Corn Rootworm
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Written by Mark Jeschke, Ph.D., Agronomy Manager
Key Points:
- Corn rootworm is the most damaging insect pest of corn in North America.
- Both larvae and adults can cause damage to corn – larvae feed on roots, which can lead to lodging, and adults feed on silks, which can interfere with pollination.
- Corn rootworm populations have proven adaptable in overcoming control methods, making it important to employ best management practices and use multiple control tactics.
Corn Rootworm Species
- There are four corn rootworm species in North America:
- Western corn rootworm – Diabrotica virgifera virgifera
- Northern corn rootworm – D. barberi
- Southern corn rootworm – D. undecimpunctata howardi
- Mexican corn rootworm – D. virgifera zeae
- Western and northern corn rootworm are the most economically important and found throughout the Corn Belt.
- Southern corn rootworm can be found throughout the U.S. but rarely causes economic damage.
- Mexican corn rootworm is locally important in in Oklahoma and Texas.
Corn Rootworm Lifecycle
- Western and northern corn rootworm go through one generation per year.
- Larvae begin hatching from late May to early June in most areas of the Corn Belt. Newly hatched larvae seek out and feed on corn roots.
- The larvae pass through three stages, or instars, before pupating in the soil. Most larval damage to corn roots is caused by the later instars.
Corn rootworm larvae feeding on a corn root. (Image courtesy of Jim Kalisch, University of Nebraska.)
Western Corn Rootworm
Has three stripes, or one broad stripe, on the wing covers. The legs are partially black but not banded.
Northern Corn Rootworm
Solid green color. Newly emerged adults may be tan or light yellow in coloration. No stripes or spots on the wing covers.
Southern Corn Rootworm
Also known as the spotted cucumber beetle. Has a black head, green pronotum, and 12 black spots on the yellowish-green wing covers.
Mexican Corn Rootworm
Legs are dark colored. Wing covers are often a mixture of yellow, green, and light blue and lack distinctive stripes.
- Adult rootworms begin to emerge from corn fields in late-June and early-July.
- Rootworm beetles disperse and mate, and can feed on pollen, green silks, or leaves in corn fields.
- Rootworm beetles can move between fields and may feed on corn in fields other than where they emerged.
- Female beetles deposit eggs in the soil from mid-summer until autumn where the eggs overwinter.
Corn rootworm larvae on a heavily damaged corn root.
Larval Injury to Corn
- Corn rootworm feeding on the roots reduces the plant’s capacity to take up water and nutrients.
- A damaged root system can also predispose the corn plant to fall over in wet or windy conditions.
- Often this lodging occurs prior to tasseling, and the plant attempts to grow upright, causing a tangled condition known as “goose-necking”
- Injured roots are also easy entry points for fungi and bacteria that may increase severity of root and stalk rots and premature death.
Northern corn rootworm beetles feeding on silks and kernels.
Untreated conventional corn hybrid is root lodged as a result of corn rootworm larval feeding followed by a thunderstorm.
Adult Injury to Corn
- Adult corn rootworms feed on green silks and can prevent silks from capturing pollen.
- In commercial corn fields, large beetle populations are necessary to cause economic damage and to justify an insecticide application.
- Western corn rootworm beetles can also cause damage by feeding on the green tissue of the leaves.
Corn Rootworm Management
- Corn rootworm populations have proven adaptable in overcoming control methods, making it important to employ best management practices and use multiple control tactics.
- Historically, rotation with a non-host crop such as soybean was a very effective management strategy; however, some rootworm populations have adapted to overcome this tactic.
- A variant of western corn rootworm has evolved to lay eggs in fields other than corn, so larvae are present even when a field was not in corn the preceding year.
- The extended diapause variant of northern corn rootworm deposits eggs in the soil that do not hatch the following spring, but instead survive in the soil until the following year when the field is rotated back to corn.
- Pioneer and university research suggests that continuous, uninterrupted use of the same corn rootworm Bt technology can lead to reduced product efficacy against these insects.
- Management selections may be aided by a careful scouting program that monitors adult presence and potential egg laying, allowing rough prediction of a future problem and the need for applying specific control measures.
- Please contact your Pioneer Sales Professional for more information.
What Leads to High CRW Populations Surviving Overwintering?
We may complain about 🥶, but winter plays a key role in killing off unwanted pests. So, how do factors like snow, freeze and moisture levels affect corn rootworm populations? Tune into Crop Doctorate to find out.
The foregoing is provided for informational use only. Please contact your Pioneer sales professional for information and suggestions specific to your operation. Product performance is variable and depends on many factors such as moisture and heat stress, soil type, management practices and environmental stress as well as disease and pest pressures. Individual results may vary. Pioneer® brand products are provided subject to the terms and conditions of purchase which are part of the labeling and purchase documents.