How to Manage Pests

UC Pest Management Guidelines

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.

DAMAGE

Plants heavily attacked by this aphid may wilt during the day. The developing heads remain soft, fail to develop properly, and yields are reduced. Extremely heavy aphid populations 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 are present on roots.

MANAGEMENT

Cultural Control
Remove Lombardy poplars, the overwintering host of the root aphid, in the vicinity of lettuce fields to reduce the severity of root aphid infestations on lettuce. Some varieties of lettuce are resistant to this aphid. Plant these varieties in fields with frequent root aphid problems.

If infested lettuce grows rapidly, a satisfactory crop may often result. Avoid stressing plants and maintain optimum water levels. To help reduce an infestation, eliminate cracks where aphids enter the soil and attack plant roots.

If an infestation occurred on the previous crop, work the soil deeply and allow it to dry thoroughly before replanting to lettuce. Tilling or discing an infested crop will not eliminate the population before replanting.

Organically Acceptable Methods
Cultural controls are organically acceptable.

Chemical Control
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.

Common name		Amount/Acre**	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
When choosing a pesticide, consider information relating to the impact on natural enemies and honey bees and environmental impact. Not all registered pesticides are listed. Always read label of product being used.
A.	IMIDACLOPRID
	(Admire Pro)	7–10.5 oz	12	21
	MODE OF ACTION GROUP NUMBER1: 4A
	COMMENTS: Placement is critical to successful control; see label for details. Do not apply more than 0.38 lb a.i. Admire Pro/acre/year.
B.	DISULFOTON*
	(Di–Syston 8)	1.2 fl oz/1000 ft/row	see label	60
	MODE OF ACTION GROUP NUMBER1: 1B
	COMMENTS: When used at maximum rates under adverse conditions, disulfoton may cause some delay in emergence, stunting of seedlings, or reduction of stand. Such damage may be more pronounced in light sandy soils.
**	Mix with enough water to provide complete coverage.
+	Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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). For additional information, see their Web site at http://www.irac-online.org/.

PUBLICATION

UC IPM Pest Management Guidelines: Lettuce
UC ANR Publication 3450
Insects and Other Arthropods
E. T. Natwick, UC Cooperative Extension, Imperial County
Acknowledgment for contributions to Insects and Mites:
W. E. Chaney, UC Cooperative Extension, Monterey County
N. C. Toscano, Entomology, UC Riverside

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