Skip directly to: content | section navigation | search

more options
Skip Navigation LinksField Crops > Corn > Managing Corn Diseases
Managing Corn Diseases 

 

Diseases of Corn

Management of Corn Diseases

Anthracnose Leaf Blight
Anthracnose Stalk Rot
Common Rust
Common Smut
Eyespot
Gray Leaf Spot
Northern Corn Leaf Blight
Northern Leaf Spot
Stewart's Bacterial Leaf Blight

Fungicides for Corn Disease Control in New York State

Conducting On-Farm Corn Foliar Fungicide Strip Trials

 

 

Diseases of Corn

Anthracnose Leaf Blight

Disease Facts
Anthracnose leaf blight of corn caused by the fungus Colletotrichum graminicola is an economically important foliar disease of corn in New York State especially in no-till or reduced till fields.

The fungus overwinters on corn debris producing spores that infect the next year’s crop. Mild, wet conditions favor disease as spores are spread through rain splashing.

Anthracnose leaf blight occurs early in the growing season affecting lower leaves initially with late season disease progression affecting the upper leaves.

Management Strategies
Use of resistant hybrids is the most effective control method available.

Since the fungus overwinters in crop residue, no-till or reduced-till practices can lead to an increase in disease when corn follows corn.

In cases where no-till or reduced-till practices are used, crop rotations for two to three years in conjunction with resistant hybrids would be an effective control strategy.

 

 

Symptoms
Early season symptoms appear as small, oval to elongate water soaked lesions on lower leaves. These semitransparent spots gradually enlarge to ¾ inch long and become tan at the center with red to reddish-brown or yellow-orange borders.

The entire leaf may become blighted as the lesions coalesce and severely blighted leaves will yellow and die.

During periods of wet weather, fungal fruiting bodies appearing as black specks may be found within the center of the lesions.

In late season, symptoms may appear on upper leaves.

Top of Page

Anthracnose Stalk Rot

Disease Facts
Also caused by the fungus Colletotrichum graminicola, Anthracnose stalk rot of corn can lead to reduced ear development.

Conditions favoring this disease include warm humid weather especially when corn follows corn.

Rain splashing can carry spores from blighted leaves and corn debris. The fungus overwinters on leaf and stalk debris serving as a source of disease in upcoming growing seasons.

Infection is more severe when there is injury from European corn borer.

Management Strategies
Since spores can overwinter in crop debris, reducing crop residues with tillage and crop rotation can help to manage this disease.

Additionally, management can be achieved by using hybrids that have resistance to both the leaf and stalk rot phase of anthracnose as well as the use of Corn borer-resistant (Bt) hybrids.

Symptoms
Symptoms of anthracnose stalk rot are usually observed later in the season after tasseling.

Symptoms on the stalk consist of tan to reddish brown watersoaked lesions in the rind.

These lesions coalesce and enlarge turning dark brown to shiny black. This is accompanied by a brown to black discoloration of the pith.

Typically the rot is below the ear and may cause severe lodging.

 

Top of Page
 

Common Rust

Disease Facts
Common rust is caused by the fungus Puccinia sorghi. Late occurring infections have limited impact on yield.

The fungus overwinters on plants in southern states and airborne spores are wind-blown to northern states during the growing season.

Disease development is favored by cool, moist weather (60 – 70 F).

Management Strategies
The use of resistant hybrids is the primary management strategy for the control of common rust.

Timely planting of corn early during the growing season may help to avoid high inoculum levels or environmental conditions that would promote disease development.

 

Symptoms
Symptoms of common rust often appear after silking.

Small, round to elongate brown pustules form on both leaf surfaces and other above ground parts of the plant.

As the pustules mature they become brown to black.

If disease is severe, the leaves may yellow and die early.

 

Top of Page

Common Smut

Disease Facts
Common smut caused by the fungus Ustilago maydis is a common disease of field corn found in New York State.  

Common smut may infect all above ground parts of the plant but causes the greatest economic losses when the ear becomes infected or if smut galls form on the stalks immediately above the ears.

Infection is favored by dry conditions as seen during a drought as well as mechanical injury due to hail.

