Description of the Pest
Lettuce root aphids can be distinguished from other aphids found on lettuce by their short antennae (less than one-third body length) and undeveloped cornicles. They are found on lettuce roots in clustered colonies covered with a white powdery wax. Where lettuce or related weeds are not available, these aphids overwinter in the egg stage on the bark of Lombardy poplar. They develop to adults and reproduce once on poplar before migrating to lettuce. On lettuce they begin to feed and reproduce; winged adults develop that can spread from field to field. Lettuce root aphid is a serious pest mostly where lettuce is planted near Lombardy poplars.
Plants heavily attacked by this aphid may wilt during the day. The developing heads remain soft, fails to develop properly, and yields are reduced. Extremely high aphid numbers over a prolonged period can cause collapse and death of the plant. Individual rootlets turn brown and die. Masses of white, woolly material and aphids can be present on the roots.
To prevent lettuce root aphid infestation:
- Avoid planting lettuce in the vicinity of Lombardy poplars, the overwintering host of the root aphid, or remove Lombardy poplars nearby lettuce fields to reduce the severity of root aphid infestations.
- Plant lettuce varieties that have shown resistance in fields with frequent root aphid problems.
- Work the soil deeply and allow it to dry thoroughly if root aphid infestation occurred on the previous crop. Tilling or discing of an infested crop will not eliminate the root aphids before replanting.
- Prevent plant stress and maintain optimum water levels. If infested lettuce grows rapidly, a satisfactory crop may often result.
Organically Acceptable Methods
Use cultural controls in an organically certified crop. Application of entomopathogenic fungus (Mycotrol ESO) together with azadirachtin provided good control of root aphids in similar crops.
An application of imidacloprid banded under the seedline at planting time may prevent infestation by the lettuce root aphid. No insecticides are available to control the root aphid after the lettuce crop is already infested.
Monitoring and Treatment Decisions
- Check for galls on the petioles of Lombardy poplars if they grow in the vicinity. Winged aphids migrate to lettuce fields.
- Look for stunted or wilting lettuce plants in the field and examine their roots for aphid infestations.
|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.|
|(Admire Pro)||7–10.5 oz||12||21|
|MODE-OF-ACTION GROUP NUMBER1: 4A|
|COMMENTS: Soil application. Placement is critical to successful control; see label for details. Do not apply more than 0.38 lb a.i. Admire Pro/acre per year.|
|MODE-OF-ACTION GROUP NUMBER1: 4A|
|MODE-OF-ACTION GROUP NUMBER1: 18B|
|COMMENTS: Restricted use product in an organically certified crop.|
|(Mycotrol ESO)||0.25–1 qt/100 gallons||4||0|
|MODE-OF-ACTION GROUP NUMBER1: –|
|**||Mix with enough water to provide complete 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 organically grown produce.|
|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).|