Famer's Guide: Introduction To Corn Rootworm Larvae

Corn plants dwarfed and dying, underdeveloped kernels or malformed ears, could be signs of diabrotica species of the corn rootworm.

What is it?

Corn rootworms are the of the adult beetles of the diabrotica species. Corn rootworms as both young worms and adult beetles can be extremely damaging to corn plants in the garden causing dwarfed or dying plants.

What does it look like?

Corn rootworm larvae are either soft white to pale yellow in color. Corn rootworm larvae always have a dark to light brown head which extends from the front of thewir small 1/2 to 1/4 inch grublike bodies. Damage from corn rootworms in the larval form can result in chewed corn roots and leaves. Other damage may appear in the form of partially developed kernels or malformed ears of corn. Additionally, corn rootworm larvae damage may be the catalyst for corn plants which are dwarfed or appear to be yellowing in the normally green areas of the corn plant. Corn rootworm larvae may also cause general weakness in the plant fibers which can result in the corn plants falling over easily in times of wind or rain.

How does it manifest?

Adult female beetles of corn rootworms lay eggs that are yellow or orangish in the soil which surrounds the corn plants. These eggs at the soil hatch into young corn rootworms which survive by feeding on the roots of the corn for several weeks. They tunnel into the corn plant roots and devour small root regions completely. Often corn rootworm larvae can also devour larger root systems over time as they continue to tunnel from small to large roots. After several weeks of feeding, the corn rootworms pupate in the soil and emerge as mature adult beetles. Usually the adult corn rootworm beetles emerge in late July or early August and they proliferate in areas where corn has grown for two or more years consecutively. Corn plants which are at most risk to be damaged from these insect pests are those which have been planted late or are surviving in drought conditions.



What can you do about it?

To control corn rootworm larvae before they infest your plants, treat the soil with a diazinon containing insecticide prior to planting. You can also treat affected plants which show signs of corn rootworm larvae damage by applying a methoxychlor containing insecticide to the soil. You will need to repeat applications of the insecticide two or three times at one week intervals as plants become reinfested. You should be able to stop treatments when damage no longer appears, however if reinfestation occurs you will need to treat the corn plants again. It is extremely important to discard severely damaged plants and to clean up any plant debris or weedy areas in the general vacinity of your corn plants. These areas promote insect egg laying, and the eggs can also over winter there to reinfest new plants in the spring.

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