Description of the Pest
Flea beetle adults are small (about 0.12 inch), shiny beetles with enlarged hind legs that allow them to jump like fleas. The pale-striped flea beetle has a broad white stripe down each brown wing. Flea beetles can overwinter on weed hosts surrounding fields and in soil and plant residues of previous susceptible crops such as tomatoes and other fruit and vegetable field crops.
Damage
Adult flea beetles do most of the damage by feeding on the undersides of leaves, leaving small pits or irregularly shaped holes on the leaves. Large numbers of flea beetles can kill or stunt seedlings. Older plants rarely suffer economic damage although their older leaves may be damaged. The small, slender, white flea beetle larvae feed on underground parts of the plant, but this damage is not economically significant. Outbreaks of flea beetles in alfalfa seedling fields have occurred in the Central Valley in the fall, but these beetles are also active during springtime.
Management
Cultural Control
Adult flea beetles overwinter in plant debris. To destroy possible refuge sites of adult flea beetles, maintain field sanitation by keeping field margins free from weeds. In case of infested fields, deeply disc plant residue after harvest. Crop rotation with nonhost plants (e.g., cereal grains such as wheat) and maintaining good plant health (e.g., no water stress) are also important for managing flea beetles in alfalfa production.
Organically Acceptable Methods
Only cultural controls are available for this pest on organically grown alfalfa.
Monitoring and Treatment Decisions
Check newly emerged seedlings weekly for flea beetle damage until plants are well established, especially if there was a flea beetle problem in the previous crop. Sometimes infestations can be spotty, for example on field edges when they migrate into alfalfa stands. Relatively low numbers can cause economic damage when plants are in the cotyledon or first-leaf stages. Treat if you find that the flea beetles are causing stand loss. Alfalfa seedling fields need at least 10 to 20 plants per square foot to ensure a viable stand at the end of the first year of production.
Once plants have several true leaves, they can tolerate several beetles per plant without damage. Older plants are even more tolerant. Insecticide applications should rarely be required, but if it is, one application should suffice. However, insecticides may disrupt biological control of aphids, which are increasingly becoming a problem in alfalfa production. Spot treatment of infested areas may be warranted where stand loss is occurring in certain areas of the field, for example on field edges.
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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|
Baythroid XL | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
Label rates | 12 | 7 | Do not spray directly or allow drift ont... | broad | high | high | high | moderate | intermediate | intermediate | extra high | very low | very low | 01/2017 | ||
|
|
Warrior II | Application Timing Varies (See UC IPM Pest Management Guidelines and Label) | 8 |
3A |
Label rates | 24 |
1 (forage) 7 (hay) |
Do not spray directly or allow drift ont... | broad | high | high | high | moderate | intermediate | low | extra high | low | high | 01/2017 |
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.
UC IPM Pest Management Guidelines: Alfalfa
UC ANR Publication 3430
L.D. Godfrey, Entomology, UC Davis
E.T. Natwick (emeritus), UC Cooperative Extension Imperial County
P.B. Goodell (emeritus), UC IPM and Kearney Agricultural Research and Extension Center, Parlier
R.F. Long (emeritus), UC Cooperative Extension Yolo County
V.M. Barlow, UC Cooperative Extension Riverside County
I.M. Grettenberger, Entomology, UC Davis
M.M. Leinfelder-Miles, UC Cooperative Extension San Joaquin, Contra Costa, Sacramento, Solano, and Yolo counties
M.D. Rethwisch, UCCE Riverside Co. (Blythe)
Acknowledgement for Contributions to Invertebrates
D.R. Haviland, UC IPM and UC Cooperative Extension Kern County
C.G. Summers (emeritus), Entomology, UC Davis and Kearney Agricultural Research and Extension Center, Parlier
