Prickly lettuce

Prickly lettuce

Fall Weed Control: Prickly lettuce — all-season annual or biennial

The issue: Prickly lettuce (Lactuca serriola) is a non-native aster family weed that can germinate throughout the growing season, but mostly in the fall and spring. Plants that enter winter at the rosette stage will survive and send up flower stalks the next spring and summer. Many yellow flowers appear at the end of a flowering stalk that can be anywhere from 4 inches to 6.5 inches tall. There are prickly spines along the bottom of the leaf mid-rib and lower portion of the flowering stalk. The stems, roots and deeply lobed leaves have a milky-white sap. The seeds can be carried long distances on the wind and in irrigation water. Prickly lettuce is very drought tolerant and can be found anywhere. It only reproduces by seed, so all control efforts should be focused on keeping it from going to seed.

Integrated pest management options:

· Mechanical: Tilling, digging, hoeing, hand pulling and field cultivation of prickly lettuce works very well year-round. Plants with seed heads should be thrown away rather than leave them lying on the ground. Mowing is not very effective.

· Cultural: Encourage competition from desirable plants.

· Biological: Livestock and wildlife will graze, but not kill, the plants.

· Chemical: Broadleaf weed control products that contain 2,4-D, MCPP, dicamba, triclopyr, chlorsulfuron, metsulfuron, or glyphosate work very well when applied to the seedling or rosette stage. They are not as effective if the plant has entered the flowering stage. Some herbicides may damage landscape plants even if they are some distance away from the spray site. Be sure the target weed and crop or landscape situations are listed on the product label. Always read and follow herbicide label directions.

Combine them:

Weed control should be in our minds throughout the year. Combine different IPM options to help improve the effectiveness of your efforts.

For more information, contact Ron Patterson, University of Idaho Extension horticulture/agriculture educator in Bonneville County.