Managing Mycosphaerella (Ascochyta) Blight
The main disease to be controlled by foliar fungicide in peas is mycosphaerella (ascochyta) blight (Figure 1). Fungicides also offer control or suppression of white mould, powdery mildew and rust, depending on the product. However, these diseases are less frequent and less severe in Manitoba-grown peas. Scout for mycosphaerella symptoms from V10 (10th node) to R2 (beginning bloom), during 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. The goal is to get good fungicide coverage on 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 Fungicide Research Results
MPSG’s On-Farm Network has conducted 19 trials since 2017 evaluating the effectiveness of foliar fungicide application in peas for control of mycosphaerella blight. This study includes:
- One fungicide application at early flower (R2) vs. no fungicide (untreated) – 11 trials in total
- One fungicide application at R2 vs. two fungicide applications (first application at R2, second application 7 to 14 days later) – 6 trials in total
- All three treatments – single vs. double vs. untreated – 2 trials in total
To date, four out of 11 trials have resulted in significant yield increases from single application compared to untreated peas (Figure 2). Two out of six trials showed a significant yield increase from double fungicide application compared to single application (Figure 2). Of the two trials that compared all three treatments, one showed significant yield differences between treatments. At this trial, both single and double fungicide application significantly increased pea yield compared to untreated peas. However, double and single fungicide treatments yielded similarly to one another (Figure 2).
Environmental conditions at each location influenced pea yield response to fungicide application. Sites that were conducive to mycosphaerella development had a greater likelihood of showing a yield increase from fungicide. In 2017, 2018 and 2019, dry conditions at the time of flowering at most sites resulted in low disease pressure overall. As mycosphaerella development is very weather-dependent, it is important to evaluate environmental conditions ahead of fungicide application to determine your own personal risk versus reward.
Small Plot Fungicide Research Results
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.
Foliar Disease Survey Results
In 2019, 44 pea fields were surveyed during mid- to late- July when peas were at the podding stages (R3 to R4) (Table 2). The severity of mycosphaerella blight, white mould and anthracnose were estimated using a visual scale of 0 (no disease) to 9 (whole plant severely diseased). Powdery mildew, downy mildew, rust and bacterial blight were rated as the percentage of foliar area infected.
Similar to previous years, mycosphaerella (ascochyta) blight was the most prevalent foliar disease and was present in all pea fields surveyed. Disease severity ranged from 2.3 to 6.3, averaging 3.8. The impact of disease severity on yield will depend on how early the disease sets in and how quickly it develops.
Downy mildew was detected in 64% of fields (29/44) and the percentage of leaf area infected averaged 0.4%. Bacterial blight was observed in 39% of the crops surveyed (17/44) with the percentage of foliar area infected averaging less than 0.1%. White mould, powdery mildew, rust and anthracnose symptoms were not observed in any of the fields surveyed in 2019.
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)