How to Manage Pests

UC Pest Management Guidelines

ANNUAL SOWTHISTLE AND PRICKLY LETTUCE. These annual weeds in the Asteraceae (sunflower) family are closely related to lettuce and are often pests in lettuce fields because they are not controlled by lettuce herbicides. Avoid growing lettuce in fields known to be heavily infested with these weeds. Cultural controls, such as crop rotation, preirrigation and cultivation, and cultivation during the growing season, are the best ways to manage these weeds.

SHEPHERD'S-PURSE. Shepherd's-purse is an annual weed in the mustard family that is not controlled by most of the lettuce herbicides. It is also difficult to control with hand hoeing and cultivation because of its high seed production and resultant dense populations. Select fields that are not heavily infested with this weed. Cultural controls, such as crop rotation, preirrigation and cultivation, and cultivating during the growing season, and the use of pronamide are the best choices for control of this weed.

BURNING NETTLE. An annual weed that competes with lettuce, burning nettle also makes harvest difficult because it has stinging hairs on the plant surfaces. Select fields that are not heavily infested with this weed. Control is best achieved culturally with the use of crop rotation, preirrigation and cultivation, and cultivation during the growing season, or with pronamide.

NUTSEDGE. Nutsedge is a serious weed in spring- and summer-planted lettuce. Yellow and purple nutsedge are perennial weeds that reproduce from underground tubers that survive for several years in the soil. Each tuber contains several buds that are capable of producing plants. Only one bud at a time germinates to form a new plant; however, if that bud or plant is destroyed by cultivation or an herbicide, then a new bud is activated. Control is best achieved by continuous cultivation during a summer fallow period or by rotating to crops where effective herbicide and cultural control methods can be used.

COMMON PURSLANE. Three-week or older purslane plants that are cut by cultivation knives still have sufficient resources to set seed. Cut up or uprooted plants can reroot and continue to grow. As a result, purslane populations have increased in some areas. Rogueing and carrying the purslane plants to the edge of the field for subsequent disposal will also reduce future problems with this weed. If increasing problems develop with the weed, treat the entire bed top with any of the labeled preemergent materials, which will control this weed and reduce weed seed production.

PUBLICATION

UC IPM Pest Management Guidelines: Lettuce
UC ANR Publication 3450
Weeds
R. F. Smith, UC Cooperative Extension, Monterey County
S. A. Fennimore, Weed Science/Plant Sciences, UC Davis/Salinas
M. LeStrange, UC Cooperative Extension, Tulare County
Acknowledgment for contributions to Weeds:
D. W. Cudney, Botany, UC Riverside
W. E. Bendixen, UC Cooperative Extension, Santa Barbara County
C. E. Bell, UC Cooperative Extension, San Diego County
W. T. Lanini, Weed Science/Plant Sciences, UC Davis

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