Description of the Pest
Eggs of the beet armyworm are deposited in masses that are covered with a white cottony material. The larvae are about 1.25 inches long when full grown. They are mottled olive green to almost black. Eggs of the western yellowstriped armyworm are similar to those of the beet armyworm. The egg masses are larger and covered by a gray cottony material. The larvae attain a length of 1.5 to 2.0 inches, are black with a prominent yellowish stripe and several narrow bright stripes on each side of the body. An intense black spot is usually visible on each side of the first legless segment behind the head.
Damage
Armyworms skeletonize leaves when feeding in colonies shortly after hatching. Larvae that are half grown or more will feed singly on leaves and bean pods. Damaged pods will have holes in the pods and beans.
Management
While armyworms may be present anytime from June through September, numbers are usually most damaging in late summer. Insecticide applications will be most effective if applied when larvae are young.
Biological Control
Common natural enemies of armyworms include the parasitoid, Hyposoter exiguae, which lays an egg that hatches into a green larva inside the parasitized armyworm. To determine if caterpillars are parasitized, pull worms (at least 0.5 inch long) apart to see if light green parasitic wasp larvae are inside. Additionally, there are numerous general predators that attack armyworms, including assassin bugs, damsel bugs, and spiders. Plant habitat that attracts natural enemies and avoid use of broad-spectrum pesticides known to harm natural enemies.
Organically Acceptable Methods
Use biological control, Bacillus thuringiensis, and the Entrust formulation of spinosad for an organically certified crop.
Monitoring and Treatment Decisions
Start inspecting for armyworm damage during the vegetative growth stage. Continue looking during the flower bud to bloom and pod fill stages. Specific treatment thresholds have not been established for armyworms on beans. Insecticide applications are seldom necessary.
Pesticides and Natural Enemy Releases
Not all registered pesticides are listed. The following are ranked by their IPM value, with the most effective and least harmful to natural enemies, honey bees, and the environment listed at the top of the table. When choosing a pesticide, consider information related to water and air quality, resistance management, and the pesticide's properties and application timing. Use PestManage to compare summarized management options for different pests in the same crop. Always carefully read the label of the product being used and take all necessary precautions when handling pesticides.
| Rank | Active ingredient | Example trade name | Group | Group Order | MoA 1 | Amount per acre | REI (hours) ‡ | PHI (days) ‡ | Comments | Selectivity 2 | Bees 3 | Predatory mites 4 | Predators 5 | Parasitoids 5 | Residue duration 6 | Leaching(fish) 7 | Adsorbed runoff(fish) 8 | Solution runoff(human) 9 | Leaching(human) 10 | Solution runoff(human) 11 | Last updated 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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XenTari # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
11A |
0.5–2.0 lbs | 4 | 0 | Control is maximized by thorough good co... | narrow | low | low | low | short | — | — | — | — | — | 06/2018 | ||
|
|
Coragen | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
28 |
3.5–5.0 fl oz | 4 | 1 | — | narrow | low | low | low/moderate | short | — | — | — | — | — | 06/2018 | ||
|
|
Steward EC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
22A |
6.7–11.3 fl oz | 12 | 7 | — | narrow | low | low | low | moderate | low | low | intermediate | very low | low | 06/2018 | ||
|
|
Intrepid 2F | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
18 |
4.0–16 fl oz | 4 | 7 | Early season applications: 4 to 8 fl oz;... | narrow | low | low | low | short | very low | low | low | very low | low | 06/2018 | ||
|
|
Entrust # | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
1.25–2 oz | 4 | 28 | Do not apply more than 3.75 oz per acre... | narrow | low | moderate 13 | low/moderate | short to moderate 13 | very low | low | low | very low | low | 06/2018 | ||
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|
Success | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
5 |
4.0–6 fl oz | 4 | 28 | Do not apply more than 12 oz per acre pe... | narrow | low | moderate 13 | low/moderate | short to moderate 13 | very low | low | low | very low | low | 06/2018 |
Legend
- ‡ a b Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
- # a b Acceptable for use on certified organic crops. Check with your certifier to confirm before application.
- 1 ↩ Group numbers for insecticides and miticides are assigned by the Insecticide Resistance Action Committee (IRAC). Insecticides with unknown modes of action are assigned mode-of-action group numbers (MoAs) that begin with UN. Rotate pesticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B.
- 2 ↩ Range of insect and mite groups affected by a pesticide. Broad means the pesticide affects most groups of insects and mites; narrow means the pesticide affects only a few specific groups.
- 3 ↩ Risk of harm to honey bees. For more information, see Bee Precaution Pesticide Ratings.
- 4 ↩ Risk of harm to predatory mites. Toxicities are generally to western predatory mite, Galendromus occidentalis. Where differences have been measured in toxicity of the pesticide-resistant strain versus the native strain, these are listed as pesticide-resistant strain or native strain.
- 5 a b Risk of harm to parasitoids and general predators. Toxicities are averages of reported effects and should be used only as a general guide. Actual toxicity of a specific insecticide depends on factors including the application rate, environmental conditions, and the life stage and species of a parasitoid or predator.
- 6 ↩ Length of time residue affects natural enemies. Short means hours to days; moderate means days to 2 weeks; and long means many weeks or months.
- 7 ↩ Risk of harm to fish from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 8 ↩ Risk of harm to fish from adsorbed runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 9 ↩ Risk of harm to fish from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 10 ↩ Risk of harm to humans from leaching, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 11 ↩ Risk of harm to humans from solution runoff, based on USDA Natural Resources Conservation Service Windows Pesticide Screening Tool (WIN-PST).
- 12 ↩ Date information was last updated in the UC IPM Pest Management Guidelines.
- 13 a b c d Toxic to some natural enemies (lacewing and syrphid fly larvae, predatory beetles, and thrips) when sprayed and up to 5 to 7 days after.
UC IPM Pest Management Guidelines: Dry Beans
UC ANR Publication 3446
R.F. Long (emeritus), UC Cooperative Extension Yolo County
P.B. Goodell (emeritus), UC IPM and Kearney Agricultural Research and Extension Center, Parlier
Acknowledgement for Contributions to Invertebrates
L.D. Godfrey, Entomology, UC Davis
