Agronomic Crops

Pests Belowground
Southern Corn Rootworms, Seedcorn Maggots, Sugarcane Beetles, Lesser Corn Stalk Borers,
Corn Billbugs, White Grubs, Wireworms, Cutworms
Most insects that attack plants at or beneath the soil surface are most damaging to corn in the seedling stage. Although many of
these insects may damage older plants, seedling corn is the most likely to be injured. Many late-season pests can usually be avoided
by early planting. Early planting reduces the chances of insect infestations and increases yield potential. A major factor in corn insect
pest management is controlling soil insects that threaten corn stands and overall plant health. e occurrence of soil insects is
often spotty. But certain factors, such as reduced tillage, no-till corn, and fields with a history of soil insects warrant the use of insecticides
or seed treatments at planting. e use of these products is justified when the potential for infestation is high and when
rescue treatments offer less control. ese products are used for prevention.
southern Corn Rootworms
e adult southern corn rootworm is also known as the twelve-spotted cucumber beetle. Adults are found on many plants
throughout the growing season. Females deposit their eggs at the base of the plants. Upon hatching, the larvae move into the root
zone and begin feeding. e larva is about one-half inch long when full sized. It has three pairs of small legs just behind the head
and brownish patches on the head and tail end.
DAMAGe: Larvae damage corn seedlings by feeding on and tunneling inside the roots. Larvae may also bore inside the stem just
above the roots to feed on the crown of the plants, eventually killing the bud. Damaged plants often wilt, and you can find evidence
of rootworm feeding if you dig up the plant and examine the root system. Severe feeding and root pruning may cause plants
to lodge. is is often called “goose necking.”
ContRoL: Pre-emergence insecticides are recommended when planting after a legume crop. Treated seed will also offer control
of southern corn rootworms.
tHResHoLD: Treatment is preventive. See the table on page 50 for products used to control/suppress belowground pests.
seedcorn Maggots
e seedcorn maggot is the larval stage of a fly. It feeds on decaying organic matter in the soil. Larvae are less than one-fourth
inch long, pale white, and they lack legs or an obvious head.
DAMAGe: is pest attacks the germinating seed planted in cool, wet weather or corn planted to fields with freshly decaying
vegetation. Heavy infestations will reduce stands and cause stunting of the plants.
ContRoL: Damage can be prevented with the use of soil insecticides at planting or seed treatments.
tHResHoLD: Treatment is preventive. See the table on page 50 for products used to control/suppress belowground pests.
sugarcane Beetles
is insect occurs sporadically from year to year. is beetle is black and about one-half inch long. When this pest is abundant,
it can destroy stands in isolated fields. Control of this pest has been inconsistent with soil insecticides.
DAMAGe: e sugarcane beetle feeds on the stem at or slightly below the soil surface. Feeding damage appears as a ragged hole
in the base of the stem.
ContRoL: e use of soil insecticides at planting or seed treatments may suppress sugarcane beetle infestations.
tHResHoLD:: Treatment is preventive. See the table on page 50 for products used to control/suppress belowground pests.
Lesser Cornstalk Borers
Infestations of lesser corn stalk borers occur most often during dry weather conditions in sandy soils. Sometimes silken tubes
containing larvae can be found attached to plants when they are dug up for inspection. Larvae are slender and greenish, and usually
wiggle violently when disturbed.
DAMAGe: Larvae damage the corn plant by boring into the base of the stem. Damage can cause deadheart and may greatly reduce
stands. Plants that experience deadheart die or are severely stunted and never produce a harvestable ear.
ContRoL: e use of soil insecticides at planting or seed treatments offer control/suppression of infestations.
tHResHoLD: Treatment is preventive. See the table on page 50 for products used to control/suppress belowground pests.
Corn Billbugs
e larvae of billbugs (snout-beetles) feed on roots and bore into the stems of corn plants.
DAMAGe: Feeding by the adults will appear as a row of holes across the leaf when it unfurls.
ContRoL: Soil insecticides at planting or seed treatments offer some control/suppression of infestations.
tHResHoLD: Treatment is preventive. See the table on page 50 for products used to control/suppress belowground pests.
50 Crop Corn Name