Foliar Wheat Disease Management with Fungicides – 2022

Categories: Fungicides

COOPERATORS: Dr. Meriem Aoun¹, Dr. Amanda de Silva Oliveira², Brian Olson¹, & Tyler Pierson³

Departments of Entomology & Plant Pathology¹, Plant & Soil Science², and Field Research Services Unit³; 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’ hard red winter wheat              

SOIL TYPE:  Norge loam

PLANTING DATE & RATE:  15-Oct-2021 at 90 lb/ac

FUNGICIDE APPLICATION DATE(S):

16-Mar-2022 @ Feekes’ growth stage 6 (GS6: 1^st node detectable at base of main tiller)

30-Apr-2022 @ Feekes’ growth stage 10.1 (GS 10.1: heads (awns) just starting to emerge from the boot)

TARGET ORGANISMS (DISEASES): Blumaria graminis f. sp. tritici (wheat powdery mildew), Puccinia triticina (wheat leaf rust), and P. striiformis (stripe rust), Zymoseptoria tritici (Septoria leaf blotch)

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) test was conducted only if ‘F’ test was significant.

CULTURAL PRACTICES:

Fertilizer: Based on a soil test with a 50 bu/ac yield goal, 26 lb/acre of nitrogen, 107 lb/acre of phosphorus, and 233 lb/acre of Potassium were applied.

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, we took the percentage of leaf surface area covered by a disease.

HARVEST METHOD:  Plots were harvested with a Wintersteiger Delta small plot combine. Grain weight, test weight, and moisture content were collected from each plot. Grain moisture at harvest was ~ 8% for all plots. Grain yield of the plots was adjusted to 12% moisture.

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 at GS 10.1) and on 15-May (after fungicide application at GS 10.1). Leaf rust was noted on the upper canopy (flag leaf and F-1) after the rain in May, but it was late during the season and at low levels that did not exceed 5% severity on the nontreated check. Foliage senesced quickly after 15-May and no more ratings could be made. No indication of phytotoxicity by any fungicide treatment was observed.

SUMMARY: 

Results from this trial demonstrated the efficacy of most fungicide treatments to manage foliar fungal diseases (powdery mildew) (Table1).  The average powdery mildew severity of the nontreated check reached 33% on April 19 (rating on the lower and mid canopy) and 25% on May 15 (on the upper canopy; flag leaf and F-1). Yield (adjusted to 12% moisture) ranged from 50.51 bu/ac to 69.72 bu/ac. Test weight ranged from 59.0 to 60.35 lb/bu. For the nontreated check, yield was 58.20 bu/acre whereas test weight was 59.6 lb/bu.

Most early season fungicide treatments (GS 6; on 16-March) did not manage early season powdery mildew (rated on 19-April) to sufficient levels compared with the nontreated check. Compared to the nontreated check, yield was significantly higher for four treatments (i.e., Topguard fb Topguard, Topguard  fb Topguard EQ, ALB4010B (2.8 fl oz/a) and ALB4010B (4 fl oz/a). For these treatments, powdery mildew severity (15 days after application at GS 10.1) ranged from 8 to 15% (significantly lower than the nontreated check).

Table 1.  Summary of foliar wheat disease management with fungicides in Stillwater, Oklahoma 2022.

¹fb=followed by.

²GS (growth stage) is reported according to Feekes’ scale, where GS 6=first node detectable at base of main tiller;

  GS 10.1=heads just starting to emerge from boot with only awns visible.

³Powdery mildew rated on leaves in lower canopy on 19-Apr (before application at GS 10.1).

⁴Powdery mildew rated on leaves on flag leaves on 15-May (After application at GS 10.1).

⁵Yield values adjusted to 12% moisture.