Description of the Pest
Darkling beetle adults are from 0.13 to 0.25 inch (3.5 to 6 mm) long and vary from black or blue-black to rusty brown. They may be hidden by dust or a thin veneer of soil. Do not confuse darkling beetles (Tenebrionidae) with predaceous ground beetles (Carabidae), which prey on various soil dwelling pests. Darkling beetles generally have clubbed antennae whereas predatory ground beetles do not.
Larvae are cylindrical, soil-inhabiting, wormlike insects that resemble wireworms, the larvae of the click beetle. Darkling beetle larvae are light yellow to dark brown and range from 0.03 to 0.33 inch (0.8 to 8 mm) in length. They are often referred to as false wireworms.
Development from egg to adult can take up to 50 days during summer. Eggs hatch in 3 to 6 days, followed by about five larval instars. The pupal stage lasts 8 days or longer. Beetles are most numerous in spring and early summer, often found under clods or organic debris during daylight hours and occasionally running along the ground.
Damage
Damage is similar to that caused by cutworms: seedlings are chewed off at the base and foliage may be chewed as well. Damage usually begins at field edges, as beetles tend to come in from weedy areas, alfalfa, or cover crops. Feeding occurs primarily in the evening and at night. Both larvae and adults can cause damage. After the plants reach a height of 5 to 6 inches, darkling beetles are usually not a problem.
Management
Start inspecting plants for darkling beetle damage when the crop emerges. Inspect on and under the soil line for adult darkling beetles to ensure that a different pest, such as cutworm, did not cause the damage. Apply an insecticide if darkling beetles are causing a reduction in stand of the young plants. Since infestations are frequently spotty, damage and insecticide treatments may be confined to field margins or specific portions of the field.
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(fish) 9 | Leaching(human) 10 | Solution runoff(human) 11 | Last updated 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
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|
Baythroid XL | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
0.8–3.2 | 12 | 7 | — | broad 13 | high | high | high | long | intermediate | intermediate | extra high | very low | very low | 06/2018 | ||
|
|
Bifenture EC | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
1.6–6.4 fl oz | 12 | 14 | — | broad 13 | high | high | high | long | intermediate | low | extra high | very low | intermediate | 06/2018 | ||
|
|
Warrior II | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
0.96–1.92 fl oz | 24 | 21 | Do not graze livestock in treated areas... | broad | high | high | high | long | intermediate | low | extra high | low | high | 06/2018 | ||
|
|
Fyfanon ULV-AG | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
1B |
8 fl oz | 12 | 1 | Do not graze livestock in treated areas... | broad | moderate | high | high | moderate | high | intermediate | extra high | very low | very low | 06/2018 | ||
|
|
Mustang Maxx | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
1.28–4.0 fl oz | 12 | 21 | — | broad 13 | high | moderate | moderate | moderate | intermediate | low | extra high | low | high | 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.
- 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 Harmful mostly to predatory mites rather than pest mites. May cause increase in spider mite numbers.
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
