Above-ground Pests of Corn

Corn Flea Beetle

• Order: Coleoptera (Family Chrysomelidae)

• Chaetocnema pulicaria

• Origin: Native to Western Hemisphere

• Distribution: Eastern United States

• Description: Small (<2mm long), shiny black elytra, enlarged femurs on hindlegs.

Corn Flea Beetle Life History

• Overwinter as adults at bases of grass adjacent to a cornfield

• Spring emergence. Early feeding is often on a secondary host

• Mated females eggs in soil near corn roots

• Larvae develop in soil. Pupation occurs in 14 days.

Corn Flea Beetle Life History

• Adults feed and mate during the rest of the summer

• During feeding, many beetles pick up and vector the bacteria, Erwinia stewarti by feeding on infected hosts. This bacteria leads to bacterial wilt.

Corn Flea Beetle Damage

• Bacterial Wilt: leads to stunted growth of seedling and wilt. Recognized by linear lesions and leaves with wavy edges.

• Damage to plants by feeding on the epidermis (generally not too damaging). This can be recognized by seeing windows within the plant tissue

Corn Flea Beetle Damage

Corn Flea Beetle Management

• Cold winters often result in a smaller adult population in Spring.

• Best cultural practice is to use resistant varieties of corn when available. These are often labeled BWR = Bacterial Wilt Resistant.

• Scouting: When greater than 6 beetles for every 100 plants is counted, treatment with an insecticide is often recommended.

Billbug

• Order: Coleoptera (Family Curculionidae)

• Southern corn billbug: Sphenophorus callosus

• Maize billbug: Sphenophorus maidis

• Origin: Native to North America

• Distribution: Mid to lower Atlantic Coastal Plain as well as in the corn belt and Texas

Billbug Physical Description

• Adults 7-13mm long (1/4-1/2 inch)

• color: grey, brown, black

• Elongated rostrum

Billbug Life History

• One generation per year

• Adults overwinter, often along field edges

• Spring emergence coincides with corn planting

• Eggs laid in soil or plant stem cavities

• Larvae tunnel into soil or root crown and feed on root mass

• Adults emerge midsummer to early fall

Billbug Damage

• Corn seedlings up to 6-leaf stage are at greatest risk

• Feeding slits in lower stem

• Death of small corn plants

• Rows of oblong holes in expanded leaves

Billbug Damage

Billbug Management

• Parasitic wasp, Patasson calendrae, parasitizes the eggs of multiple Billbug spp.

• Crop rotation helps because Billbugs do not travel long distances and have narrow host range

• Early planting, if possible

• Postemergence insecticides are often used if 5% of seedlings show excessive damage/loss. Often this is in the form of field-edge spot treatment

European Corn Borer

• Order: Lepidoptera (Family Crambidae)

• Ostrinia nubilalis

• Origin: Europe. Introduced in early 1900’s

• Distribution: Eastern U.S.: West to Rocky Mountains, South to Gulf of Mexico, and North into southern Canada

European Corn Borer Description

• Mature larvae 19-25mm (3/4 - 1 inch)

• Dark brown head capsule

• Lighter colored body

• Two dark spots on dorsal side of each body segment

• Adult females light in color and larger than males

• Adult males darker in color and smaller than females

European Corn Borer Life History

• Voltinism: univoltine and multivoltine populations exist (presence is temperature dependent)

• Overwinter as mature larvae in corn stubble or ears

• 7-10 days in pupal stage

• First flight of adult ranges between April and June (depending on voltinism)

• Eggs deposited primarily on undersides of leaves

• Hatched larvae move immediately to the whorl, ear, or leaf collar

• Older larvae may tunnel into stem or remain where they are and pupate

Geography of European Corn Borer Voltinism

European Corn Borer Damage

• Larvae can bore into any area on the corn plant

• Frass is often found around outside of entrance holes

• Damage to the whorl or stalk is often a sign of European Corn Borer activity

• In the stalk, Corn Borer feeding interrupts nutrient flow and can cause stalk to break

European Corn Borer Damage

European Corn Borer Control

• Monitor populations with pheromone traps and blacklighting techniques

• Minimize number of overwintering sites by destroying plant material remaining from last planting

