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Corn Rootworm - Part 1: Description of Corn Rootworm and Other Early Season Corn Pests

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Damage Caused by CRW Feeding

Corn Root Injury

The most damage to a corn crop occurs when the CRW are in the larval stage of development. At this stage of the lifecycle, the larvae feed on the roots of the corn plant. They will eat the primary roots and root hairs as well as the brace roots (exposed support roots). (FIG. 11)


Fig. 11: Corn root damaged by CRW feeding (Marlin E. Rice, ISU)

The larvae will tunnel into the roots, creating an opening for pathogens to enter the plant. Root rot is the most prevalent disease that occurs resulting from CRW feeding.  Feeding also compromises the plant’s ability to take up nutrients and water through the root system. This reduction of nutrients and water can result in a decrease in yield.

Fig. 12: Lodged corn (goose-necked) (Marlin E. Rice, ISU)


Larval feeding causes root pruning, which can cause a corn plant to lodge. Feeding on the roots not only allows pathogens to enter the plant, it also reduces the stability of the plant. Thus, given the appropriate conditions of moist soil and strong winds, corn plants can fall over (lodge). Once the plants have lodged, instead of dying they will continue growing. The plants grow vertically, but because of lodging a curving of the stalk results. This curve in the stalk is referred to as goose necking. (FIG. 12)




Leaf, Silk, and Kernel Injury
 
Fig. 13: Window pane effect caused by adult CRW beetles (Marlin E. Rice, ISU)

As the CRW enter the adult phase, feeding on the above ground plant parts also occurs. The beetles will feed on silks, exposed kernels on the ear, and on leaf tissue.  Western corn rootworm adults most often cause the damage that occurs to corn leaves. The WCR beetles will feed on corn leaves in the absence of corn silks, pollen, and ear tips. This usually happens when the beetles emerge prior to tassel emergence and pollination. Beetle feeding on leaf tissue results in a “window pane” effect. (FIG. 13)

Corn rootworm silk feeding, also known as silk clipping, results in silks being cut near the tip of the ear. This damage to the silks can result in poor ear fill due to the lack of successful fertilization.  When CRW beetles feed on exposed ear tips, it causes damage to the ear and creates an opportunity for disease-causing pathogens to enter the plant. CRW beetles also feed on pollen in the tassel when pollen shed begins. Although the beetles consume pollen, pollen flow is not usually compromised due to the large amount of pollen released within the field.

 

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