Leaf Spot Fungicide
2013 – 2015
Diseases [leaf spots, rusts and fusarium head blight (FHB)] have greatly reduced wheat yield and quality in western Canada in recent years. Wheat growers want to know the level of leaf spot control that can be expected with a fungicide application at the heading stage (FHB timing) of wheat, or in other words if a single fungicide application aimed at control of FHB will also provide effective leaf spot control. This proposed project aims to answer this question. Normally, fungicides are applied at the seedling stage and/or at flag leaf emergence for control of leaf spot diseases and at head emergence (to early anthesis) for FHB, but there is very little information on the potential benefits of fungicide applied at the FHB timing (early anthesis) for leaf spot control. In addition to conventional fungicides, new tools to manage FHB, e.g. biofungicides have been shown to reduce FHB symptoms and DON accumulation in durum wheat.
This project will determine the efficacy of conventional fungicides and a biofungicide, to manage fusarium head blight and leaf spotting diseases. The results will be used to develop effective fungicide strategies for wheat growers. We propose to evaluate the effect of fungicide applications for fungal leaf and head diseases of wheat at two application timings (flag emergence and early anthesis) when applied singly or in tank-mix pairs. We also plan to evaluate a biofungicide that claims to have efficacy against FHB.
Location: Lethbridge, Brooks, Lacombe, Saskatoon, Indian Head and Melfort
We grew the Canada Western Spring wheat variety ‘Carberry’ because it’s moderately susceptible to leaf spotting but resistant to RHB. Applications of fungicide consisted of a single application at flag-leaf stage, a single application during anthesis, and a dual application at both stages.
- prothioconazole + tebuconazole (Prosaro at 800 mL ha-1 )
- tebuconazole (Folicur 250 EW at 499 mL ha-1 140 , or at Lacombe, 2014, Folicur 432 F at 291 mL ha-1
- subtilis (Serenade Optimum 500 g ha-1 141 )
All treatments were applied in 100 L ha-1 142 of water.
Disease severity was determined by assessing ten flag leaves and ten penultimate leaves from each plot using the Horsfall–Barratt scale. This is a scale of 1 -11. Ratings were then converted to percent leaf area is affected by disease.
Fifty random spikes were assessed from each plot through the early stages of development for FHB severity.
The data collected from each site-year were classified into high disease locations, where leaf-spot disease severity was 40 per cent or greater in unsprayed checks, and low disease locations, where disease severity was less than 40 per cent. Each classification was analyzed separately.
High Disease Locations – Saskatoon, Melfort and Lacombe
The average leaf-spot disease severity of the unsprayed check was 73.2 per cent.
Differences in disease severity:
- Anthesis application– 41 per cent
- Flag-leaf application – 34.7 per cent
- Dual application – 20.2 per cent
Synthetic fungicides reduced leaf-spot disease severity compared to the untreated control. Biological fungicide (B. subtilis) did not. Tebuconazole reduced the severity to 36.1 per cent. Prothioconazole and tebuconazole reduced it to 27.6 per cent. There were no differences in FHB among fungicide treatments.
Low Disease Locations – Lethbridge, Brooks, Saskatoon, and Indian Head
The average disease severity of the unsprayed check was 16.2 per cent which was reduced to 6.6 per cent with the application of fungicide.
Differences in disease severity:
- Anthesis application – 7.6 per cent
- Flag-leaf application – 7.1 per cent
- Dual application – 5 per cent
Differences in leaf disease severity between flag-leaf and anthesis stage fungicide were only detected at high disease locations. They were also observed when fungicide was applied at flag-leaf or anthesis timings compared to the dual application treatment under both high and low disease severity situations. The study determines the best time to apply fungicide was between the flag leaf and medium milk growth stages.
Our results indicate there was no yield penalty when applying fungicide at the anthesis stage under high disease scenarios. However, there was no yield benefit to fungicide application when the level of leaf diseases are low. Disease severity was lower when fungicide was applied at flag leaf stage as opposed to anthesis. A single fungicide application at anthesis, in comparison to the flag-leaf stage, will give producers control over leaf spotting activity, maintain their yield and improve grain quality.