Scouting for seedling insects

John Van Duyn, North Carolina State Yniversity, Entomology Extension Specialist

Scouting seedling corn on a weekly basis from emergence until plants are about 12 inches tall provides information on insect abundance, stand loss, and plant population. Equipment used for sampling includes a measuring device (e.g. a yard stick) , record form or booklet, pencil, and a digging device (e.g. a hand trowel). Target pests include armyworm, billbug, cutworm, stalk borers and soil insects (wireworm, seed corn maggot, rootworm, etc.).

Sampling Pattern and Procedure. Walk a zigzag pattern over the field looking for insect damaged plants. Damaged plants may be wilted (especially the whorl leaf), discolored, cut-off, or show foliage feeding; a poor stand may also indicate insect damage. When insect damage or poor stands are observed, the insect (or other cause) is identified by digging-up the plant or seed and examining for insect feeding signs. If the problem involves insects, 99 more plants (33 per row for 3 adjacent rows) are examined in the same area of the field (total of 100 plants); record the number of damaged plants (don't count plants with only minor feeding as damaged). After taking the first sample, nine additional randomly selected places in the field are sampled by examining 100 plants on three or more rows. After the first sample, digging plants should not be necessary. Take 10 samples per field unless after four (4) samples it is obvious that pests are well above threshold, then sampling can be discontinued. Note that if no insect damage is observed while walking through the field to initiate the first sample, then samples will not be taken.

In fields where billbug are a threat, special attention should be given non-rotated corn fields and to field edges bordering last year's corn fields. In the case of field edges, it may be necessary to scout an area approximately 150 - 200 feet wide on the edge side of the field as a separate field. In no-tillage situations, be more aware of foliage and stalk damage from armyworm, cutworm and stalk borer.

In the case of wireworm and other soil insects, there are no remedial treatments but scouting information can be important for future reference, determining the performance of the soil insecticide applied (if one was used), and evaluating plant stand information.

Plant stand estimation is done by counting plants on 10 row feet; 2, 5 foot sections of adjacent row at a minimum of 4 sites and 10 sites maximum. Calculate the average plants per row foot (total plants divided by row feet) and multiple by 17424 (30 inch rows), 14520 (36 inch rows), 13754 (38 inch rows) or 13068 (40 inch rows) to obtain plants per acre. This information can be helpful in determining the importance of further plant loss to insects; for evaluating the performance of planters, seed or chemicals; and for considering replanting.

Feeding Signs and Symptoms of Seedling Insects. Seedling insects can often be identified by the plant damage caused. The following list presents the most common damage symptoms:

Thresholds for Seedling Insect Pests. These thresholds assume a full stand; reduce the threshold by 1/3 if thin stands are encountered.

Corn Page

Other Resources

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This page (http://www.ces.ncsu.edu/plymouth/pubs/ent/crscouta.html) was created by John W. Van Duyn Ph D. Extension Entomologist, Wayne Modlin, Res. Tech. III.

Date Created 1/30/01.
Last revised on 1/31/04.

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

CAUTION: The information and recommendations in these Notes were developed for North Carolina conditions and may not apply elsewhere.