Description of the Pest
Leafminer adults are very small flies, 0.1 inch (2.5 mm) long, black to blue, with parts of the thorax, legs, and abdomen yellow. Usually there is a prominent yellow area at the base of the wings. The minute white eggs are laid just under the leaf epidermis and hatch in 4 to 6 days. Maggot larvae are normally concealed between leaf surfaces in the mines where they feed; they range from yellow to white, are 0.25 to 0.33 inch long, blunt at the rear end, and pointed in front. Pupation occurs in the mines or in the ground. During summer, the life cycle requires about 23 days. There are from three to five generations a year.
Leafminers are an occasional pest in beans. Generally, their damage occurs during the latter part of the production season. The maggots feed between the upper and lower leaf surfaces causing large whitish blotches, or in the case of serpentine leafminers, slender, white, winding trails through the interior of the leaf. In lima beans, leafminers cause brown, necrotic spots on the leaves.
Because of numerous common parasitoids, leafminers are generally not serious pests. However, they can cause sporadic damage. The destruction of natural enemies by frequent applications of insecticides applied to control other pests can result in leafminer outbreaks. Of the numerous parasitoids that attack leafminers in California, the eulophid wasp, Solenotus intermedius, is the most abundant while Diglyphus spp. and Chrysocharis spp. are probably the most important for controlling leafminers. Plant habitat that attracts natural enemies and avoid the use of broad-spectrum pesticides known to harm natural enemies.
Organically Acceptable Methods
Monitoring and Treatment Decisions
To check for leafminers, evaluate the amount of mining in the leaves during weekly observations for other insect pests beginning at crop emergence. Continue to monitor leaves during vegetative growth, flower bud to bloom, and pod fill stages.
Economic thresholds have not been determined on all bean varieties. On pinks and kidneys, spray if 25% of the surface of older leaves is mined and mines are present in the new leaves.
|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.|
|MODE-OF-ACTION GROUP NUMBER1: 5|
|COMMENTS: Do not apply more than 12 oz per acre per season of Success or 3.75 oz per acre per season of Entrust. For blackeyes, apply with oil.|
|(Agri-Mek SC)||1.7–3.5 fl oz||12||7|
|MODE-OF-ACTION GROUP NUMBER1: 6|
|COMMENTS: Highly toxic to bees; do not spray directly or allow to drift onto blooming crops or weeds where bees are foraging. For use on cowpeas that are grown only for dry seed. Do not allow livestock to graze cowpea forage and do not harvest cowpea forage or hay for use as livestock feed.|
|(Radiant SC)||5–8 fl oz||4||28|
|MODE-OF-ACTION GROUP NUMBER1: 5|
|(Coragen)||7.5 fl oz||4||1|
|MODE-OF-ACTION GROUP NUMBER1: 28|
|MODE-OF-ACTION GROUP NUMBER1: 17|
|COMMENTS: Not registered for cowpea.|
|**||Mix with sufficient water to obtain full coverage.|
|‡||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.|
|#||Acceptable for use on organically grown produce.|
|1||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; pesticides with a 1B group number should be alternated with pesticides that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).|