With unpredictable rainfall patterns, increasing temperatures, and other weather-related factors, wheat disease pressure is likely to increase. When scouting fields, proper disease identification is critical for determination of a proper fungicide application.
Important wheat diseases to look out for when scouting
Oftentimes “lesions” or “spots” can look similar to many things and some non-yield limiting pathogens can produce symptomology and signs similar to yield-limiting pathogens. In the figures below we will discuss some of the major yield-limiting diseases encountered and how to properly manage each.What is Leaf Rust (Brown Rust)?
Leaf rust, also called brown rust, occurs across the U.S. and can cause severe yield loss in epidemic years. Leaf rust pustules rupture the leaf epidermis but lack tear marks. These pustules contain orange-brown, rusty colored spores. Pustules first develop on lower leaves and progress up the plant.
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Figure 1: Leaf rust on wheat
What are the symptoms of Leaf Rust?
Symptoms can be present from seedling stages through ripening. Leaf rust pustules are scattered, not in a linear pattern like stripe rust.
Why is Leaf Rust harmful?
Leaf rust causes the most damage when it is severe at heading, flowering or milk, and not as damaging at soft dough or later. If a fungicide is used, the application should be applied preventively and target the flag leaf (Feekes Growth Stage 8-9).
What Fungicides are recommended for Leaf Rust?
Implementing a single or dual mode of action (MOA) product containing a strobilurin and triazole such as Innliven™ or Innliven™ P can be effective at managing this disease.
What Fungicides are recommended for Leaf Rust?
Implementing a single or dual mode of action (MOA) product containing a strobilurin and triazole such as Innliven™ or Innliven™ P can be effective at managing this disease.
What is Stripe Rust?
Evidence of increased aggressiveness of stripe rust in the United States has been reported recently. Stripe rust has been more prevalent in the southern part of the U.S. and was the second ranked disease-causing yield loss in 2022.
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Figure 2: Stripe rust on wheat
What does Stripe Rust look like?
The first sign of stripe rust is the appearance of yellow streaks (pre-pustules), followed by small, bright yellow, elongated uredial pustules arranged in conspicuous rows on the leaves, leaf sheaths, glumes and awns (Figure 2). Mature pustules will break open and release yellow-orange masses of urediniospores. In some varieties, long, narrow yellow stripes will develop on leaves.How does Stripe Rust develop?
The pathogen is best sustained when nighttime temperatures are < 60 ºF. Infection and disease development is most rapid between 50–60 ºF. Urediniospores are spread via wind currents to healthy plants where they can initiate new infections. Heavy dew or intermittent rains can accelerate the spread of the disease. Infection tends to cease when temperatures consistently exceed 71–73 ºF.Treating Stripe Rust
Implementing a single or dual mode of action (MOA) product containing a strobilurin and triazole such as Innliven™ or Innliven™ P can be effective at managing this disease. If a fungicide is used, the application should be applied preventively and target the flag leaf (Feekes Growth Stage 8-9).What is Fusarium head blight (FHB)?
Fusarium head blight (FHB), also known as scab or head blight, is caused by Fusarium graminearum and other Fusarium spp. It reduces yield and produces mycotoxins that impact human and animal health. Infected spikelets are bleached and disease spreads upward and downward by sequentially infecting spikelets.
What does FHB look like?
Pink or orange spore masses can sometimes be observed on infected spikelets, particularly at the base. Warm, wet weather with high relative humidity during flowering (anthesis) and early grain formation favors disease development.
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When should treatment for FHB happen?
The best application timing is early flowering (FGS 10.51), but application up to 7 days after initiation of flowering can reduce FHB and mycotoxin contamination. Fungicides, primarily triazoles (FRAC group 3) and SDHI (FRAC group 7), are labeled for FHB.Do not use QoI (strobilurin; FRAC group 11) fungicides as these can increase mycotoxins. Harvest fields with FHB separately and avoid mixing contaminated and noncontaminated grain.
What do I need to look out for during the wheat growing season?
Be mindful of your surroundings and the adjacent fields around the wheat. There have been a lot of spring herbicide burndown applications and some pre-emergence applications made that could result in off-target movement producing symptoms similar to diseases.
Additionally, keep an eye on the weather. The environment will dictate the severity of a disease and how it will progress over time. Fungicide applications utilizing dual modes of action with the addition of an adjuvant and high spray volumes are recommended.
The Takeaway
For further information or help making in-field diagnosis, please consult any of your local Agronomic Sales Enablement Team members or your local Simplot Grower Solutions Crop Advisor.Authors
Connor Ferguson, Texoma
Ben Lawrence, Bayou
Jeffrey Mansour, Midsouth
Justin McCoy, Southwest
