Disease Guide
University-rated fungicide efficacy, pricing per acre, and spray timing for common rust (Puccinia sorghi). Based on Crop Protection Network 2025 data.
Common rust is a foliar disease of corn caused by the obligate pathogen Puccinia sorghi. It is one of the most frequently observed corn leaf diseases across the U.S. Corn Belt, though it is typically the least economically damaging of the major foliar diseases. The pathogen produces elongated, cinnamon-brown to reddish-brown pustules (uredinia) on both upper and lower leaf surfaces.
Like southern rust, common rust does not overwinter in the Corn Belt — spores blow northward from tropical and subtropical regions each season. The disease favors cool to moderate temperatures (60-75°F) and high humidity, which distinguishes it from southern rust's preference for warmer conditions. Common rust infections typically peak during cool, wet spells in June and July, and often slow or stop as temperatures rise above 80°F.
Yield losses from common rust are typically minor — 2-8% in most situations. Modern corn hybrids carry partial resistance genes that limit the disease's severity. Standalone fungicide applications targeting only common rust are rarely economical. However, common rust is easily controlled as a secondary benefit of fungicide applications made for higher-priority diseases like tar spot, gray leaf spot, or northern corn leaf blight.
Efficacy ratings from the Crop Protection Network 2025, based on multi-year university field trial data. Only products with tested ratings are shown — untested or not-listed products are excluded.
| Product | Mode of Action | Common Rust Rating |
|---|
Source: Crop Protection Network 2025. Ratings reflect multi-year, multi-location field trial performance.
Efficacy ratings cross-referenced with real purchase prices. Products sorted by efficacy rating — best performers first.
| Product | Common Rust Rating | Best $/Acre |
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Prices as of early 2025 from AgChem, FBN, and Farmerceag. Actual pricing varies by geography, volume, and timing.
Standalone treatment is rarely needed. Common rust in modern corn hybrids almost never warrants a fungicide application on its own. The disease is self-limiting — it slows dramatically when temperatures exceed 80°F, and most hybrids carry enough genetic resistance to prevent economically significant damage.
Incidental control from other applications. If you're already applying fungicide at VT-R1 for tar spot, gray leaf spot, or NCLB, you'll get excellent common rust control as a bonus. Nearly all modern fungicides rate Very Good or Excellent for common rust.
When to consider treating for common rust specifically. Fungicide may be justified for common rust alone in three situations: (1) seed corn production fields where even minor disease reduces seed quality, (2) sweet corn where cosmetic ear quality matters, or (3) fields with highly susceptible hybrids during extended cool, wet periods where pustule density is extremely heavy before tasseling.
Don't confuse with southern rust. If you see rust pustules in warm weather (July-August, above 80°F), look closely — it may be southern rust, which is far more damaging and does require immediate treatment. Common rust pustules are larger, more elongated, and on both leaf surfaces. Southern rust pustules are small, circular, and primarily on the upper surface.
Efficacy ratings for all 26 products across 7 diseases, pricing from 3 suppliers, decision frameworks, and an ROI calculator.
View full guide →Search and filter 9,196 yield records from 867 university field trials by year, state, and crop.
Browse data →Fungicide ratings, pricing, and timing for tar spot (Phyllachora maydis).
View guide →Fungicide ratings, pricing, and timing for gray leaf spot (Cercospora zeae-maydis).
View guide →Fungicide ratings, pricing, and timing for NCLB (Exserohilum turcicum).
View guide →Fungicide ratings, pricing, and timing for southern rust (Puccinia polysora).
View guide →Fungicide ratings, pricing, and timing for anthracnose (Colletotrichum graminicola).
View guide →Fungicide ratings, pricing, and timing for eyespot (Aureobasidium zeae).
View guide →Based on Crop Protection Network 2025 data, multiple products rate Excellent for common rust, including Quadris, Headline, Delaro 325, Headline AMP, and Stratego YLD. Common rust is highly responsive to fungicide treatment — nearly all strobilurin and premix products provide Very Good or better control.
Common rust (Puccinia sorghi) and southern rust (Puccinia polysora) look similar but differ in key ways. Common rust pustules are larger, more elongated, and appear on both upper and lower leaf surfaces. Southern rust pustules are smaller, more circular, and primarily on the upper surface. Common rust favors cooler temps (60-75°F) while southern rust favors warm temps (80°F+). Common rust rarely causes significant yield loss in modern hybrids, while southern rust can be devastating.
In most cases, no. Common rust is typically a minor disease that rarely causes economically significant yield loss in modern corn hybrids with adequate genetic resistance. Fungicide is usually only justified for common rust when: (1) very susceptible hybrids are planted, (2) conditions are unusually cool and wet for extended periods, or (3) the field is a seed corn production field where even minor disease matters. Most common rust control comes incidentally from fungicide applications targeting other diseases.
Common rust pustules typically appear in the mid-vegetative stages (V8-V12) when cool, humid conditions favor the pathogen. Spores blow in from southern regions each year — the disease does not overwinter in the Corn Belt. Infections are most common during cool spells in June and July. By tasseling, most modern hybrids have developed sufficient resistance, and the disease stops progressing in warm weather.
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