Higher levels of common smut are observed in fields with soils with high N levels or after heavy applications of manure.

Management Strategies
Management strategies include the use of resistant hybrids and avoiding mechanical injury of plants.

Proper maintenance of soil fertility can also play a role in managing this disease.

Symptoms
White, soft galls may form on all above ground parts of the plant including ears, tassels and leaves.

As the galls age, the interior darkens turning into masses of dark green to black powdery spores.

Top of Page

Eyespot

Disease Facts
Eyespot, caused by the fungus Kabatiella zeae, is common and can be found across New York State.

Eyespot is favored by cool, wet weather. Spores are spread long distance by wind and locally by rain splashing from crop debris in soil onto host plants.

Management Strategies
This disease is rarely a target for foliar fungicides.

Management strategies include the use of resistant hybrids.

Disease management can also be aided by minimizing crop residue through clean plowing and implementing crop rotations in fields where disease has occurred.

Symptoms
Eyespot presents as many circular to oval spots on the leaf which may coalesce to form large areas of dead tissue.

Initially spots appear water-soaked eventually forming tan to cream colored centers surrounded by brownish purple margins with a narrow yellow halo.

The haloed spots give the appearance of an “eyespot.”

Top of Page

Gray Leaf Spot

Disease Facts
Gray leaf spot is caused by the fungus Cercospora zeae-maydis.

Epidemics of gray leaf spot have been observed in New York State in the Southern Tier and the Hudson River Valley. New hot spots of the disease have been reported in the Mohawk Valley and the Leatherstocking Region.

Gray leaf spot is favored by wet humid weather as often found in valley microclimates. Additionally, it is favoved in situations with reduced tillage and continuous corn.

Airborne spores are spread locally and regionally from corn debris.

Management Strategies
Management strategies for gray leaf spot include tillage, crop rotation and planting resistant hybrids.

Fungicides may be needed to prevent significant loss when plants are infected early and environmental conditions favor disease.

 
 

Symptoms
Symptoms of gray leaf spot are usually first noticed in the lower leaves.

Initially, lesions of gray leaf spot begin as a small dot with a yellow halo.

Lesions will elongate over time running parallel to the veins becoming pale brown to gray and rectangular in shape with blunt ends. These lesions can be described as having the appearance of a “matchstick.”

Lesions may eventually coalesce killing the leaves.

Leaves appear grayish in color due to the presence of fungal spores.

Top of Page

Northern Corn Leaf Blight

Disease Facts
Northern corn leaf blight caused by the fungus Exerohilum turcicum is a common leaf blight found in New York.

If lesions begin early (before silking), crop loss can result. Late infections may have less of an impact on yield.

Northern corn leaf blight is favored by wet humid cool weather typically found later in the growing season.

Spores of the fungus that causes this disease can be transported by wind long distances from infected fields. Spread within and between fields locally also relies on wind blown spores.

Management Strategies
Northern corn leaf blight can be managed through the use of resistant hybrids.

Additionally, timely planting can be useful for avoiding conditions that favor the disease.

 

 

Symptoms
The tan lesions of northern corn leaf blight are slender and oblong tapering at the ends ranging in size between 1 to 6 inches.

Lesions run parallel to the leaf margins beginning on the lower leaves and moving up the plant. They may coalesce and cover the enter leaf.

Spores are produced on the underside of the leaf below the lesions giving the appearance of a dusty green fuzz.

Top of Page

Northern Corn Leaf Spot

Disease Facts
Northern corn leaf spot caused by the fungus Cochliobolus carbonum has become more prevelant with the greater use of no-till systems.

Although there are several races of the fungus that cause disease, Race 3 most likely causes the greatest impact in New York State.

Northern corn leaf spot is favored by high humidity and warm weather.

Spores can overwinter in crop residue serving as inoculum for subsequent crops.

Airborne spores can be transported long distances from infected fields.

Management Strategies
In addition to crop rotations and tillage, the use of resistant hybrids is the most effective control for northern corn leaf spot.

Symptoms
Symptoms of northern corn leaf spot usually appear at the time of silking or at full maturity.

