The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.
The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.
From: Mark Abney, Extension Entomologist
North Carolina growers have observed armyworm (Fig. 1) and corn earworm caterpillars in sweetpotato fields across the eastern part of the state in the past couple weeks. While the feeding these insects do on the leaves rarely results in economic damage, they can be severe pests if they are allowed to get into bins of harvested potatoes. Caterpillars that are present on the foliage at harvest will begin to feed on exposed roots if the roots are not removed from the field soon after they are dug. The insects will feed on the surface of the roots, but are also capable of boring into the sweetpotatoes where they can easily be transferred to bins. Once in the bin, larvae will continue to feed and damage potatoes. Control options for caterpillars in storage bins are extremely limited.
Fortunately, caterpillars can be controlled effectively with insecticides in the field. It is important to note that infestations may not be uniform from field to field or even within a single field; fields should be scouted thoroughly before harvest to determine if caterpillars are present. Fall armyworm development may take from 14 to 30 days depending on temperature (development is more rapid at higher temperatures). The size and number of larvae present, and the time until harvest should be considered when making a control decision. Small larvae that are present now will likely still be in the field for another 10 to 20 days. If harvest is imminent, growers should select an insecticide with rapid knockdown and a short pre-harvest interval (Table 1). If you have any questions about controlling caterpillar pests in sweetpotatoes, contact your local county Extension agent or vegetable extension entomologist Mark Abney at 919-515-2745.
Table 1. Insecticides labeled for armyworm control in sweetpotatoes.
| Insecticide (trade name) | Rate | Pre-Harvest Interval |
| Zeta-cypermethrin (Mustang 1.5 EC) | 3.4 to 4.3 oz/acre | 1 |
| Deltamethrin (Decis 1.5 EC) | 1.5 to 2.4 oz/acre | 3 |
| Lambda cyhalothrin (Warrior II) | 1.28 to 1.92 oz/acre | 7 |
| Indoxacarb (Avaunt) | 3-6 oz/acre | 7 |
| Spinetoram (Radiant) | 6-8 oz/acre | 7 |
Fig. 1. Large armyworm larvae feeding on sweetpotato leaves.
Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
Last modified on September 24, 2009 by Stephen J. Toth, Jr.