Foliar Wheat Disease Management with Fungicides – 2022: Report 2
Categories: Fungicides
COOPERATORS: Meriem Aoun1, Brian Olson1, & Tyler Pierson2; Departments of Entomology & Plant Pathology1, Field Research Services Unit2; Oklahoma State University, Stillwater, OK
PURPOSE: To determine the efficacy of fungicides for controlling foliar diseases when applied to hard red winter wheat in Oklahoma.
LOCATION: Entomology & Plant Pathology Research Farm; Stillwater, Oklahoma (Google Maps coordinates: 36.1266690, -97.1047885)
VARIETY: ‘OK Bullet’
SOIL TYPE: Norge loam
PLANTING DATE & RATE: 15-Oct-2021 at 90 lb/ac
FUNGICIDE APPLICATION DATE(S):
A total of 12 fungicide treatments ( from Albaugh LLC) were applied on 30-Apr-2022 at Feekes’ growth stage 10.1 (wheat heads (awns) just starting to emerge from the boot). There was an untreated check.
TARGET DISEASES: Powdery mildew, leaf rust, stripe rust, Septoria leaf blotch, spot blotch, and tan spot.
PLOT DESIGN: Plots were 49 in. (7 rows; 7 in. spacing) by 20 ft, replicated four times in a randomized block design. Data were analyzed using R version 4.1.3. Mean separation (LSD) was conducted only if ‘F’ test was significant.
CULTURAL PRACTICES:
Fertilizer: Fertilizer was applied to the soil with a 50 bu/ac yield goal.
Herbicide: None applied
Insecticide: Gaucho 600 (2.4 fl oz/cwt) applied as a seed treatment
Irrigation: No irrigation provided
METHOD OF APPLICATION: Fungicides were applied with a CO2 wheelbarrow sprayer as a broadcast foliar application using flat fan nozzles (8003EVS) spaced 18 inches apart. The sprayer was calibrated to deliver fungicides at a rate of 20 GPA.
DISEASE ASSESSMENT: When sufficient foliar disease was present, plots were evaluated for type of disease and rated for percent infection using modified keys based on, “A Manual of Assessment Keys for Plant Disease. 1971. Clive James. Canada Department of Agriculture Publication No. 1458.” In this rating system, the percentage of leaf surface area covered by a disease was rated as 0=no disease; 1=1% infection; 5=5% infection; 10=10% infection; 15=15% infection;25=25% infection; 40=40% infection; 65=65% infection; 80=80% infection; 90=90% Infection; 99=99% infection.
GENERAL OBSERVATIONS: Drought was prevalent through most fall 2021 and spring 2022. The accumulated rainfall in spring of 2022 was 15 inches in March-May 2022. Prior to planting (July-September 2021), the accumulated rainfall was 4.2 inches. Moisture in October-November (5.37 inches) promoted emergence and stand development. During spring, the highest levels of moisture were recorded in May 2022 (10.55 inches) which helped crop development and seed fill.
Low levels of barley yellow dwarf (BYD; confirmed with ELISA testing) infections were present but scattered randomly across the trial. Although BYD may have slightly impacted yield it was not a major concern. Powdery mildew (PM) was the most prevalent disease in April and May and was severe especially in lower and mid-canopy. PM was rated on 19-April (before fungicide application ( Table1, Figure 1) and on 19-May (after fungicide application, which was on 30-April) (Table 1, Figure 2). Leaf spot, mainly spot blotch (confirmed by isolation to be caused by Bipolaris sorokiniana), was observed in May and at low to moderate severity and was rated on 19-May (Table 1, Figure 3). Leaf rust was noted on the upper canopy (flag leaf and F-1) after the rain in May, but it was at low levels that did not exceed 5% severity on the untreated check. Foliage senesced quickly after 19-May and no more ratings could be made. No indication of phytotoxicity by any fungicide treatment was observed.
Figure 1. Powdery mildew (PM) disease distributions (in %) in the plots before fungicide application.
Figure 2. Powdery mildew (PM) disease distributions (in %) in the plots 19 days after fungicide application.
Figure 3. Leaf spot (mainly spot blotch) disease distributions (in %) in the plots 19 days after fungicide application.
Table 1. Summary of foliar wheat disease management with fungicides in Stillwater, Oklahoma 2022.
| Fungicide; rate (oz/ac) 1 Date of fungicide application: 30-Apr Growth stage of application: 10.1 | Powdery Mildew (%) (before fungicide application) 2 | Powdery Mildew (%) (after fungicide application) 3 | Leaf Spot (%) (Mainly spot blotch) 4 |
| Dates of disease ratings | 19-Apr | 19-May | 19-May |
| ALB4010B @ 2 oz/A | 16.25 | 5.00 bcd | 3.75 bcd |
| ALB4010B @ 3 oz/A | 16.25 | 10.00 ab | 0.00 d |
| ALB4010B @ 4 oz/A | 22.50 | 8.75 bc | 5.00 bcd |
| ALB4024B @ 4 oz/A | 13.75 | 7.50 bcd | 3.75 bcd |
| ALB4024B @ 7 oz/A | 30.00 | 6.25 bcd | 3.75 bcd |
| ALB4024B @ 10 oz/A | 22.50 | 3.75 bcd | 2.50 cd |
| Propi-Star @ 2 oz/A | 17.50 | 1.25 d | 6.25 bc |
| Propi-Star @ 3 oz/A | 17.50 | 10.00 ab | 8.75 ab |
| Propi-Star @ 4 oz/A | 21.25 | 7.50 bcd | 5.00 bcd |
| Quilt Xcel @ 4 oz/A | 16.25 | 1.25 d | 3.75 bcd |
| Quilt Xcel @ 7 oz/A | 17.50 | 2.50 cd | 1.25 cd |
| Quilt Xcel @ 10 oz/A | 17.50 | 3.75 bcd | 1.25 cd |
| Untreated Check | 18.75 | 16.25 a | 12.50 a |
| LSD (p=0.05) | — | 7.24 | 5.88 |
1Plus 0.125% Induce (v/v) added to all treatments.
2Powdery mildew rated on leaves in lower canopy on 19-Apr
3Powdery mildew rated on leaves on flag leaves on 19-May
4Leaf spot rated on flag leaves on 19-May
SUMMARY: Results from this trial demonstrated the value of fungicide to manage foliar fungal diseases (powdery mildew and leaf spot). Fungicide application (growth stage 10.1; 30-April) managed powdery mildew and leaf spot development. For the four used fungicides, the rate did not have significant effect on the severity of powdery mildew and leaf spot.