Foliar Wheat Disease Management with Xyway Fungicide – Oklahoma 2024

Categories: Fungicides

Meriem Aoun, Small Grains Pathologist

Department of Entomology & Plant Pathology Oklahoma State University

COOPERATORS: Dr. Meriem Aoun¹, Brian Olson¹, Tyler Pierson², and Dr. Amanda de Silva Oliveira²

¹Departments of Entomology & Plant Pathology, Oklahoma State University, Stillwater, OK; ²Plant & Soil Science, 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:  10-NOV-2023 at 90 lb/ac

FUNGICIDE APPLICATION DATES:

Dribble application over top of row and impregnated Fert GR: 10- NOV-2023

Flag leaf application @ Feekes’ growth stage 10.1 (GS 10.1: heads (awns) just starting to emerge from the boot): 19-APR-2024.

TARGET ORGANISMS (DISEASES): P. striiformis (stripe rust), Puccinia triticina (wheat leaf rust), Blumaria graminis f. sp. tritici (wheat powdery mildew), and 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, 150 lbs/ac of 46-0-0 (Urea) and 150 lbs/ac 18-46-0 (Diammonium Phosphate/DAP) dry fertilizer were applied on September 9, 2023. On Feb 7, 2024, a top dress with 50 lbs/ac of 46-0-0 (Urea) was applied.

Herbicide:  None applied

Insecticide:  Gaucho 600 (2.4 fl oz/cwt) applied as a seed treatment to limit barley yellow dwarf

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 15 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. The grain yield of the plots was adjusted to 12% moisture.

GENERAL OBSERVATIONS: 

Fall and winter rains (accumulated rainfall OCT-FEB was 10.9 inches) in Stillwater provided adequate moisture for good wheat growth and development. The accumulated rainfall in spring of 2023 (March – May) was 11.6 inches with the highest levels of moisture recorded in May 2024 (7.5 inch). By early April, the wheat was ahead of schedule, with the flag leaf appearing around two weeks earlier than normal. Low levels of barley yellow dwarf (BYD) infections were present but scattered randomly across the trial. Although BYD may have slightly impacted yield it was not a major concern. 

Stripe rust was the most prevalent disease in April and May and was early and severe. Stripe rust was first observed on March 31 in this trial. On April 19, stripe rust severity reached 49% on average on the untreated check. The stripe rust severity in the Xyway trial was rated on April 19, which was just before the flag leaf application of Adastrio (in treatments # 6 and 11). Leaf rust was also severe around the last week of April – early May. As leaf rust and stripe rust co-occurred in the Xyway trial at high levels, stay green ratings were collected on May 1 and May 9, 2024. Foliage senesced quickly after May 9 and no more ratings could be made. No indication of phytotoxicity by any fungicide treatment was observed. The rainfall in May delayed harvest by a couple of weeks. The plots were harvested on June 19, 2024.

SUMMARY: 

Results from this trial demonstrated the efficacy of some fungicide applications to manage foliar fungal diseases (stripe rust and leaf rust) (Table1). The average stripe rust severity on the untreated check reached 49% on April 19. The average stay green on the untreated check was 30% and 2.5% on May 1 and May 9, respectively. Stay green ratings accounted for both leaf rust and stripe rust infections. Yield (adjusted to 12% moisture) ranged from 22.9 bu/ac to 83.2 bu/ac. Test weight ranged from 49.0 to 59.9 lb/bu. For the untreated check, yield was 22.9 bu/ac and test weight was 50.2 lb/bu.

The most effective fungicide treatments in this trial were treatment #6 (Xyway LFR 8.9 + 10-34-0 @ 6 gallons/A dribble over top of row fb Adastrio 8 oz/ac + 0.25% v/v NIS @ flag leaf) and treatment #11 (Xyway LFR (8.9 fl oz) Impregnated Fert GR (11-52-0) 50 lbs/A in-furrow @ planting fb Adastrio 8 oz/ac + 0.25% v/v NIS @ flag leaf). There was a significant disease control and yield benefit by applying Adastrio 8 fl oz/ac at flag leaf stage. Treatments #9, 10, 4, and 5 (table 1) also performed better compared to the untreated check. Xyway LFR impregnated Fert GR or dripple application at a rate ≥ 8.9 fl oz significantly reduced rust diseases and consequently increased yield compared to the untreated check.

Table 1.  Summary of foliar wheat disease management in the Xyway fungicide trial at Stillwater, Oklahoma 2024.