Agriculture: Alfalfa Pest Management Guidelines

Pale-Striped Flea Beetle

  • Systena blanda
  • 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.


    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.


    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.

    Common name Amount per acre** REI‡ PHI‡
    (Example trade name) (hours) (days)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.
      (Baythroid) Label rates 12 7
      COMMENTS: Do not spray directly or allow drift onto blooming crops or weeds where bees are foraging.
      (Warrior II with Zeon) Label rates 24 1 (forage)
    7 (hay)
      COMMENTS: Do not spray directly or allow drift onto blooming crops or weeds where bees are foraging.
    ** See label for dilution rates.
    Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
    * Permit required from county agricultural commissioner for purchase or use.
    1 Rotate chemicals 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; chemicals with a 1B group number should be alternated with chemicals that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).
    Text Updated: 01/17
    Treatment Table Updated: 01/17