A Weed Control Program for Establishing Lesquerella

Broad spectrum weed control is essential for successful lesquerella [Lesquerella fendleri (Gray) Wats., Brassicaceae] production. Weeds must be controlled during establishment and throughout the growing season. Lesquerella seedlings grow slowly following germination and emergence, and cannot compete well with most broadleaf and grass weeds. Weed competition is particularly critical prior to closure of the lesquerella canopy, a point sometimes not reached until several months after planting (Roseberg 1996). Weed seedlings can emerge in early fall and interfere with lesquerella growth and establishment. This interference may reduce winter survival of the crop and reduce seed yield. An herbicide program was developed for lesquerella production in Oregon: (1) preplant incorporated trifluralin, benefin, or ethalfluralin; (2) postemergence control of grass weeds—fluazifop-P or sethoxydim; (3) postemergence broadleaf weed control—clopyralid, oxyfluorfen, or pronamide; and (4) layby treatments of DCPA or pendimethalin following cultivation (Roseberg 1996). Several herbicides are registered under Special Local Needs (24c) in Arizona and Texas for weed control in lesquerella when the lesquerella is in the 8 to 10 true-leaf-stage: trifluralin provides adequate preemergence control of annual grasses and broadleaf weeds, fluazifop controls annual and perennial grass weeds postemergence, and oxyfluorfen is used for postemergence control of annual broadleaf weeds (Foster et al. 2005). This program has worked well in establishing large blocks of lesquerella but the postemergence control of broadleaf weeds is still a major problem. Treatments that can be safely applied earlier in the growing season when lesquerella seedlings are smaller (4 to 6 true-leaf-stage) are necessary. Weed escapes from the preemergence treatment germinate along with lesquerella and must be treated when they are small to obtain effective control. Herbicides that offer a broader spectrum of control, and that are more cost effective than oxyfluorfen are also needed. The objective of this research was to determine the tolerance of lesquerella seedlings to alternative postemergence herbicides versus oxyfluorfen (0.6 kg ai/ha) registered under SLN.