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Corn Scouting Calendar

 

Corn Scouting Calendar

The corn scouting calendar provides tips for identifying corn pests and insects as well as management considerations when scouting fields.* Additional information for most pests is available by clicking on the pest name.

Insect / DiseaseGrowing StageSymptoms
Seedcorn Maggot VE through V1+
  • Seedcorn maggots damage corn by feeding inside the kernel, resulting in failed germination or emergence of a weakened seedling. Any condition that delays germination results in more exposure of the seed to attack. Cold, wet soils are therefore more likely to result in injury.
Seedcorn Beetle VE through V1+
  • Damage to corn seeds is more likely in cool, wet springs when the seeds are slow to germinate but the insects are still actively feeding.
  • No-till fields are less likely to have damage.
Wireworm VE through V3
  • In most cases, wireworms are spring pests only as they move deeper and may aestivate as soils warm during the summer.
  • Hosts: any fibrous rooted plant species, including corn, pasture, small grains and other grasses.
  • Larvae are opportunistic; unable to move more than a few inches, they must feed on what is present.
Black Cutworm VE through V3+
  • 4th stage or older larvae exceed the width of a dime in length and can begin cutting V1-V5 stage plants.
  • Drilling into V6-V8 stage plants can kill growing point.
White Grub VE through V3+
  • Damage only occurs on the young corn seedling.
  • Significant damage can occur from true white grub densities of one larva per cubic foot prior to planting.
Corn Flea Beetle VE through V3+  
Armyworm V1 through V3+

 

