Create Your Garden

Corn Rootworms

Family Diabrotica spp.

Corn Rootworm

Host Plants

Corn rootworms are the scourge of corn, particularly in the Midwest of the United States.

Regions impacted

Found throughout North America, especially in the midwestern corn-growing areas such as Iowa. Also present in other temperate climates, including in northern Europe.

Description

Corn rootworms are a devastating pest of cultivated corn in North America. While adults can feed on a variety of plants, their larvae survive exclusively on the roots of corn. There are three primary corn rootworm species in North America:

  • Northern rootworm – most prevalent throughout the corn belt. The adult of the northern corn rootworm is tan to pale green and about 1/4 inch (6 mm) long. Newly emerged beetles are usually cream or light brown but gradually turn green with age. Male and female beetles have similar coloration, however, female beetles are typically larger than their male counterparts.
  • Western rootworm – also impacts the corn belt. Western corn rootworm adults are yellow to green in color with a black stripe along the sides of their wing covers and are about 5/16 inch (7.5 mm) long. Male wing covers are usually entirely black and darker than those of females, which can appear with striped patterns.
  • Southern corn rootworm – found throughout the U.S. but rarely causes serious damage. The southern corn rootworm adult is about 3/8 inch (9 mm) long, yellow to green, with 12 conspicuous black spots on its back. This species is also known as the twelve-spotted cucumber beetle.

It is difficult to distinguish between larvae of the western and northern species. Rootworm larvae are white and slender, about 1/2 inch (13 mm) long when fully grown, and sporting brown heads.

Life Cycle

Western and northern corn rootworms have only one generation per year. Eggs of both species are deposited in the soil by female beetles from mid-summer until fall. The eggs overwinter and begin hatching from late May to early June in most areas of the Midwest. The newly hatched larvae seek out and feed on corn roots. The rootworms pass through three larval instars, then in late June/early July pupate in soil near the corn roots. After 5 – 10 days, adults emerge, with males appearing a week or so before the females. Mating takes place a short time later. Within two weeks of emergence, females begin laying eggs, usually toward the end of July, with peak egg laying occurring in early to mid-August.

Damage and Detection

  • Both corn rootworm larvae and adults can damage corn plants.
  • The beetles feed on the foliage, pollen, silks, and developing kernels of corn. The latter attacks can interfere with pollination and germination, negatively impacting kernel production.
  • Larvae are very disruptive to the root system, feeding primarily on root hairs and outer root tissue. As larvae mature, they burrow more deeply into the roots to feed. Damage can include extensive root injury and the development of secondary infections.
  • Roots damaged and weakened by rootworms may topple or grow in a hunched “gooseneck” shape. These plants can pollinate poorly and are more difficult to harvest.
  • Western corn rootworm beetles can also wreak damage by feeding on the green tissue of the leaves. Unless feeding in abundance, these beetles are not usually dangerous to the crop but can indicate a large adult population which may impact the next season’s roots.

Prevention and Control

To mitigate the impact that larvae can have on the roots of corn, the following are recommended:

  • Space permitting, rotate the field annually. Rotating a distance of a few feet will be sufficient as the newly hatched larvae cannot move very far. Rotating to legumes can starve the bulk of the larvae within the year. Rotation to grasses such as wheat or rye is also effective. Even a 2-year rotation can be effective as rootworm populations take time to move and establish.
  • Encourage natural predators such as birds and competing ground beetles by creating some permanent beds or mulched pathways where the soil will remain undisturbed;
  • Maintain a tidy garden to give corn rootworm beetles fewer places to hide during the winter;
  • If applying a soil insecticide, follow the directions closely. Insecticides do protect the roots but are not as effective as rotation – you can get rootworm population growth in unprotected areas even when soil insecticides are applied.
While every effort has been made to describe these plants accurately, please keep in mind that height, bloom time, and color may differ in various climates. The description of these plants has been written based on numerous outside resources.

Related Items

Please Login to Proceed

You Have Reached The Free Limit, Please Subscribe to Proceed

Subscribe to Gardenia

To create additional collections, you must be a paid member of Gardenia
  • Add as many plants as you wish
  • Create and save up to 25 garden collections
Become a Member

Plant Added Successfully

You have Reached Your Limit

To add more plants, you must be a paid member of our site Become a Member

Update Your Credit
Card Information

Cancel

Create a New Collection

Sign Up to Our Newsletter

    You have been subscribed successfully

    Join Gardenia.net

    Create a membership account to save your garden designs and to view them on any device.

    Becoming a contributing member of Gardenia is easy and can be done in just a few minutes. If you provide us with your name, email address and the payment of a modest $25 annual membership fee, you will become a full member, enabling you to design and save up to 25 of your garden design ideas.

    Join now and start creating your dream garden!

    Join Gardenia.net

    Create a membership account to save your garden designs and to view them on any device.

    Becoming a contributing member of Gardenia is easy and can be done in just a few minutes. If you provide us with your name, email address and the payment of a modest $25 annual membership fee, you will become a full member, enabling you to design and save up to 25 of your garden design ideas.

    Join now and start creating your dream garden!

    Find your Hardiness Zone

    Find your Heat Zone

    Find your Climate Zone