What is it?
Corn rootworms are the larvae and 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.
What does it look like?
The adult beetles are often brownish-red although some are yellow or a pale green shade. Some beetles, though not all, may have black stripes or spots on their bodies as well. They are distinctive because of their extremely long antennae that extend from the front of their bodies.
The larvae are either soft white to pale yellow in color. Damage from corn rootworms in either their larval or adult forms can result in chewed roots and leaves. Other damage may appear in the form of partially developed kernels or malformed ears of corn because the adult beetles feed on the silk and tassels of the corn which interrupts the pollination process.
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 worms which survive by feeding on the roots of the corn for several weeks. After several weeks of feeding, the corn rootworms pupate in the soil and emerge as mature adult beetles.
Usually, the 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 that 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 rootworm larvae before they infest your plants, treat the soil with a diazinon-containing insecticide prior to planting. However, if you find adult beetles present on your ears of corn and plants, you can treat them with an insecticide containing carbaryl.
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.