Hop Vine Borer V1 through V3
  • Adult: dull brown moth with buff-colored front forewings and dull-white hind wings; wingspan 1½ inches.
  • Larva: solid orange or reddish-brown head with black eyes; large dark purple or brown spots, almost square-shaped, along the back with transverse rows along the side, and separated by contrasting dirty white lines.
Stewart's Leaf Blight V1 through VT
  • Occur soon after plant emergence.
  • Yellowed or bleached leaf streaks.
Billbug V1+ through V3  
Grape Colaspis V1+ through V3+
  • Grape colaspis larvae feed on root hairs and may eat narrow strips from the roots. Stripped roots cannot obtain moisture and nutrients efficiently.
Brown Stinkbug V1+ through V3+
  • Stinkbugs feed with piercing and sucking mouthparts, similarly to mosquitoes. Mouthparts pierce the surface, inject an enzyme, then re-ingest the dissolved plant material.
  • Stink bugs feed on growing plants and may cause misshapen or stunted plants that grow improperly.
Common Stalk Borer V1 through V6  
Corn Rootworm Larvae V1+ through VT
  • WCR and NCR are found throughout the western and northern Corn Belt - MCR is locally important in the West only, and SCR can be found throughout the U.S. but rarely causes economic damage.
  • More prevalent in fields following corn.
Goss's Wilt V1 through R5
  • Disease is caused by a bacterial pathogen that overwinters in residue of corn and several grasses.
  • Depending on conditions, may cause only minor problems or devastating damage with grain yield losses approaching 50%.
European Corn Borer V6+ through R6
  • One larva per plant tunneling in stalk may reduce yield by up to:5-8% pre-tassel, 2-5% post-tassel.
Common Rust V6+ through R1
  • Favored by moist, cool conditions (temps in the 60s and 70s).
  • Hot, dry conditions typically slow or stop development.
Fall Armyworm V6+ through R1
  • Does not overwinter in most of the Corn Belt but moves north during the season on storms.
  • Favorable conditions: Semi-tropical and tropical climates, Late-planted corn in whorl stage.
Gray Leaf Spot V6+ through R3
  • Typical lesions of gray leaf spot are rectangular with straight edges.
  • Lesion expansion is limited by parallel leaf veins.
  • Lesion appearance may differ somewhat on different genetic backgrounds.
Northern Leaf Blight V6+ through R3
  • Survives in corn debris and builds up over time in high-residue and continuous corn cropping systems.
  • Favored by heavy dews, frequent showers, high humidity and moderate temperatures.
  • Spores are spread by rain splash and air currents to the leaves of new crop plants in spring and early summer. Spores may be carried long distances by the wind.
Southwestern Corn Borer V6+ through R6
  • Adult: dull-white or buff-colored moth; wingspan 3/4 to 1 1/2 inches (19 to 38 mm).
  • Larva: (summer phase) creamy white with large, raised brown or black tubercles on each body segment; (winter phase) creamy white and without distinctive spots; head black (instars 1 to 3) or reddish brown (instars 4 to 6).
Corn Leaf Aphids V6+ through R1
  • Can cause yield loss by feeding and causing stress on the plant but also is an important vector of corn viral diseases such as maize dwarf mosaic in corn and barley yellow virus in wheat.
Corn Rootworm Adults V9+ through R1
  • Most damaging corn pest, considered to cause more than $1 billion annual loss in North America.
  • More prevalent in fields following corn.
Japanese Beetle V9+ through R4
  • Most damage is from adult feeding; however, the larval grub also can feed on roots.
  • Late-planted fields are at greater risk.
  • Japanese beetles are often found in field edges or areas of delayed growth.
Fusarium Stalk Rot V9+ through R4
  • Overwinters as mycelia in infected crop debris, spread by wind and rain splash.
  • Can infect the plant directly through the roots, causing root and lower stalk rot.
  • Favored by warm, relatively dry weather; plant stress following pollination; and other diseases.
  • Disease generally progresses during reproductive stages of corn development.
Gibberella Stalk Rot V9+ through R4
  • Overwinters in infected crop residue of corn or other cereals.
  • Insect injury often allows pathogen to enter the plant.
  • Can infect corn at the leaf sheaths, brace roots or roots. Infection continues from roots into lower stem.
Charcoal Rot V9+ through R1
  • Charcoal rot begins as a root infection, which spreads into the lower stalk internodes and causes early ripening, shredding and breaking at the crown of the corn stalk.
  • Charcoal rot survives in soil or corn residue as sclerotia, which are round, small black structures that overwinters on corn residues.
  • Favored by warm, relatively dry weather; plant stress following pollination; and other diseases.
Western Bean Cutworm R1 through R4
  • Major larval feeding coincides with the ear development.
  • Direct feeding on the ears reduces grain yield.
  • Infestations of several larvae per ear can reduce grain yield up to 40%.
Corn Earworm R1 through R4
  • Grain losses estimated at 2.5% annually.
  • Losses in southeastern U.S. as high as 16.7%.
  • Losses in sweet corn as high as 50% in unsalable produce.
  • Found worldwide but does not usually overwinter in most of the Corn Belt and must re-infest each year.
Anthracnose Stalk Rot R2 through R6
  • Most common stalk disease of corn.
  • Favored by plant stress following pollination.
  • Disease development may result in: Plant lodging, Reduced ability to harvest, Yield reduction.
Diplodia Ear Rot R2 through R6
  • Wet weather during grain fill and upright ears with tight husks promote Diplodia.
  • Can cause ear rot, stalk rot and seedling blight.
  • Diplodia is highly dependent on quantity of infected, unburied corn residue (stalks, cobs and kernels).
Fusarium Ear Rot R3 through R6
  • Disease enters ear primarily through wounds from hail or insect feeding.
  • Insects damage husks and kernels and may also vector Fusarium spores.
  • Ear rot severity is usually related to severity of European corn borer, western bean cutworm or corn earworm feeding damage.
  • Airborne spores can germinate and grow down the silk channel to infect kernels.
Gibberella Ear Rot R3 through R6
  • Overwinters in infected crop residue.
  • Spores are spread from crop residue to corn ears by wind and rain splash.
  • Infection of corn ears occurs through young silk.
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