)__EB0207.aspx Dolores Rohrich Membership/Communications Director Northern Pulse Growers Association 1710 Burnt Boat Drive Bismarck, ND 58501 701-222-0128 rohrich@northernpulse northernpulse
Posted on: Mon, 17 Jun 2013 14:28:40 +0000
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