How Do I Deal With Rootworm in My Corn?

Corn rootworm is one of the most economically significant corn pests in the world, and it is a real problem in the home garden too — particularly when corn is grown in the same ground year after year. The larvae feed directly on corn roots, pruning them back and disrupting water and nutrient uptake. Severely affected plants lean and topple in wind (a condition known as root lodging) and may produce undersized, poorly filled cobs even when standing.

How to identify rootworm damage

Rootworm larvae are small, cream-coloured grubs about 1–2 cm long, found in the soil among the corn roots from early June onward. The visible symptom above ground is plants that lean noticeably — typically in a "goose-necking" pattern where the stem bends at the base as the plant tries to right itself. Digging up a suspect plant reveals roots that are pruned short, often to the crown, sometimes with a brown slimy appearance where the larvae have been feeding. Healthy corn roots should be white and extend well into the surrounding soil.

Crop rotation is the primary control

The corn rootworm lifecycle is intimately tied to corn: adults lay eggs in corn ground in late summer, and the eggs overwinter in that soil, hatching the following spring just as young corn roots become available. A single year of not growing corn in a given bed breaks this cycle completely, because the larvae that hatch find no corn roots and die. Rotate corn out of any bed for at least one season. This is the most effective, chemical-free control available.

What if rotation is not possible

In small gardens where rotation space is very limited, beneficial nematodes (Steinernema feltiae or Heterorhabditis bacteriophora) applied to moist soil in spring before corn roots develop provide biological control of soil-dwelling larvae. They are sold as a powder or in sponge form and are mixed with water for soil drench application. Results are variable but they can reduce larval populations without chemicals.

Adult beetle feeding on silks

The adult corn rootworm beetles emerge in mid-summer and feed on corn pollen and silks in large numbers. Heavily infested silks that are eaten back before pollination is complete can reduce cob fill. Row cover during the silking period excludes adults, but must be removed during active pollination or you will exclude wind-borne pollen too. In most home gardens the adult feeding is tolerable, with the root damage being the more serious problem.