Home

Diseases of  Alfalfa  Corn  Soybeans  Wheat

Insect Pests of  Alfalfa  Corn  Soybeans  Wheat

Weeds  Identify  Monocots  Dicots  Grasses  Sedges  Lilies  Broadleaf

Scout Info
Kentucky IPM Pest Information Pages

Corn Rootworm Beetles: Kentucky Corn IPM

Corn Rootworm Beetles


Description

Three species of corn rootworm beetles are found in Kentucky.

Larvae of all three species of corn rootworms have cylindrical white to cream bodies with a brown to black head and a pair of small legs on each of the first three segments behind the head. There is a small brown or black area on the top of the last segment. Full grown (last instar) larvae are about 1/2 inch long.

Northern Corn Rootworm

The northern corn rootworm adult is pale green to yellow and about 1/4 inch long.

Southern Corn Rootworm

The southern corn rootworm adult (also called the spotted cucumber beetle) is about 3/8 inch long. It is yellow-green with 11 conspicuous black spots on the wing covers.

Southern corn rootworm

Western Corn Rootworm

The western corn rootworm beetle is yellow with three black stripes on the wing covers. It is relatively new in Kentucky. If you suspect them in a field, collect some for identification.

Western corn rootworm feeding on silks

Damage

Larvae

Rootworm larvae feed on corn roots for about three weeks. As a result, corn leaves may develop a yellow cast and plants may show symptoms of nutrient deficiency or drought stress due to root damage by the time the corn height reaches knee-high. Infestations may be limited to rough circular areas within fields. Damage may occur in fields that were in corn the previous year. Corn plants may
lodge, or fall over, if enough root damage occurs.

Soil compaction, drought stress and other factors can produce symptoms similar to rootworm damage. The presence of rootworm larvae should be confirmed by examining root systems for larvae and chewing damage.

Adults

Adult rootworm beetles feed on the developing corn silks. This is of concern only if adults are present in the field before and during the maximum period of pollen shed. If the field will be planted in corn again the following year, northern and western corn rootworm beetles pose a threat in that larvae will be present in the soil, ready to attack the next year's crop. Southern corn rootworms are important only as silk feeders.

Pest Activity

Larvae
Rootworm Larval Activity>
<P><B>Adults</B><br>
<IMG SRC=

Please note: These dates are approximations only. This calendar was constructed using data from Kentucky, USA. These dates may not apply in your area. You may wish to contact your county extension agent or agricultural consultant for information tailored to your locality.

IPM Techniques and Scouting Procedures

Larvae

Rootworm larvae may be found from mid- through late June. Watch for irregular growth patterns and stress symptoms.

To scout for rootworm larvae:

  • Dig up a 6" cube of soil containing the root zone of stressed plants. Carefully break away the soil from around the root zone and look for rootworm larvae and evidence of chewing on the plant roots.

  • Indicate infested areas of the field on a field map. If you encounter lodging, record the percentage of lodged plants in random areas of the field. This is done by examining groups of 20 consecutive plants and recording the number bent or lodged. Compute the percentage as explained in the cutworm section.

  • Immediately inform your supervisor if you find rootworm damage in a field. Soil compaction, drought stress and other factors can produce symptoms similar to rootworm damage. Confirm your diagnosis by examining root systems for larvae and chewing damage.

Adults

Look for adult rootworm beetles from mid-July through silking. Silk feeding is a problem only if it occurs before and during the maximum period of pollen shed.

If you do not see any beetles as you walk through the field, do not spend your time surveying. However, if beetles are active, follow these guidelines.


This site was created and is maintained by Pat Dillon, Department of Entomology, University of Kentucky, S-225 Agricultural Science Ctr North, Lexington, KY USA  40546-0091 (phone: 859/257-3571). Please send questions or suggestions to: pdillon@uky.edu