How to Manage Corn Rootworm
Corn rootworm, a persistent and damaging pest, can significantly reduce yields and compromise the overall health of corn plants. Proactive field scouting, pest identification and chemical management with products like GCS Bifenthrin 2EC** and Willowood Imidacloprid 4SC can help.
This comprehensive guide will review:
How corn rootworm affects crops
How to identify corn rootworm
Regions typically affected by corn rootworm
When corn rootworm usually affect crops
Chemical products to control corn rootworm
What Is Corn Rootworm?
There are three species of corn rootworm, which can only be identified during the adult beetle stage:
1. Western Corn Rootworm (WCR)
Western Corn Rootworm (WCR) is the most common rootworm beetle and most damaging species across the Corn Belt. The adult beetle is yellow or light green with three black stripes running the length of the wings. Stripes vary from three distinct dark to black lines on the males to one large strip covering most of the wings on the females. Females have slightly larger abdomens than do the males, but both are around 5/16-inch long.
2. Northern Corn Rootworm (NCR)
Northern Corn Rootworm (NCR) are usually found in smaller numbers than WCR in the northern portion of the Corn Belt. NCR have the unique ability to enter an extended diapause stage, meaning they can remain in the egg stage of its life cycle for an extra year. This allows NCR to survive in a one-year crop rotation system. NCR range from tan to lime green in color and reach about ¼ inch long. Unlike the WCR and SCR beetles, there is no color difference between males and females; however, females typically have longer, larger abdomens.
3. Southern Corn Rootworm (SCR)
Also known as the Spotted Cucumber Beetle, the Southern Corn Rootworm (SCR) generally causes the least damage of the three pest types, but there can be situations where adult SCR beetles must be controlled to protect against silk clipping during corn pollination. SCR eggs do not survive the winter in most of the Corn Belt, but they are still of some concern in the southern Corn Belt. The adult beetles are yellow to light-green with 12 black dots on the back and are generally around ⅜-inch long.
These three pest species, when combined, cost U.S. farmers around $1 billion every year when factoring in yield losses and input expenses. (1)
The corn rootworm life cycle follows the stages below:
There is only one generation of corn rootworm per year. Here is a more detailed look at their life cycle:
Rootworm eggs hatch. The rootworm eggs hatch in the spring and the larva move to the roots of seedling corn plants from mid-May to mid-June.
The larva feed and enter the roots. Larvae hollow out the roots and end up pruning the roots limiting the roots ability to absorb nutrients and water. Severely pruned roots also reduce the standability of the corn plant, and can cause corn plants to lodge, making harvest difficult resulting in possible corn ear loss.
Larvae exit roots and pupate in the soil. When corn rootworm larvae reach full size (sixth instar stage), they exit the roots and pupate in the soil near the roots. Both larvae and adult beetle feeding can provide entry points for secondary pests and disease.
Adults leave the soil and mate. Adult rootworm beetles emerge from the soil in late June to mid-August and then mate. Adult rootworm beetles also feed on corn silks during the pollination period causing poor pollination of the ear and limiting the number of kernels to be produced.
Females deposit eggs. Approximately 14 days after emergence, the female rootworm beetles deposit their eggs into the soil near the corn plant’s root zone. High populations of rootworm beetles can scrape the chlorophyll from corn leaf surfaces. This results in less leaf area to manufacture sugars to be translocated to the corn kernels, limiting kernel fill.
How Do Corn Rootworms Affect Corn?
An individual corn rootworm can lay anywhere from 500-1,800 eggs, depending on the species.
Corn rootworm larvae feed on corn plant roots, impairing their ability to absorb water and nutrients from the soil, stunting their growth and making them more vulnerable to drought stress and diseases.
Adult corn rootworm beetles also scrape the chlorophyll from corn leaf surfaces, resulting in a reduction in leaf area to manufacture sugars to be translocated to the corn kernels, limiting kernel fill and translating to significant economic damage. They also feed on corn silks during pollination, leading to poor pollination and limiting the number of kernels produced.
Rootworm beetles will also migrate to soybean, alfalfa and other crops where they feed on pollen, flowers and foliage, but typically they are not more than a nuisance outside of corn.
How to Identify Corn Rootworm
Corn rootworm larvae are small, white and worm-like with distinct brown heads. They can usually be found feeding on the roots of corn plants.
Adult corn rootworm beetles are around 1/4 inch long with yellow-green bodies and noticeable black stripes on their wings. They are most active during the summer months.
Key signs of corn rootworm infestation include:
Observing adult beetles feeding on leaves
Observing larvae in the root zone
Regions Affected by Corn Rootworm
Corn rootworm is particularly rampant in the Corn Belt, encompassing states like Iowa, Illinois, Nebraska and Indiana.
Timing of Dingy Cutworm Infestations
Corn rootworm infestation can occur at various stages of the corn growing season. Early-season infestations involve larvae feeding on the roots during the initial phases of plant growth, severely impacting crop establishment.
Late-season infestations occur when adult beetles emerge from the soil between late June and the middle of August, mate and, approximately 14 days after emergence, the female rootworm beetles deposit their eggs into the soil near the corn plant’s root zone. Adult beetles also feed on the leaves of mature corn plants, causing significant damage to foliage and energy production.
How to Chemically Manage Corn Rootworm
Insecticidal seed treatments provide systemic protection against early-season corn rootworm larvae. These treatments are applied directly to corn seeds before planting, interfering with larvae feeding and growth. However, they may not be sufficient for heavy infestations or long-term control.
Combining seed treatments with other integrated pest management strategies, such as crop rotation and targeted insecticide applications, is recommended for comprehensive control.
Once fields have reached a level of infestation at which chemical products are needed, several insecticides are labeled to control the adult beetles, and can be applied by air, ground or through a sprinkler system.
One popular option is GCS Bifenthrin 2EC**, an insecticide containing bifenthrin that is labeled for use with corn rootworm. Alternatively, Willowood Imidacloprid 4SC is another insecticide containing imidacloprid, which may also be labeled for use with corn to control rootworms. Another option is Willowood Lambda-Cy 1EC**.
Rotating between different modes of action helps prevent the development of resistance in corn rootworm populations, ensuring long-term sustainable pest management.
Protect Against Corn Rootworm with FBN Direct®
Proactively scouting for and responding to pest presence in your fields will help reduce potential crop damage and improve yield. FBN Direct has a wide variety of effective insecticides to help address pest pressures and keep your operation on track. With transparent pricing, straightforward online ordering, detailed product labels and fast direct-to-farm delivery, FBN Direct can help you get the products you need to protect your crops.
(1) Corn Rootworm Management Update, Iowa State University Extension and Outreach
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