Managing Ascochyta/Mycosphaerella Blight
The main disease to be controlled by foliar fungicide in peas is ascochyta/mycosphaerella blight (Figure 1). Fungicides can also offer control of Sclerotinia and downy mildew, but these diseases are less frequent and less severe in Manitoba-grown peas. Scout for mycosphaerella symptoms from V10 (10th node) to R2 (beginning bloom), from mid-June to late July.
Foliar fungicide application for control of Mycosphaerella blight should be made at early flower, when one flower is open on most plants across the field (Figure 2). Note that peas flower from the bottom up. The goal is fungicide coverage of the leaves in the lower canopy. This means spraying just before the canopy begins to close.
If symptoms spread into the mid to upper canopy and warm, humid weather persists, consider a second fungicide application 10-14 days later using a different mode-of-action.
To aid the decision of whether or not to apply fungicide, follow the worksheet below to determine your risk level of mycosphaerella blight development:
On-Farm Network Field Pea Fungicide Research
Manitoba Pulse and Soybean Growers conducted field-scale On-Farm Network trials to investigate the yield response of field peas to foliar fungicide application in 2017 and 2018. Three trial types were established using replicated strip trials:
- Single application applied at early flower (R2) vs. no fungicide (untreated).
- One fungicide application at early flower vs. two fungicide applications, applied first at early flower and a second application 7 to 14 days later.
- The third trial expanded on this and added untreated strips to compare with both single and double applications.
One Fungicide Application
On average, a single application of foliar fungicide increased yield by 2.7 bu/ac when compared with the untreated check. In the third trial, a single, early application of foliar fungicide increased yield by 5.9 bu/ac compared to the untreated check (Table 1).
Two Fungicide Applications
Yield response to two applications versus a single application of foliar fungicide depended on the site-year. Three out of six sites had a significant yield increase for two applications compared with a single, early application. In the case of these three fields that responded to fungicide, environmental conditions were conducive to disease development, increasing the likelihood of a yield response.
In 2017, dry conditions resulted in low disease pressure. Conditions were similar in 2018, where the lack of moisture once again limited disease development. Sites with greater rainfall often had higher disease pressure. As mycosphaerella blight is weather-dependent, it is important to evaluate environmental conditions and your own risk versus reward.
These trials are continuing in 2019 to assess disease severity across treatments, encompass more environments and refine foliar fungicide recommendations.
A small-plot study testing various pea inputs was conducted at Minto and Hamiota in 2015 and 2016. These trials tested no fungicide vs. one application (Headline EC at 10% flower) vs. two applications (Headline EC at 10% flower + Priaxor 12-13 days later).
In 2015, there was a significant effect of fungicide application compared to no fungicide. However, there was no difference between one application and two applications of fungicide (Table 2). At Hamiota (2016), there was a significant yield response to two applications of fungicide and no response to one application of fungicide. At Minto (2016), there was a significant yield response to both one and two applications of fungicide. Two applications of fungicide resulted in the highest yield; however, the overall yield potential was low at this site.
Managing Ascochyta Blight in Field Peas – Pulse Beat Issue 87, The Pea Report by Serena Klippenstein (MPSG)
The Effects of Seeding Rate and Fungicide Application on Field Peas in Manitoba – Manitoba Agronomists Conference poster, Greg Bartley and Laryssa Stevenson (MPSG)
Fungicide Decision Support Checklist for Ascochyta & Mycosphaerella Blight in Pea – Saskatchewan Pulse Growers fact sheet by Sherrilyn Phelps (SPG), Sabine Banniza (University of Saskatchewan) and Faye Dokken-Bouchard (Saskatchewan Ministry of Agriculture)