Below-ground Pests of Corn

History of Corn as a Crop

•  Corn = Zea mays

• Originated in Central America

• Was domesticated more than 7000 years ago

• European Arrival to the New World: Corn was already grown as far north as New England

 Importance of Corn

• The most important “coarse grain” (feed for livestock) crop

• U.S. Produces approx 46% of world corn supply. China approx 10%

Corn Rootworm Larval Description

• Northern CRW: Diabrotica barberi

• Western CRW: Diabrotica virgifera virgifera

• Larvae are small. Grow to approx 16mm (5/8 inch)

• White body with brown head capsule and brown plate on last abdominal segment

Corn Rootworm Larva

Corn Rootworm Larval Damage

• Occur primarily in fields with multiple seasons of corn plantings

• Larvae feed on and inside of roots

• Larvae feed on root hairs

• Interference with water and nutrient transport

• Reduction in plant stability

• Lodging:CRW causes plants to fall over. These plants are unable to be harvested mechanically.

Damage of Larval Corn Rootworm

Corn Rootworm Larval Management

• Crop rotation = most successful control method

Black Cutworm

• Order Lepidoptera (Family  Noctuidae)

• Agrotis ipsilon

• Distribution: throughout continental U.S.,  southern Canada, Central & South America

Black Cutworm Description

• Larvae are black to pale gray in color

• each abdominal segment has 4 tubercles and a rough texture

• can grow to approx 45mm (1 1/2 inch)

• sometimes mistaken for crane fly larvae or millipedes

Black Cutworm

Black Cutworm?

Black Cutworm Life History

• Adults migrate from Gulf region in Spring, utilizing low level jet winds

• Migration is primarily in April and May

• Eggs deposited in grasses, especially in damp, low lying fields

• Early generation adults may move further North

Black Cutworm Life History

• Larvae are found 2-10cm below soil

• Adults migrate south during early Autumn, utilizing surface winds

Black Cutworm Damage

• 1-3rd instar feed on leaves of seedlings, leaving small “shot-holes” on the leaves

• 4-7th instar feed at night, often below soil, cutting the seedling

• Seedlings cut below soil often do not survive

• Older instars may tunnel into stalk, interrupting water and nutrient transport

Black Cutworm Damage

Black Cutworm Management

• Elimination of winter and early spring vegetation before planting

• Promotion of rapid seedling growth

• Trapping of adults with pheromone traps helps determine pest numbers

• Potential for control with the nematode, Steinernema carpocapsae  

Seed Corn Maggot

• Order Diptera (Family Anthomyiidae)

• Delia platura

• Distribution: Worldwide

• Description: maggot is white/light beige in color. Tapered at the front end. Head and legs are not visible

• Adult: smaller and thinner than a house fly

Seed Corn Maggot and Adult

Seed Corn Maggot Life History

• 4-5 generations per year above 43deg N

• 2-3 generations per year below

• Overwinters in puparium under the soil

• Adults emerge in spring

• Females lay eggs in recently plowed fields

Seed Corn Maggot Damage

• Maggots are the injurious stage

• Damage is often during periods of slow germination

• Damage is often in fields with decaying matter

• Maggots tunnel through the corn seed coat, killing the seed or decreasing the vigor of the emerging seedling

Seed Corn Maggot Damage

Seed Corn Maggot Management

• Plant seeds in shallow, warm and well prepared soils

• Avoid planting in fields with cover crops unless decomposition of organic matter has occurred

• Delay planting until after tillage

Wireworm

• Order Coleoptera (Family Elateridae)

• species within many genera in the family Elateridae

• Distribution: Widespread

• Description: long, cylindrical larvae. Often highly sclerotized, and yellow-brown in color

Wireworm

Life History of Wireworms

• Eggs often deposited in soils of cultivated fields or grassy areas

• Larvae take 1 to 5 years to develop into adults (merovoltine)

Wireworm Damage

• Bore into seeds before germination (early season injury)

• Wireworms tunnel in soil, which can damage roots or bend the plant

• In summer they may bore into plant stalks

Wireworm Damage

Wireworm Management

• Should be implemented before planting

• Baiting strategies often used to determine level of infestation

• Average of one wireworm per bait cup (filled with untreated corn and wheat seeds) is considered an economic infestation.

• Pesticides often used above economic infestation

White Grubs

• Order Coleoptera (Family Scarabaeidae)

• Annual White Grub = Cyclocephala immaculata

• True White Grubs = Phyllophaga spp.

• Origin: Native to North America

• Distribution: Most of U.S., with the exception of the Pacific Northwest

Description of White Grubs

• White, C-Shaped larvae

• 25mm (1 inch) long

• Often have a brown-orange colored head capsule

White Grub

White Grub Life History

• Annual White Grubs have 1 generation per year

• Adults emerge from soil in early summer (at dusk)

• Eggs are deposited in the soil

• Larvae hatch 2-3 weeks after egg deposition

• Larvae move down into soil in early fall and overwinter

• Larvae move upwards and pupate in early spring

White Grub Damage

• Annual white grubs feed on the roots of seedlings

• True white grubs strip the root hairs from the roots

• Plants will turn yellow if severely injured, and often die

• Some plants turn purple, indicating and inability to take up phosphorous

White Grub Damage

White Grub Management

• Scouting and identification of grubs is important in order to determine if there are true white grubs in the field. This can be done by taking soil samples

• 1ft by 1ft by 6 inches deep. Twenty per 40 acres

• 1 larva per sq. ft can indicate significant loss

• Planting time insecticides are often used

Sod Webworm

• Order Lepidoptera (Family Crambidae)

• Crambus spp.

• Origin: Native to U.S.

• Distribution: throughout U.S. and Canada

• Description: Larvae gray with black spots and coarse hairs

• Grow up to 2.5cm in length. Very active larvae

Sod Webworm

Sod Webworm Life History

• Overwinter as larvae in cocoons in sod fields

• Larvae feed in spring until late June, when they are fully grown

• Pupation occurs underground, near the corn plants

• Adults emerge in late August/early September

Sod Webworm Damage

• Feed below soil surface or at ground level

• Larvae cut the and eat the leaves

• Larvae chew holes in stems underground, causing plants to wilt

Sod Webworm Damage

Sod Webworm Management

• Injury is generally just in first year corn planted after sod

• Avoid planting on sod areas

• Plow sod in late summer before oviposition

• No established economic threshold