Symptoms of northern leaf spot consist of circular tan to brown lesions (1/8 to ½ inch) running in a line along the leaf vein. These lesions are often descibed as looking like a "string of pearls."

 

Top of Page

Stewart's Bacterial Leaf Blight

Disease Facts
Stewart’s Bacterial Leaf Blight is caused by the bacterium Pantoea stewartii.

This disease is transmitted to corn by corn flea beetles. Flea beetles carry the bacterium and introduce it into the corn when feeding.

Disease occurrence and severity can be predicting based on the temperature of the preceding winter. Warmer winters can favor increased survival and higher poepulations of flea beetles leading to increased severity of Stewart’s Bacterial Leaf Blight during the following growing season.

Management Strategies
The use of resistant hybrids is the key management strategy for Stewart’s bacterial leaf blight.

 
 

Symptoms
Young plants when infected most often wilt and die due to systemic infection.

Leaf blight associated with this disease occurs later in the growing season usually after tasseling.

Leaf blight leasions are long and linear with wavy margins (> 1 inch). These lesions will start in the upper part of the plant unlike most foliar diseases that start at the bottom of the plant.

Flea beetle feeding may be evident in the lesions.

Top of Page

Management of Corn Diseases in New York

Table 1. Fungicide Efficacy for Control of Corn Diseases (July 2013) (click on table to enlarge)

 This information was adapted for New York by Gary C. Bergstrom, Cornell University, from information developed by the Corn Disease Working Group (CDWG) on fungicide efficacy for control of major corn diseases in the United States.  Efficacy ratings for each fungicide listed in the table were determined by field testing the materials over multiple years and locations by the members of the committee. Efficacy ratings are based upon level of disease control achieved by product, and are not necessarily reflective of yield increases obtained from product application. Efficacy depends upon proper application timing, rate, and application method to achieve optimum effectiveness of the fungicide as determined by labeled instructions and overall level of disease in the field at the time of application. Differences in efficacy among fungicide products were determined by direct comparisons among products in field tests and are based on a single application of the labeled rate as listed in the table.  Table includes systemic fungicides available that have been tested over multiple years and locations. The table is not intended to be a list of all labeled products1. Efficacy categories: NR=Not Recommended; P=Poor; F=Fair; G=Good; VG=Very Good; E=Excellent; NL = Not Labeled for use against this disease; -- = Insufficient data to make statement about efficacy of this product for this disease.

1Additional fungicides are labeled for disease on corn, including contact fungicides such as chlorothalonil. Certain fungicides may be available for diseases not listed in the table.

2Harvest restrictions are listed for field corn harvested for grain.  Restrictions may vary for other types of corn (sweet, seed or popcorn, etc.), and corn for other uses such as forage or fodder.

3Aerial application in New York is allowed except within 100 feet of an aquatic habitat.

4Aerial application is not allowed in New York.

Many products have specific use restrictions about the amount of active ingredient that can be applied within a period of time or the amount of sequential applications that can occur.  Please read and follow all specific use restrictions prior to fungicide use.  This information is provided only as a guide.  It is the responsibility of the pesticide applicator by law to read and follow all current label directions.  Reference to products in this publication is not intended to be an endorsement to the exclusion of others that may be similar. Persons using such products assume responsibility for their use in accordance with current directions of the manufacturer. Members or participants in the CDWG assume no liability resulting from the use of these products.

Related Resources:
Foliar Fungicides for Corn in New York State Presentation - PDF

Top of Page

On-Farm Corn Foliar Fungicide Strip Trials

Local growing conditions, disease pressures and cropping practices can all impact the effectiveness and economic worth of foliar fungicides of corn. For this reason, it can be very useful for growers to conduct fungicide strip trials to determine the added value of foliar fungicides on their own fields. Below are documents that provide useful informaton on how to conduct a fungicide strip trial at flowering stages including data collection and disease assessment information.

Conducting On-Farm Corn Foliar Fungicide Strip Trials - PDF

Collecting Data for On-Farm Corn Foliar Fungicide Strip Trials - PDF

Top of Page

Information on this page updated 09/2012