• Spraying is often done at times that coincide with adult flight

Corn Rootworm Adults

Corn Rootworm

• Order: Coleoptera (Family Chrysomelidae)

• Northern CRW: Diabrotica barberi

• Southern CRW: Diabrotica undecimpunctata howardi

• Western CRW: Diabrotica virgifera virgifera

• Distribution: All found in Pennsylvania

Corn Rootworm Adult Description

• Northern Corn Rootworm Adult: Long and oval ins shape. Pale to dark green in color. The body lacks markings

• Western Corn Rootworm Adult: Light yellow or green in color with three black stripes on the elytra (sometimes these stripes are hard to see)

Corn Rootworm Adult Damage

• Newly emerged adults feed on corn leaves

• Adults primarily feed on the pollen and silk, possibly leading to incomplete pollination

Adult Corn Rootworm Damage

Adult Corn Rootworm Management

• Crop Rotation

• Often in sweet corn, insecticides are used to prevent clipping of silks by adult CRW

• Economic Threshold: 0.5 adults per plant

• Changes in harvesting and planting dates

Armyworm

• Order: Lepidoptera (Family Noctuidae)

• Pseudaletia unipuncta

• Origin: Native to North America

• Distribution: U.S. East of Rocky Mountains and north into Canada

Armyworm Description

• Adult pale grey to light brown with a white dot on each wing

• Larvae are 3.7-4.1cm long (1 1/2-1 /3/5 inches)

• Larvae greenish brown in color with some white specks

• Head capsule yellowish brown

• Two orange stripes on each side and two dark stripes

Armyworm Life History

• 2-3 generations per year

• 1st generation: in May and June, 2nd & 3rd in July and August

• Overwinter as pupae in soil

• Adults fly north in April and deposit eggs at night in rows/clusters on lower leaves or in grass

• Larvae are evening feeders. In day are found in ground litter or soil

Armyworm Damage

• Often invade corn close to cereal grain fields

• Can either feed exclusively on leaf margins or strip the plant entirely

Armyworm Damage

Management of Armyworm

• Eliminate any grassy weeds in or adjacent to corn fields

• Outbreaks generally do not occur in warm dry weather because of the presence of predators and parasitoids

• Application of insecticide is often done when stand loss exceeds 10%

Common Stalk Borer

• Order: Lepidoptera (Family Noctuidae)

• Papaipema nebris

• Origin: Native to North America

• Distribution: East of the Rocky Mountains and north to southern Canada

Common Stalk Borer Life History

• Univoltine (1 generation per year)

• Overwinters as eggs

• Larvae hatch late April/ early May

• Tunnel into the stems of grasses

• Older larvae tunnel into stems of corn plants

• Older larvae tend to disperse to broad leaved weeds (e.g. Ragweed)

• Adults emerge in late August

Common Stalk Borer Damage

• Tunnel into corn stem above ground and climb to the whorl

• Tunneling causes wilt of younger corn plants

• Older plants often have discolored, wilted, or dead central leaves

• Whorl feeding leads to damaged leaves

Common Stalk Borer Damage

Management of Common Stalk Borer

• Rotate corn with nonhosts, such as soybeans and alfalfa

• In some areas, natural enemies are effective in controlling populations

• Edge infestations are often controlled by removing any edge hosts where eggs may be laid (often burning or mowing tactics)

Slugs

• Phylum: Mollusca  Class: Gastropoda

• Gray Garden Slug: Deroceras reticulatum

• Origin: Introduced from Europe

Physical Description of Slugs

• 25-50mm long (1-2 inches)

• gray to pale brown in color

• Often has dotted / streaked pattern on dorsal surface

• Eyes on Stalks

Slug Life History

• Eggs deposited on soil in masses, surrounded by a yellow substance

• Eggs hatch in a month (small slugs)

• Overwinter as eggs and adults

• Number of survivors is dependant on harshness of winter

Slug Damage

• Feeding can be on germinating seeds, seedlings, or foliage

• Damage to whorls by slugs may retard plant growth

Slug Management

• Tillage to prevent residues (which attract slugs)

• Use of row-cleaners to remove residues if filed is a no-tillage field

• Application of molluscicide bait if damage is severe enough